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A team of Belgian researchers discovered privacy issues in how browsers, ad-blocking, and anti-tracking implementations handle third-party cookie requests.

 

A team of Belgian researchers from KU Leuven analyzed third-party cookie policies of seven major web browsers, 31 ad-blockers and 14 anti-tracking extensions and discovered major and minor issues in all of them.

 

Major issues include Microsoft Edge's unwillingness to honor its own "block only third-party cookies" setting, bypasses for Firefox's Tracking Protection feature, and use of the integrated PDF viewer in Chrome and other Chromium-based browsers for invisible tracking.

 

Cookie requests can be sorted into two main groups: first-party requests that come from the address listed in the address bar of the browser and third-party requests that come from all other sites.

 

Advertisement displayed by websites makes use of cookies usually and some of these cookies are used for tracking purposes.

 

Internet users can configure their browsers to block any third-party cookie requests to limit cookie-based tracking. Some browsers, for instance Opera or Firefox, include ad-blockers or anti-tracking functionality that is used in addition to that.

Anti-tracking mechanisms have flaws

The research paper, "Who Left Open the Cookie Jar? A Comprehensive Evaluation of Third-Party Cookie Policies", detailed information about each web browser, tests to find out if a browser is vulnerable to exploits, and bug reports are linked on the research project's website.

 

The researchers created a test framework that they used to verify whether "all imposed cookie- and request-policies are correctly applied". They discovered that "most mechanisms could be circumvented"; all ad-blocking and anti-tracking browser extensions had at least one bypass flaw.

In this paper, we show that in the current state, built-in anti-tracking protection mechanisms as well as virtually every popular browser extension that relies on blocking third-party requests to either prevent user tracking or disable intrusive advertisements, can be bypassed by at least one technique

The researchers evaluated tracking protection functionality and a new cookie feature called same-site cookies that was introduced recently to defend against cross-site attacks.

 

Results for all tested browsers are shown in the table below. The researchers tested the default configuration of Chrome, Opera, Firefox, Safari, Edge, Cliqz, and Tor Browser, and configurations with third-party cookie blocking disabled, and if available, tracking protection functionality enabled.

 

tracking-cookies.png

 

Tor Browser is the only browser on the list that blocks third-party cookies by default. All browsers did not block cookies for certain redirects regardless of whether third-party cookies were blocked or tracking protection was enabled.

 

Chrome, Opera and other Chromium-based browsers that use the built-in PDF viewer have a major issue in regards to cookies.

Furthermore, a design flaw in Chromium-based browsers enabled a bypass for both the built-in third party cookie blocking option and tracking protection provided by extensions. Through JavaScript embedded in PDFs, which are rendered by a browser extension, cookie-bearing POST requests can be sent to other domains, regardless of the imposed policies.

Browser extensions for ad-blocking or anti-tracking had weaknesses as well according to the researchers. The list of extensions reads like the who is who of the privacy and content blocking world. It includes uMatrix and uBlock Origin, Adblock Plus, Ghostery, Privacy Badger, Disconnect, or AdBlock for Chrome.

 

The researchers discovered ways to circumvent the protections and reported several bugs to the developers. Some, Raymond Hill who is the lead developer of uBlock Origin and uMatrix, fixed the issues quickly.

 

At least one issue reported to browser makers has been fixed already. "Requests to fetch the favicon are not interceptable by Firefox extