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Introducing the URL validation bypass cheat sheet

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Gotta cache 'em all: bending the rules of web cache exploitation

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Splitting the email atom: exploiting parsers to bypass access controls

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Listen to the whispers: web timing attacks that actually work

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Dark Reading

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Almost Secure

The Karma connection in Chrome Web Store

Somebody brought to my attention that the Hide YouTube Shorts extension for Chrome changed hands and turned malicious. I looked into it and could confirm that it contained two undisclosed components: one performing affiliate fraud and the other sending users’ every move to some Amazon cloud server. But that wasn’t all of it: I discovered eleven more extensions written by the same people. Some contained only the affiliate fraud component, some only the user tracking, some both. A few don’t appear to be malicious yet.

While most of these extensions were supposedly developed or bought by a person without any other traces online, one broke this pattern. Karma shopping assistant has been on Chrome Web Store since 2020, the company behind it founded in 2013. This company employs more than 50 people and secured tons of cash in venture capital. Maybe a mistake on my part?

After looking thoroughly this explanation seems unlikely. Not only does Karma share some backend infrastructure and considerable amounts of code with the malicious extensions. Not only does Karma Shopping Ltd. admit to selling users’ browsing profiles in their privacy policy. There is even more tying them together, including a mobile app developed by Karma Shopping Ltd. whereas the identical Chrome extension is supposedly developed by the mysterious evildoer.

The affected extensions

Most of the extensions in question changed hands relatively recently, the first ones in the summer of 2023. The malicious code has been added immediately after the ownership transfer, with some extensions even requesting additional privileges citing bogus reasons. A few extensions have been developed this year by whoever is behind this.

Some extensions from the latter group don’t have any obvious malicious functionality at this point. If there is tracking, it only covers the usage of the extension’s user interface rather than the entire browsing behavior. This can change at any time of course.

Update (2024-11-11): Hide YouTube Shorts, DarkPDF, Nucleus and Hidden Airline Baggage Fees have been taken down. Two of them have been marked as malware and one as violating Chrome Web Store policies, meaning that existing extension users will be notified. I cannot see the reason for different categorization, the functionality being identical in all of these extensions. The other extensions currently remain active.

Hiding in plain sight

Whoever wrote the malicious code chose not to obfuscate it but to make it blend in with the legitimate functionality of the extension. Clearly, the expectation was that nobody would look at the code too closely. So there is for example this:

if (window.location.href.startsWith("http") ||
    window.location.href.includes("m.youtube.com")) {
  …
}

It looks like the code inside the block would only run on YouTube. Only when you stop and consider the logic properly you realize that it runs on every website. In fact, that’s the block wrapping the calls to malicious functions.

The malicious functionality is split between content script and background worker for the same reason, even though it could have been kept in one place. This way each part looks innocuous enough: there is some data collection in the content script, and then it sends a check_shorts message to the background worker. And the background worker “checks shorts” by querying some web server. Together this just happens to send your entire browsing history into the Amazon cloud.

Similarly, there are some complicated checks in the content script which eventually result in a loadPdfTab message to the background worker. The background worker dutifully opens a new tab for that address and, strangely, closes it after 9 seconds. Only when you sort through the layers it becomes obvious that this is actually about adding an affiliate cookie.

And of course there is a bunch of usual complicated conditions, making sure that this functionality is not triggered too soon after installation and generally doesn’t pop up reliably enough that users could trace it back to this extension.

Affiliate fraud functionality

The affiliate fraud functionality is tied to the kra18.com domain. When this functionality is active, the extension will regularly download data from https://www.kra18.com/v1/selectors_list?&ex=90 (90 being the extension ID here, the server accepts eight different extension IDs). That’s a long list containing 6,553 host names:

Update (2024-11-19): As of now, the owners of this server disabled the endpoints mentioned here. You can still see the original responses on archive.today however.

Whenever one of these domains is visited and the moons are aligned in the right order, another request to the server is made with the full address of the page you are on. For example, the extension could request https://www.kra18.com/v1/extension_selectors?u=https://www.tink.de/&ex=90:

The shortsNavButtonSelector key is another red herring, the code only appears to be using it. The important key is url, the address to be opened in order to set the affiliate cookie. And that’s the address sent via loadPdfTab message mentioned before if the extension decides that right now is a good time to collect an affiliate commission.

There are also additional “selectors,” downloaded from https://www.kra18.com/v1/selectors_list_lr?&ex=90. Currently this functionality is only used on the amazon.com domain and will replace some product links with links going through jdoqocy.com domain, again making sure an affiliate commission is collected. That domain is owned by Common Junction LLC, an affiliate marketing company that published a case study on how their partnership with Karma Shopping Ltd. (named Shoptagr Ltd. back then) helped drive profits.

Browsing profile collection

Some of the extensions will send each page visit to https://7ng6v3lu3c.execute-api.us-east-1.amazonaws.com/EventTrackingStage/prod/rest. According to the extension code, this is an Alooma backend. Alooma is a data integration platform which has been acquired by Google a while ago. Data transmitted could look like this:

Yes, this is sent for each and every page loaded in the browser, at least after you’ve been using the extension for a while. And distinct_id is my immutable user ID here.

But wait, it’s a bit different for the Karma extension. Here you can opt out! Well, that’s only if you are using Firefox because Mozilla is rather strict about unexpected data collection. And if you manage to understand what “User interactions” means on this options page:

Well, I may disagree with the claim that url addresses do not contain personably identifiable information. And: yes, this is the entire page. There really isn’t any more text.

The data transmitted is also somewhat different:

The user_id field no longer contains the extension ID but my personal identifier, complementing the identifier in distinct_id. There is a tab_id field adding more context, so that it is not only possible to recognize which page I navigated to and from where but also to distinguish different tabs. And some more information about my system is always useful of course.

Who is behind this?

Eleven extensions on my list are supposedly developed by a person going by the name Rotem Shilop or Roni Shilop or Karen Shilop. This isn’t a very common last name, and if this person really exists it managed to leave no traces online. Yes, I also searched in Hebrew. Yet one extension is developed by Karma Shopping Ltd. (formerly Shoptagr Ltd.), a company based in Israel with at least 50 employees. An accidental association?

It doesn’t look like it. I’m not going into the details of shared code and tooling, let’s just say: it’s very obvious that all twelve extensions are being developed by the same people. Of course, there is still the possibility that the eleven malicious extensions are not associated directly with Karma Shopping but with some rogue employee or contractor or business partner.

However, it isn’t only the code. As explained above, five extensions including Karma share the same tracking backend which is found nowhere else. They are even sending the same access token. Maybe this backend isn’t actually run by Karma Shopping and they are only one of the customers of some third party? Yet if you look at the data being sent, clearly the Karma extension is considered first-party. It’s the other extensions which are sending external: true and component: external_extension flags.

Then maybe Karma Shopping is merely buying data from a third party, without actually being affiliated with their extensions? Again, this is possible but unlikely. One indicator is the user_id field in the data sent by these extensions. It’s the same extension ID that they use for internal communication with the kra18.com server. If Karma Shopping were granting a third party access to their server, wouldn’t they assign that third party some IDs of their own?

And those affiliate links produced by the kra18.com server? Some of them clearly mention karmanow.com as the affiliate partner.

Finally, if we look at Karma Shopping’s mobile apps, they develop two of them. In addition to the Karma app, the app stores also contain an app called “Sudoku on the Rocks,” developed by Karma Shopping Ltd. Which is a very strange coincidence because an identical “Sudoku on the Rocks” extension also exists in the Chrome Web Store. Here however the developer is Karen Shilop. And Karen Shilop chose to include hidden affiliate fraud functionality in their extension.

By the way, guess who likes the Karma extension a lot and left a five-star review?

I contacted Karma Shopping Ltd. via their public relations address about their relationship to these extensions and the Shilop person but didn’t hear back so far.

Update (2024-10-30): An extension developer told me that they were contacted on multiple independent occasions about selling their Chrome extension to Karma Shopping, each time by C-level executives of the company, from official karmanow.com email addresses. The first outreach was in September 2023, where Karma was supposedly looking into adding extensions to their portfolio as part of their growth strategy. They offered to pay between $0.2 and $1 per weekly active user.

Update (2024-11-11): Another hint pointed me towards this GitHub issue. While the content has been removed here, you can still see the original content in the edit history. It’s the author of the Hide YouTube Shorts extension asking the author of the DarkPDF extension about that Karma company interested in buying their extensions.

What does Karma Shopping want with the data?

It is obvious why Karma Shopping Ltd. would want to add their affiliate functionality to more extensions. After all, affiliate commissions are their line of business. But why collect browsing histories? Only to publish semi-insightful articles on people’s shopping behavior?

Well, let’s have a look at their privacy policy which is actually meaningful for a change. Under 1.3.4 it says:

Browsing Data. In case you a user of our browser extensions we may collect data regarding web browsing data, which includes web pages visited, clicked stream data and information about the content you viewed.

How we Use this Data. We use this Personal Data (1) in order to provide you with the Services and feature of the extension and (2) we will share this data in an aggregated, anonymized manner, for marketing research and commercial use with our business partners.

Legal Basis. (1) We process this Personal Data for the purpose of providing the Services to you, which is considered performance of a contract with you. (2) When we process and share the aggregated and anonymized data we will ask for your consent.

First of all, this tells us that Karma collecting browsing data is official. They also openly state that they are selling it. Good to know and probably good for their business as well.

As to the legal basis: I am no lawyer but I have a strong impression that they don’t deliver on the “we will ask for your consent” promise. No, not even that Firefox options page qualifies as informed consent. And this makes this whole data collection rather doubtful in the light of GDPR.

There is also a difference between anonymized and pseudonymized data. The data collection seen here is pseudonymized: while it doesn’t include my name, there is a persistent user identifier which is still linked to me. It is usually fairly easy to deanonymize pseudonymized browsing histories, e.g. because people tend to visit their social media profiles rather often.

Actually anonymized data would not allow associating it with any single person. This is very hard to achieve, and we’ve seen promises of aggregated and anonymized data go very wrong. While it’s theoretically possible that Karma correctly anonymizes and aggregates data on the server side, this is a rather unlikely outcome for a company that, as we’ve seen above, confuses the lack of names and email addresses with anonymity.

But of course these considerations only apply to the Karma extension itself. Because related extensions like Hide YouTube Shorts just straight out lie:

Some of these extensions actually used to have a privacy policy before they were bought. Now only three still have an identical and completely bogus privacy policy. Sudoku on the Rocks happens to be among these three, and the same privacy policy is linked by the Sudoku on the Rocks mobile apps which are officially developed by Karma Shopping Ltd.

Lies, damned lies, and Impact Hero (refoorest, allcolibri)

Transparency note: According to Colibri Hero, they attempted to establish a business relationship with eyeo, a company that I co-founded. I haven’t been in an active role at eyeo since 2018, and I left the company entirely in 2021. Colibri Hero was only founded in 2021. My investigation here was prompted by a blog comment.

Colibri Hero (also known as allcolibri) is a company with a noble mission:

We want to create a world where organizations can make a positive impact on people and communities.

One of the company’s products is the refoorest browser extension, promising to make a positive impact on the climate by planting trees. Best of it: this costs users nothing whatsoever. According to the refoorest website:

Plantation financed by our partners

So the users merely need to have the extension installed, indicating that they want to make a positive impact. And since the concept was so successful, Colibri Hero recently turned it into an SDK called Impact Hero (also known as Impact Bro), so that it could be added to other browser extensions.

What the company carefully avoids mentioning: its 56,000 “partners” aren’t actually aware that they are financing tree planting. The refoorest extension and extensions using the Impact Hero SDK automatically open so-called affiliate links in the browser, making certain that the vendor pays them an affiliate commission for whatever purchases the users make. As the extensions do nothing to lead users to a vendor’s offers, this functionality likely counts as affiliate fraud.

The refoorest extension also makes very clear promises to its users: planting a tree for each extension installation, two trees for an extension review as well as a tree for each vendor visit. Clearly, this is not actually happening according to the numbers published by Colibri Hero themselves.

What does happen is careless handling of users’ data despite the “100% Data privacy guaranteed” promise. In fact, the company didn’t even bother to produce a proper privacy policy. There are various shady practices including a general lack of transparency, with the financials never disclosed. As proof of trees being planted the company links to a “certificate” which is … surprise! … its own website.

Mind you, I’m not saying that the company is just pocketing the money it receives via affiliate commissions. Maybe they are really paying Eden Reforestation (not actually called that any more) to plant trees and the numbers they publish are accurate. As a user, this is quite a leap of faith with a company that shows little commitment to facts and transparency however.

What is Colibri Hero?

Let’s get our facts straight. First of all, what is Colibri Hero about? To quote their mission statement:

Because more and more companies are getting involved in social and environmental causes, we have created a SaaS solution that helps brands and organizations bring impactful change to the environment and communities in need, with easy access to data and results. More than that, our technology connects companies and non-profit organizations together to generate real impact.

Our e-solution brings something new to the demand for corporate social responsibility: brands and organizations can now offer their customers and employees the chance to make a tangible impact, for free. An innovative way to create an engaged community that feels empowered and rewarded.

You don’t get it? Yes, it took me a while to understand as well.

This is about companies’ bonus programs. Like: you make a purchase, you get ten points for the company’s loyalty program. Once you have a few hundred of those points, you can convert them into something tangible: getting some product for free or at a discount.

And Colibri Hero’s offer is: the company can offer people to donate those points, for a good cause. Like planting trees or giving out free meals or removing waste from the oceans. It’s a win-win situation: people can feel good about themselves, the company saves themselves some effort and Colibri Hero receives money that they can forward to social projects (after collecting their commission of course).

I don’t know whether the partners get any proof of money being donated other than the overview on the Colibri Hero website. At least I could not find any independent confirmation of it happening. All photos published by the company are generic and from unrelated events. Except one: there is photographic proof that some notebooks (as in: paper that you write on) have been distributed to girls in Sierra Leone.

Few Colibri Hero partners report the impact of this partnership or even its existence. The numbers are public on Colibri Hero website however if you know where to look for them and who those partners are. And since Colibri Hero left the directory index enabled for their Google Storage bucket, the logos of their partners are public as well.

So while Colibri Hero never published a transparency report themselves, it’s clear that they partnered up with less than 400 companies. Most of these partnerships appear to have never gone beyond a trial, the impact numbers are negligible. And despite Colibri Hero boasting their partnerships with big names like Decathlon and Foot Locker, the corresponding numbers are rather underwhelming for the size of these businesses.

Colibri Hero runs a shop which they don’t seem to link anywhere but which gives a rough impression of what they charge their partners. Combined with the public impact numbers (mind you, these have been going since the company was founded in 2021), this impression condenses into revenue numbers far too low to support a company employing six people in France, not counting board members and ethics advisors.

And what about refoorest?

This is likely where the refoorest extension comes in. While given the company’s mission statement this browser extension with its less than 100,000 users across all platforms (most of them on Microsoft Edge) sounds like a side hustle, it should actually be the company’s main source of income.

The extension’s promise sounds very much like that of the Ecosia search engine: you search the web, we plant trees. Except that with Ecosia you have to use their search engine while refoorest supports any search engine (as well as Linkedin and Twitter/X which they don’t mention explicitly). Suppose you are searching for a new pair of pants on Google. One of the search results is Amazon. With refoorest you see this:

If you click the search result you go to Amazon as usual. Clicking that added link above the search result however will send you to the refoorest.com domain, where you will be redirected to the v2i8b.com domain (an affiliate network) which will in turn redirect you to amazon.com (the main page, not the pants one). And your reward for that effort? One more tree added to your refoorest account! Planting trees is really easy, right?

One thing is odd about this extension’s listing on Chrome Web Store: for an extension with merely 20,000 users, 2.9K ratings is a lot.

One reason is: the extension incentivizes leaving reviews. This is what the extension’s pop-up looks like:

Review us and we will plant two trees! Give us your email address and we will plant another two trees! Invite fifteen friends and we will plant a whole forest for you!

The newcomer: Impact Hero

Given the success of refoorest, it’s unsurprising that the company is looking for ways to expand this line of business. What they recently came up with is the Impact Hero SDK, or Impact Bro as its website calls it (yes, really). It adds an “eco-friendly mode” to existing extensions. To explain it with the words of the Impact Bros (highlighting of original):

With our eco-friendly mode, you can effortlessly plant trees and offset carbon emissions at no cost as you browse the web. This allows us to improve the environmental friendliness of our extension.

Wow, that’s quite something, right? And how is that possible? That’s explained a little further in the text:

Upon visiting one of these merchant partners, you’ll observe a brief opening of a new tab. This tab facilitates the calculation of the required carbon offset.

Oh, calculation of the required carbon offset, makes sense. That’s why it loads the same website that I’m visiting but via an affiliate network. Definitely not to collect an affiliate commission for my purchases.

Just to make it very clear: the thing about calculating carbon offsets is a bold lie. This SDK earns money via affiliate commissions, very much in the same way as the refoorest extension. But rather than limiting itself to search results and users’ explicit clicks on their link, it will do this whenever the user visits some merchant website.

Now this is quite unexpected functionality. Yet Chrome Web Store program policies require the following:

All functionalities of extensions should be clearly disclosed to the user, with no surprises.

Good that the Impact Hero SDK includes a consent screen, right? Here is what it looks like in the Chat GPT extension:

Yes, this doesn’t really help users make an informed decision. And if you think that the “Learn more” link helps, it leads to the page where I copied the “calculation of the required carbon offset” bullshit from.

The whole point of this “consent screen” seems to be tricking you into granting the extension access to all websites. Consequently, this consent screen is missing from extensions that already have access to all websites out of the box (including the two extensions owned by Colibri Hero themselves).

There is one more area that Colibri Hero focuses on to improve its revenue: their list of merchants that the extensions download each hour. This discussion puts the size of the list at 50 MB on September 6. When I downloaded it on September 17 it was already 62 MB big. By September 28 the list has grown to 92 MB. If this size surprises you: there are lots of duplicate entries. amazon.com alone is present 615 times in that list (some metadata differs, but the extensions don’t process that metadata anyway).

Affected extensions

In addition to refoorest I could identify two extensions bought by Colibri Hero from their original author as well as 14 extensions which apparently added Impact Hero SDK expecting their share of the revenue. That’s Chrome Web Store only, the refoorest extension at the very least also exists in various other extension stores, even though it has been removed from Firefox Add-ons just recently.

Here is the list of extensions I found and their current Chrome Web Store stats:

Edit (2024-10-01): Opera already removed refoorest from their add-on store.

But are they actually planting trees?

That’s a very interesting question, glad you asked. See, refoorest considers itself to be in direct competition with the Ecosia search engine. And Ecosia publishes detailed financial reports where they explain how much money they earn and where it went. Ecosia is also listed as a partner on the Eden: People+Planet website, so we have independent confirmation here that they in fact donated at least a million US dollars.

I searched quite thoroughly for comparable information on Colibri Hero. All I could find was this statement:

We allocate a portion of our income to operating expenses, including team salaries, social charges, freelancer payments, and various fees (such as servers, technical services, placement fees, and rent). Additionally, funds are used for communications to maximize the service’s impact. Then, 80% of the profits are donated to global reforestation projects through our partner, Eden Reforestation.

While this sounds good in principle, we have no idea how high their operational expenses are. Maybe they are donating half of their revenue, maybe none. Even if this 80% rule is really followed, it’s easy to make operational expenses (like the salary of the company founders) so high that there is simply no profit left.

Edit (2024-10-01): It seems that I overlooked them in the list of partners. So they did in fact donate at least 50 thousand US dollars. Thanks to Adrien de Malherbe of Colibri Hero for pointing this out. Edit (2024-10-02): According to the Internet Archive, refoorest got listed here in May 2023 and they have been in the “$50,000 - $99,999” category ever since. They were never listed with a smaller donation, and they never moved up either – almost like this was a one-time donation. As of October 2024, the Eden: People+Planet website puts the cost of planting a tree at $0.75.

And other than that they link to the certificate of the number of trees planted:

But that’s their own website, just like the maps of where trees are being planted. They can make it display any number.

Now you are probably thinking: “Wladimir, why are you so paranoid? You have no proof that they are lying, just trust them to do the right thing. It’s for a good cause!” Well, actually…

Remember that the refoorest extension promises its users to plant a specific number of trees? One for each extension installation, two for a review, one more tree each time a merchant website is visited? What do you think, how many trees came together this way?

One thing about Colibri Hero is: they don’t seem to be very fond of protecting data access. Not only their partners’ stats are public, the user data is as well. When the extension loads or updates the user’s data, there is no authentication whatsoever. Anybody can just open my account’s data in their browser provided that they know my user ID:

So anybody can track my progress – how many trees I’ve got, when the extension last updated my data, that kind of thing. Any stalkers around? Older data (prior to May 2022) even has an email field, though this one was empty for the accounts I saw.

How you might get my user ID? Well, when the extension asks me to promote it on social networks and to my friends, these links contain my user ID. There are plenty of such links floating around. But as long as you aren’t interested in a specific user: the user IDs are incremental. They are even called row_index in the extension source code.

See that index value in my data? We now know that 2,834,418 refoorest accounts were created before I decided to take a look. Some of these accounts certainly didn’t live long, yet the average still seems to be beyond 10 trees. But even ignoring that: two million accounts are two million trees just for the install.

According to their own numbers refoorest planted less that 700,000 trees, far less than those accounts “earned.” In other words: when these users were promised real physical trees, that was a lie. They earned virtual points to make them feel good, when the actual count of trees planted was determined by the volume of affiliate commissions.

Wait, was it actually determined by the affiliate commissions? We can get an idea by looking at the historical data for the number of planted trees. While Colibri Hero doesn’t provide that history, the refoorest website was captured by the Internet Archive at a significant number of points in time. I’ve collected the numbers and plotted them against the respective date. Nothing fancy like line smoothing, merely lines connecting the dots:

Well, that’s a straight line. There is a constant increase rate of around 20 trees per hour here. And I hate to break it to you, a graph like that is rather unlikely to depend on anything related to the extension which certainly grew its user base over the course of these four years.

There are only two anomalies here where the numbers changed non-linearly. There is a small jump end of January or start of February 2023. And there is a far larger jump later in 2023 after a three month period where the Internet Archive didn’t capture any website snapshots, probably because the website was inaccessible. When it did capture the number again it was already above 500,000.

The privacy commitment

Refoorest website promises:

100% Data privacy guaranteed

The Impact Hero SDK explainer promises:

This new feature does not retain any information or data, ensuring 100% compliance with GDPR laws.

Ok, let’s first take a look at their respective privacy policies. Here is the refoorest privacy policy:

If you find that a little bit hard to read, that’s because whoever copied that text didn’t bother to format lists and such. Maybe better to read it on the Impact Bro website?

Sorry, that’s even worse. Not even the headings are formatted here.

Either way, nothing shows appreciation for privacy like a standard text which is also used by pizza restaurants and similarly caring companies. Note how that references “Law No. 78-17 of 6 January 1978”? That’s some French data protection law that I’m pretty certain is superseded by GDPR. A reminder: GDPR came in effect in 2018, three years before Colibri Hero was even founded.

This privacy policy isn’t GDPR-compliant either. For example, it has no mention of consumer rights or who to contact if I want my data to be removed.

Data like what’s stored in those refoorest accounts which happen to be publicly visible. Some refoorest users might actually find that fact unexpected.

Or data like the email address that the extension promises two trees for. Wait, they don’t actually have that one. The email address goes straight to Poptin LTD, a company registered in Israel. There is no verification that the user owns the address like double opt-in. But at least Poptin has a proper GDPR-compliant privacy policy.

There is plenty of tracking going on all around refoorest, with data being collected by Cloudflare, Google, Facebook and others. This should normally be explained in the privacy policy. Well, not in this one.

Granted, there is less tracking around the Impact Hero SDK, still a far shot away from the “not retain any information or data” promise however. The “eco-friendly mode” explainer loads Google Tag Manager. The affiliate networks that extensions trigger automatically collect data, likely creating profiles of your browsing. And finally: why is each request going through a Colibri Hero website before redirecting to the affiliate network if no data is being collected there?

Happy users

We’ve already seen that a fair amount of users leaving a review for the refoorest extension have been incentivized to do so. That’s the reason for “insightful” reviews like this one:

Funny enough, several of them then complain about not receiving their promised trees. That’s due to an extension issue: the extension doesn’t actually track whether somebody writes a review, it simply adds two trees with a delay after the “Leave a review” button is clicked. A bug in the code makes it “forget” that it meant to do this if something else happens in between. Rather that fixing the bug they removed the delay in the current extension version. The issue is still present when you give them your email address though.

But what about the user testimonies on their webpage?

Yes, this sounds totally like something real users would say, definitely not written by a marketing person. And these user photos definitely don’t come from something like the Random User Generator. Oh wait, they do.

In that context it makes sense that one of the company’s founders engages with the users in a blog titled “Eco-Friendly Living” where he posts daily articles with weird ChatGPT-generated images. According to metadata, all articles have been created on the same date, and each article took around four minutes – he must be a very fast typer. Every article presents a bunch of brands, and the only thing (currently) missing to make the picture complete are affiliate links.

Security issue

It’s not like the refoorest extension or the SDK do much. Given that, the company managed to produce a rather remarkable security issue. Remember that their links always point to a Colibri Hero website first, only to be redirected to the affiliate network then? Well, for some reason they thought that performing this redirect in the extension was a good idea.

So their extension and their SDK do the following:

if (window.location.search.indexOf("partnerurl=") > -1) {
  const url = decodeURIComponent(gup("partnerurl", location.href));

  location.href = url;

  return;
}

Found a partnerurl parameter in the query string? Redirect to it! You wonder what websites this code is active on? All of them of course! What could possibly go wrong…

Well, the most obvious thing to go wrong is: this might be a javascript: URL. A malicious website could open https://example.com/?partnerurl=javascript:alert(1) and the extension will happily navigate to that URL. This almost became a Universal Cross-Site Scripting (UXSS) vulnerability. Luckily, the browser prevents this JavaScript code from running, at least with Manifest V3.

It’s likely that the same vulnerability already existed in the refoorest extension back when it was using Manifest V2. At that point it was a critical issue. It’s only with the improvements in Manifest V3 that extensions’ content scripts are subject to a Content Security Policy which prevents execution of arbitrary Javascript code.

So now this is merely an open redirect vulnerability. It could be abused for example to disguise link targets and abuse trust relationships. A link like https://example.com/?partnerurl=https://evil.example.net/ looks like it would lead to a trusted example.com website. Yet the extension would redirect it to the malicious evil.example.net website instead.

Conclusions

We’ve seen that Colibri Hero is systematically misleading extension users about the nature of its business. Users are supposed to feel good about doing something for the planet, and the entire communication suggests that the “partners” are contributing finances due to sharing this goal. The aspect of (ab)using the system of affiliate marketing is never disclosed.

This is especially damning in case of the refoorest extension where users are being incentivized by a number of trees supposedly planted as a result of their actions. At no point does Colibri Hero disclose that this number is purely virtual, with the actual count of trees planted being far lower and depending on entirely different factors. Or rather no factors at all if their reported numbers are to be trusted, with the count of planted trees always increasing at a constant rate.

For the Impact Hero SDK this misleading communication is paired with clearly insufficient user consent. Most extensions don’t ask for user consent at all, and those that do aren’t allowing an informed decision. The consent screen is merely a pretense to trick the users into granting extended permissions.

This by itself is already in gross violation of the Chrome Web Store policies and warrants a takedown action. Other add-on stores have similar rules, and Mozilla in fact already removed the refoorest extension prior to my investigation.

Colibri Hero additionally shows a pattern of shady behavior, such as quoting fake user testimonies, referring to themselves as “proof” of their beneficial activity and a general lack of transparency about finances. None of this is proof that this company isn’t donating money as it claims to do, but it certainly doesn’t help trusting them with it.

The technical issues and neglect for users’ privacy are merely a sideshow here. These are somewhat to be expected for a small company with limited financing. Even a small company can do better however if the priorities are aligned.

How insecure is Avast Secure Browser?

A while ago I already looked into Avast Secure Browser. Back then it didn’t end well for Avast: I found critical vulnerabilities allowing arbitrary websites to infect user’s computer. Worse yet: much of it was due to neglect of secure coding practices, existing security mechanisms were disabled for no good reason. I didn’t finish that investigation because I discovered that the browser was essentially spyware, collecting your browsing history and selling it via Avast’s Jumpshot subsidiary.

But that was almost five years ago. After an initial phase of denial, Avast decided to apologize and to wind down Jumpshot. It was certainly a mere coincidence that Avast was subsequently sold to NortonLifeLock, called Gen Digital today. Yes, Avast is truly reformed and paying for their crimes in Europe and the US. According to the European decision, Avast is still arguing despite better knowledge that their data collection was fully anonymized and completely privacy-conformant but… well, old habits are hard to get rid of.

Either way, it’s time to take a look at Avast Secure Browser again. Because… all right, because of the name. That was a truly ingenious idea to name their browser like that, nerd sniping security professionals into giving them free security audits. By now they certainly would have addressed the issues raised in my original article and made everything much more secure, right?

Note: This article does not present any actual security vulnerabilities. Instead, this is a high-level overview of design decisions that put users at risk, artificially inflating the attack surface and putting lots of trust into the many, many companies involved with the Avast webspaces. TL;DR: I wouldn’t run Avast Secure Browser on any real operating system, only inside a virtual machine containing no data whatsoever.

Summary of the findings

The issues raised in my original article about the pre-installed browser extensions are still partially present. Two extensions are relaxing the default protection provided by Content-Security-Policy even though it could have been easily avoided. One extension is requesting massive privileges, even though it doesn’t actually need them. At least they switched from jQuery to React, but they still somehow managed to end up with HTML injection vulnerabilities.

In addition, two extensions will accept messages from any Avast website – or servers pretending to be Avast websites, since HTTPS-encrypted connections aren’t being enforced. In the case of the Privacy Guard (sic!) extension, this messaging exposes users’ entire browsing information to websites willing to listen. Yes, Avast used to collect and sell that information in the past, and this issue could in principle allow them to do it again, this time in a less detectable way.

The Messaging extension is responsible for the rather invasive “onboarding” functionality of the browser, allowing an Avast web server to determine almost arbitrary rules to nag the user – or to redirect visited websites. Worse yet, access to internal browser APIs has been exposed to a number of Avast domains. Even if Avast (and all the other numerous companies involved in running these domains) are to be trusted, there is little reason to believe that such a huge attack surface can possibly be secure. So it has to be expected that other websites will also be able to abuse access to these APIs.

What is Avast Secure Browser?

Avast Secure Browser is something you get automatically if you don’t take care while installing your Avast antivirus product. Or AVG antivirus. Or Avira. Or Norton. Or CCleaner. All these brands belong to Gen Digital now, and all of them will push Avast Secure Browser under different names.

According to their web page, there are good reasons to promote this browser:

So one of the reasons is: this browser is 100% free. And it really is, as in: “you are the product.” I took the liberty of making a screenshot of the browser and marking the advertising space:

Yes, maybe this isn’t entirely fair. I’m still indecisive as to whether the search bar should also be marked. The default search engine is Bing and the browser will nudge you towards keeping it selected. Not because Microsoft’s search engine is so secure and private of course but because they are paying for it.

But these are quality ads and actually useful! Like that ad for a shop selling food supplements, so that you can lead a healthy life. A quick search reveals that one of the three food supplements shown in the ad is likely useless with the suspicion of being harmful. Another brings up lots of articles by interested parties claiming great scientifically proven benefits but no actual scientific research on the topic. Finally the third one could probably help a lot – if there were any way of getting it into your body in sufficient concentration, which seems completely impossible with oral intake.

Now that we got “free” covered, we can focus on the security and privacy aspects in the subsequent sections.

The pre-installed extensions

There are various reasons for browser vendors to pre-package extensions with their browser. Mozilla Firefox uses extensions to distribute experimental features before they become an integral part of the browser. As I learned back in 2011, Google Chrome uses such extensions to promote their web applications and give them an advantage over competition. And as Simon Willison discovered only a few days ago, the Google Hangouts extension built into Google Chrome gives Google domains access to internal browser APIs – quite nifty if one wants better user tracking capabilities.

My previous article mentioned Avast Secure Browser adding eleven extensions to the ones already built into Google Chrome. This number hasn’t changed: I still count eleven extensions, even though their purposes might have changed. At least that’s eleven extensions for me, differently branded versions of this browser seem to have a different combination of extensions. Only two of these extensions (Coupons and Video Downloader) are normally visible in the list of extensions and can be easily disabled. Three more extensions (Avast Bank Mode, Avast SecureLine VPN, Privacy Guard) become visible when Developer Mode is switched on.

And then there are five extensions that aren’t visible at all and cannot be disabled by regular means: Anti-Fingerprinting, Messaging, Side Panel, AI Chat, Phishing Protection. Finally, at least the New Tab extension is hardwired into the browser and is impossible to disable.

Now none of this is a concern if these extensions are designed carefully with security and privacy in mind. Are they?

Security mechanisms disabled

My previous article described the Video Downloader extension as a huge “please hack me” sign. Its extension manifest requested every permission possible, and it also weakened Content-Security-Policy (CSP) protection by allowing execution of dynamic scripts. Both were completely unnecessary, my proof of concept exploit abused it to get a foothold in the Avast Secure Browser.

Looking at the current Video Downloader manifest, things are somewhat better today:

{
  "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",
  "permissions": [
    "activeTab", "downloads", "management", "storage", "tabs", "webRequest",
    "webRequestBlocking", "<all_urls>"
  ],
}

The permissions requested by this extension still grant it almost arbitrary access to all websites. But at least the only unused privilege on this list is management which gives it the ability to disable or uninstall other extensions.

As to CSP, there is still 'unsafe-eval' which allowed this extension to be compromised last time. But now it’s there for a reason: Video Downloader “needs” to run some JavaScript code it receives from YouTube in order to extract some video metadata.

I did not test what this code is or what it does, but this grants at the very least the YouTube website the ability to compromise this extension and, via it, the integrity of the entire browser. But that’s YouTube, it won’t possibly turn evil, right?

For reference: it is not necessary to use 'unsafe-eval' to run some untrusted code. It’s always possible to create an <iframe> element and use the sandbox attribute to execute JavaScript code in it without affecting the rest of the extension.

But there are more extensions. There is the Avast Bank Mode extension for example, and its extension manifest says:

{
  "content_security_policy": "script-src 'self' 'unsafe-eval'; object-src 'self'",
  "permissions": [
    "activeTab", "alarms", "bookmarks", "browsingData", "clipboardRead",
    "clipboardWrite", "contentSettings", "contextMenus", "cookies", "debugger",
    "declarativeContent", "downloads", "fontSettings", "geolocation", "history",
    "identity", "idle", "management", "nativeMessaging", "notifications",
    "pageCapture", "power", "privacy", "proxy", "sessions", "storage", "system.cpu",
    "system.display", "system.memory", "system.storage", "tabCapture", "tabs", "tts",
    "ttsEngine", "unlimitedStorage", "webNavigation", "webRequest",
    "webRequestBlocking", "http://*/*", "https://*/*", "<all_urls>"
  ],
}

Yes, requesting every possible permission and allowing execution of dynamic scripts at the same time, the exact combination that wreaked havoc last time. Why this needs 'unsafe-eval'? Because it uses some ancient webpack version that relies on calling eval() in order to “load” JavaScript modules dynamically. Clearly, relaxing security mechanisms was easier than using a better module bundler (like the one used by other Avast extensions).

The (lack of) ad blocking privacy

The Privacy Guard extension is responsible for blocking ads and trackers. It is meant by the sentence “block ads and boost your online privacy” in the website screenshot above. It is also one of the two extensions containing the following entry in its manifest:

{
  "externally_connectable": {
    "ids": [ "*" ],
    "matches": [
      "*://*.avastbrowser.com/*",
      "*://*.avgbrowser.com/*",
      "*://*.ccleanerbrowser.com/*",
      "*://*.avast.com/*",
      "*://*.securebrowser.com/*"
    ]
  },
}

What this means: any other extension installed is allowed to send messages to the Privacy Guard extension. That isn’t restricted to Avast extensions, any other extension you installed from Avast’s or Google’s add-on store is allowed to do this as well.

The same is true for any website under the domains avast.com, securebrowser.com, avastbrowser.com, avgbrowser.com or ccleanerbrowser.com. Note that the rules here don’t enforce https:// scheme, unencrypted HTTP connections will be allowed as well. And while avast.com domain seems to be protected by HTTP Strict Transport Security, the other domains are not.

Why this matters: when your browser requests example.securebrowser.com website over an unencrypted HTTP connection, it cannot be guaranteed that your browser is actually talking to an Avast web server. In fact, any response is guaranteed to come from a malicious web server because to such website exists.

One way you might get a response from such a malicious web server is connecting to a public WiFi. In principle, anyone connected to the same WiFi could redirect unencrypted web requests to their own malicious web server, inject an invisible request to example.securebrowser.com in a frame (which would also be handled by their malicious server) and gain the ability to message Privacy Guard extension. While not common, this kind of attack did happen in the wild.

And what does someone get then? Let me show you:

chrome.runtime.connect("onochehmbbbmkaffnheflmfpfjgppblm", {name: "PG_STORE"})
  .onMessage.addListener(x => console.log(x));

This establishes a connection to the extension and logs all incoming messages. One message is received immediately:

{
  "type": "chromex.state",
  "payload": {
    "main": {
      "settings": {
        "paused": false,
        "off": false,
        "blockingMode": "strict",
        "showIconBadge": true,
        "fingerprintEnabled": true,
        "previousBlockingModeIsOff": false
      },
      "pausedDomains": [],
      "whitelist": [],
      "afpWhitelist": [],
      "installationInfo": {
        "hostPrefix": "",
        "noProBrand": false,
        "urls": {
          "faqUrl": "https://extension.securebrowser.com/privacy-guard/learn-more/",
          "proUrl": "https://extension.securebrowser.com/privacy-guard/offer/"
        },
        "whitelists": {
          "whitelist": "https://update.avastbrowser.com/adblock/assets/v3/document_whitelist.txt",
          "filterWhitelist": "https://update.avastbrowser.com/adblock/assets/v3/filter_whitelist.txt",
          "searchWhitelist": "https://update.avastbrowser.com/adblock/assets/v3/search_document_whitelist.txt"
        }
      },
      "isProUser": false,
      "blockedAdsCount": 12
    },
    "tabs": {
      "391731034": {
        "adsBlocked": 0,
        "fingerprintAttempts": 0,
        "adsAllowed": 0,
        "listAdsBlocked": [],
        "listAdsAllowed": [],
        "pageAllowed": false,
        "isInternal": false,
        "domainIsPaused": false,
        "isInUserWhitelist": false,
        "isInUserAfpWhitelist": false,
        "netFilteringSwitch": true,
        "active": true,
        "audible": false,
        "autoDiscardable": true,
        "discarded": false,
        "groupId": -1,
        "height": 514,
        "highlighted": true,
        "id": 391731034,
        "incognito": false,
        "index": 2,
        "lastAccessed": 1720641256405.484,
        "mutedInfo": {
          "muted": false
        },
        "openerTabId": 391731032,
        "pendingUrl": "secure://newtab/",
        "pinned": false,
        "selected": true,
        "status": "complete",
        "title": "Example Domain",
        "url": "https://example.com/",
        "width": 299,
        "windowId": 391730998,
        "favIconUrl": "https://example.com/favicon.ico"
      },
      "-1": {
        "adsBlocked": 0,
        "fingerprintAttempts": 0,
        "adsAllowed": 0,
        "listAdsBlocked": [],
         "listAdsAllowed": [],
        "isInternal": true
      },
      "active": 391731034
    }
  }
}

The first part are the Privacy Guard settings, your whitelisted domains, everything. There are also the three hardcoded lists containing blocking exceptions – funny how Avast doesn’t seem to mention these anywhere in the user interface or documentation. I mean, it looks like in the default “Balanced Mode” their ad blocker won’t block any ads on Amazon or eBay among other things. Maybe Avast should be more transparent about that, or people might get the impression that this has something to do with those sponsored bookmarks.

And then there is information about all your browsing tabs which I shortened to only one tab here. It’s pretty much all information produced by the tabs API, enriched with some information on blocked ads. Privacy Guard will not merely send out the current state of your browsing session, it will also send out updates whenever something changes. To any browser extension, to any Avast website and to any web server posing as an Avast website.

Does Avast abuse this access to collect users’ browsing data again? It’s certainly possible. As long as they only do it for a selected subset of users, this would be very hard to detect however. It doesn’t help that Avast Secure Browser tracks virtual machine usage among other things, so it’s perfectly plausible that this kind of behavior won’t be enabled for people running one. It may also only be enabled for people who opened the browser a given number of times after installing it, since this is being tracked as well.

Can other browser extensions abuse this to collect users’ browsing data? Absolutely. An extension can declare minimal privileges, yet it will still be able to collect the entire browsing history thanks to Privacy Guard.

Can a malicious web server abuse this to collect users’ browsing data beyond a single snapshot of currently open tabs? That’s more complicated since this malicious web server would need its web page to stay open permanently somehow. While Avast has the capabilities to do that (more on that below), an arbitrary web server normally doesn’t and has to resort to social engineering.

The messaging interface doesn’t merely allow reading data, the data can also be modified almost arbitrarily as well. For example, it’s possible to enable ad blocking without any user interaction. Not that it changes much, the data collection is running whether ad blocking is enabled or not.

This messaging interface can also be used to add exceptions for arbitrary domains. And while Privacy Guard options page is built using React.js which is normally safe against HTML injections, in one component they chose to use a feature with the apt name dangerouslySetInnerHTML. And that component is used among other things for displaying, you guessed it: domain exceptions.

This is not a Cross-Site Scripting vulnerability, thanks to CSP protection not being relaxed here. But it allows injecting HTML content, for example CSS code to mess with Privacy Guard’s options page. This way an attacker could ensure that exceptions added cannot be removed any more. Or they could just make Privacy Guard options unusable altogether.

The onboarding experience

The other extension that can be messaged by any extension or Avast web server is called Messaging. Interestingly, Avast went as far as disabling Developer Tools for it, making it much harder to inspect its functionality. I don’t know why they did it, maybe they were afraid people would freak out when they saw the output it produces while they are browsing?

You wonder what is going on? This extension processes some rules that it downloaded from https://config.avast.securebrowser.com/engagement?content_type=messaging,messaging_prefs&browser_version=126.0.25496.127 (with some more tracking parameters added). Yes, there is a lot of info here, so let me pick out one entry and explain it:

{
  "post_id": 108341,
  "post_title": "[190] Switch to Bing provider – PROD; google",
  "engagement_trigger_all": [
    {
      "parameters": [
        {
          "operator": "s_regex",
          "value": "^secure:\\/\\/newtab",
          "parameter": {
            "post_id": 11974,
            "name": "url_in_tab",
            "post_title": "url_in_tab",
            "type": "string"
          }
        }
      ]
    },
    {
      "parameters": [
        {
          "operator": "s_regex",
          "value": "google\\.com",
          "parameter": {
            "post_id": 25654,
            "name": "setting_search_default",
            "post_title": "setting_search_default (search provider)",
            "type": "string"
          }
        }
      ]
    }
  ],
  "engagement_trigger_any": [
    {
      "parameters": [
        {
          "operator": "equals",
          "value": "0",
          "parameter": {
            "post_id": 19236,
            "name": "internal.triggerCount",
            "post_title": "internal.triggerCount",
            "type": "number"
          }
        }
      ]
    },
    {
      "parameters": [
        {
          "operator": "n_gte",
          "value": "2592000",
          "parameter": {
            "post_id": 31317,
            "name": "functions.interval.internal.triggered_timestamp",
            "post_title": "interval.internal.triggered_timestamp",
            "type": "number"
          }
        }
      ]
    }
  ],
  "engagement_trigger_none": [],
  …
}

The engagement_trigger_all entry lists conditions that have all be true: you have to be on the New Tab page, and your search provider has to be Google. The engagement_trigger_any entry lists conditions where any one is sufficient: this particular rule should not have been triggered before, or it should have been triggered more than 2592000 seconds (30 days) ago. Finally, engagement_trigger_none lists conditions that should prevent this rule from applying. And if these conditions are met, the Messaging extension will inject a frame into the current tab to nag you about switching from Google to Bing:

Another rule will nag you every 30 days about enabling the Coupons extension, also a cash cow for Avast. There will be a nag to buy the PRO version for users opening a Private Browsing window. And there is more, depending on the parameters sent when downloading these rules probably much more.

An interesting aspect here is that these rules don’t need to limit themselves to information provided to them. They can also call any function of private Avast APIs under the chrome.avast, chrome.avast.licensing and chrome.avast.onboarding namespaces. Some API functions which seem to be called in this way are pretty basic like isPrivateWindow() or isConnectedToUnsafeWifi(), while gatherInfo() for example will produce a whole lot of information on bookmarks, other browsers and Windows shortcuts.

Also, displaying the message in a frame is only one possible “placement” here. The Messaging extension currently provides eight different user interface choices, including straight out redirecting the current page to an address provided in the rule. But don’t worry: Avast is unlikely to start redirecting your Google searches to Bing, this would raise too many suspicions.

Super-powered websites

Why is the Messaging extension allowing some Avast server to run browser APIs merely a side-note in my article? Thing is: this extension doesn’t really give this server anything that it couldn’t do all by itself. When it comes to Avast Secure Browser, Avast websites have massive privileges out of the box.

The browser grants these privileges to any web page under the avast.com, avg.com, avastbrowser.com, avgbrowser.com, ccleanerbrowser.com and securebrowser.com domains. At least here HTTPS connections are enforced, so that posing as an Avast website won’t be possible. But these websites automatically get access to:

• chrome.bookmarks API: full read/write access to bookmarks
• chrome.management API: complete access to extensions except for the ability to install them
• chrome.webstorePrivate API: a private browser API that allows installing extensions.
• A selection of private Avast APIs:
  • chrome.avast
  • chrome.avast.licensing
  • chrome.avast.ntp
  • chrome.avast.onboarding
  • chrome.avast.ribbon
  • chrome.avast.safebrowsing
  • chrome.avast.safesearch
  • chrome.avast.stats
  • chrome.avast.themes

Now figuring out what all these private Avast APIs do in detail, what their abuse potential is and whether any of their crashes are exploitable requires more time than I had to spend on this project. I can see that chrome.avast.ntp API allows manipulating the tiles displayed on the new tab page in arbitrary ways, including reverting all your changes so that you only see those sponsored links. chrome.avast.onboarding API seems to allow manipulating the “engagement” data mentioned above, so that arbitrary content will be injected into tabs matching any given criteria. Various UI elements can be triggered at will. I’ll leave figuring out what else these can do to the readers. If you do this, please let me know whether chrome.avast.browserCall() can merely be used to communicate with Avast’s Security & Privacy Center or exposes Chromium’s internal messaging.

But wait, this is Avast we are talking about! We all know that Avast is trustworthy. After all, they promised to the Federal Trade Commission that they won’t do anything bad any more. And as I said above, impersonating an Avast server won’t be possible thanks to HTTPS being enforced. Case closed, no issue here?

Not quite, there are far more parties involved here. Looking only at www.avast.com, there is for example OneTrust who are responsible for the cookie banners. Google, Adobe, hotjar, qualtrics and mpulse are doing analytics (a.k.a. user tracking). A Trustpilot widget is also present. There is some number of web hosting providers involved (definitely Amazon, likely others as well) and at least two content delivery networks (Akamai and Cloudflare).

And that’s only one host. Looking further, there is a number of different websites hosted under these domains. Some are used in production, others are experiments, yet more appear to be abandoned in various states of brokenness. Some of these web services seem to be run by Avast while others are clearly run by third parties. There is for some reason a broken web shop run by a German e-commerce company, same that used to power Avira’s web shop before Gen Digital bought them.

If one were to count it all together, I would expect that a high two digit number of companies can put content on the domains mentioned above. I wouldn’t be surprised however if that number even went into three digits. Every single one of these companies can potentially abuse internal APIs of the Avast Secure Browser, either because they decide to make some quick buck, are coerced into cooperation by their government or their networks simply get compromised.

And not just that. It isn’t necessary to permanently compromise one of these web services. A simple and very common Cross-Site Scripting vulnerability in any one of these web services would grant any website on the internet access to these APIs. Did Avast verify the security and integrity of each third-party service they decided to put under these domains? I very much doubt so.

It would appear that the official reason for providing these privileges to so many websites was aiding the onboarding experience mentioned above. Now one might wonder whether such a flexible and extensive onboarding process is really necessary. But regardless of that, the reasonable way of doing this is limiting the attack surface. If you need to grant privileges to web pages, you grant them to a single host name. You make sure that this single host name doesn’t run any more web services than it absolutely needs, and that these web services get a proper security review. And you add as many protection layers as possible, e.g. the Content-Security-Policy mechanism which is severely underused on Avast websites.

I’ll conclude by quoting the decision to penalize Avast for their GDPR violations:

At this point, the Appellate Authority considers it necessary to recall that the Charged Company provides software designed to protect the privacy of its users. As a professional in the information and cyber field, the Charged Company is thereby also expected to be extremely knowledgeable in the field of data protection.

Yeah, well…

Packet Storm

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