In case you missed it, there was a Forbes article on Mi Browser Pro and Mint Browser which are preinstalled on Xiaomi phones. The article accuses Xiaomi of exfiltrating a history of all visited websites. Xiaomi on the other hand accuses Forbes of misrepresenting the facts. They claim that the data collection is following best practices, the data itself being aggregated and anonymized, without any connection to user’s identity.
TL;DR: It is really that bad, and even worse actually.
Update (2021-03-06): It has been close to a year since I wrote this article. In this time Xiaomi did little to address this issue. On the other hand, a similar issue has been discovered in Xiaomi’s payment app, which would even transmit account data to the “analytics” servers. So it can be assumed that other Xiaomi apps are similarly compromised.
Given that neither the Forbes article nor the security researchers involved seem to provide any technical details, I wanted to take a look for myself. I decompiled Mint Browser 3.4.0 and looked for clues. This isn’t the latest version, just in case Xiaomi already modified to code in reaction to the Forbes article. Update (2020-05-08): If you don’t need the technical explanation, the newer article gives an overview of the issue.
Disclaimer: I think that this is the first time I analyzed a larger Android application, so please be patient with me. I might have misinterpreted one thing or another, even though the big picture seems to be clear. Also, my conclusions are based exclusively on code analysis, I’ve never seen this browser in action.
If you are reading this, you probably know already that you are supposed to use two-factor authentication for your most important accounts. This way you make sure that nobody can take over your account merely by guessing or stealing your password, which makes an account takeover far less likely. And what could be more important than your email account that everything else ties into? So you probably know, when Yahoo! greets you like this on login – it’s only for your own safety:
Yahoo! makes sure that “Remind me later” link is small and doesn’t look like an action, so it would seem that adding a phone number is the only way out here. And why would anybody oppose adding it anyway? But here is the thing: complying reduces the security of your account considerably. This is due to the way Verizon Media (the company which acquired Yahoo! and AOL a while ago) implements account recovery. And: yes, everything I say about Yahoo! also applies to AOL accounts.
For some time I thought that jQuery was a thing of the past, only being used in old projects for legacy reasons. I mean, there are now so much better frameworks, why would anyone stick with jQuery and its numerous shortcomings? Then some colleagues told me that they weren’t aware of jQuery’s security downsides. And I recently discovered two big vulnerabilities in antivirus software 12 which existed partly due to excessive use of jQuery. So here is your official public service announcement: jQuery is bad for the security of your project.
By that I don’t mean that jQuery is inherently insecure. You can build a secure project on top of jQuery, if you are sufficiently aware of the potential issues and take care. However, the framework doesn’t make it easy. It’s not secure by default, it rather invites programming practices which are insecure. You have to constantly keep that in mind and correct for it. And if you don’t pay attention just once you will end up with a security vulnerability.
Now an XSS vulnerability in a browser extension is usually very hard to exploit thanks to security mechanisms like Content Security Policy and sandboxing. These mechanisms were intact for McAfee WebAdvisor and I didn’t manage to circumvent them. Yet I still ended up with a proof of concept that demonstrated how attackers could gain local administrator privileges through this vulnerability, something that came as a huge surprise to me as well.
In reality, the data sold by Jumpshot contained plenty of user identifiers, names, email addresses, even home addresses. That’s partly due to Avast being incapable or unwilling to remove user-specific data as they planned to. Many issues are generic however and almost impossible to avoid. This once again underlines the central takeaway: anonymizing browser history data is very hard. That’s especially the case if you plan to sell it to advertisers. You can make data completely anonymous, but you will have to dumb it down so much in the process that advertisers won’t have any use for it any more.
Why did I decide to document Avast’s failure in so much detail? My goal is to spread appreciation for the task of data anonymization: it’s very hard to ensure that no conclusions about users’ identity are possible. So maybe whoever is toying with the idea of collecting anonymized data will better think twice whether they really want do go there. And maybe next time we see a vendor collecting data we’ll ask the right questions about how they ensure it’s a “completely anonymous” process.
But let’s not kid ourselves. Advertisers aren’t interested in data which can’t help them target you. If they really didn’t feel it could help them identify potential customers then the data wouldn’t have any value, and they wouldn’t be interested in paying AVG to access it.
From what I’ve seen now, his statement was spot on and Avast’s data anonymization is nothing but a fig leaf.
Avast took an interesting approach when integrating their antivirus product with web browsers. Users are often hard to convince that Avast browser extensions are good for them and should be activated in their browser of choice. So Avast decided to bring out their own browser with the humble name Avast Secure Browser. Their products send a clear message: ditch your current browser and use Avast Secure Browser (or AVG Secure Browser as AVG users know it) which is better in all respects.
Avast Secure Browser is based on Chromium and its most noticeable difference are the numerous built-in browser extensions, usually not even visible in the list of installed extensions (meaning that they cannot be disabled by regular means). Avast Secure Browser has eleven custom extensions, AVG Secure Browser has eight. Now putting eleven extensions of questionable quality into your “secure” browser might not be the best idea. Today we’ll look at the remarkable Video Downloader extension which essentially allowed any website to take over the browser completely (CVE-2019-18893). An additional vulnerability then allowed it to take over your system as well (CVE-2019-18894). The first issue was resolved in Video Downloader 1.5, released at some point in October 2019. The second issue remains unresolved at the time of writing. Update (2020-01-13): Avast notified me that the second issue has been resolved in an update yesterday, I can confirm the application version not being vulnerable any more after an update.
Note: I did not finish my investigation of the other extensions which are part of the Avast Secure Browser. Given how deeply this product is compromised on another level, I did not feel that there was a point in making it more secure. In fact, I’m not going to write about the Avast Passwords issues I reported to Avast – nothing special here, yet another password manager that made several of the usual mistakes and put your data at risk.
Avast’s official communication throughout that month was nothing short of amazing. I found it hard to believe that a company could keep denying any wrongdoing despite all the evidence to the contrary. Avast’s CEO Ondrej Vlcek even gave an interview to the Forbes magazine where he claimed that there was no privacy scandal here. Users clearly disagreed, and so did most journalists. But the company’s stance didn’t change: all the data collected is necessary to protect users, and selling it later without user’s agreement is completely unproblematic due to the data being “anonymized.”
Let’s say this much up front: the changes are far more extensive and far more convincing than I would have expected. While Chrome and Opera versions appear identical however, there are some additional changes in the Firefox version. That’s presumably to comply with stricter privacy requirements of the Mozilla Add-ons site.
Update (2020-01-10): Avast contacted me to clarify the situation. One piece of information stood out here: “we completely discontinued the practice of using any data from the browser extensions for any other purpose than the core security engine.” In other words, Avast isn’t merely doing the bare minimum required to comply with store policies, they completely give up collecting too much data via their browser extensions and they won’t share this data with anybody either. That’s a massive privacy improvement for any Avast users out there. The open question is whether this policy change also applies to the Avast SafePrice extension and Avast Secure Browser. I’ll update the post again once I have the answer. Update (2020-01-16): The quoted statement from Avast seemed unambiguous, yet further communication established that sharing data with Jumpshot is going to be opt-in functionality for users of the free antivirus application. It’s still an improvement of course but quite different from the initial statement. As to Avast SafePrice and Avast Secure Browser, improvements are expected here in future. Supposedly, the data collected by these was never used, a statement that is impossible to validate.
Just to be clear: with the large codebases and without any official information from Avast I might have overlooked some of the changes. On Firefox I looked at Avast Online Security 19.4.426, on Chrome at Avast Online Security 19.4.433 and on Opera at AVG Online Security 19.4.433.
A while back we’ve seen how Avast monetizes their users. Today we have a much smaller fish to fry, largely because the Avira’s extensions in question aren’t installed by default and require explicit user action for the additional “protection.” So these have far fewer users, currently 400 thousands on Firefox and slightly above a million on Chrome according to official add-on store numbers. It doesn’t make their functionality any less problematic however.
That’s especially the case for Avira Browser Safety extension that Avira offers for Firefox and Opera. While the vendor’s homepage lists “Find the best deals on items you’re shopping for” as last feature in the list, the extension description in the add-on stores “forgets” to mention this monetization strategy. I’m not sure why the identical Chrome extension is called “Avira Safe Shopping” but at least here the users get some transparency.
A month ago I wrote about Avast browser extensions being essentially spyware. While this article only names Avast Online Security and AVG Online Security extensions, the browser extensions Avast SafePrice and AVG SafePrice show the same behavior: they upload detailed browsing profiles of their users to uib.ff.avast.com. The amount of data collected here exceeds by far what would be considered necessary or appropriate even for the security extensions, for the shopping helpers this functionality isn’t justifiable at all.
After I published my article I got the hint to look at Jumpshot, a company acquired by Avast in 2013. And indeed, that suddenly made perfect sense. On their website, Jumpshot praises its “clickstream data” product: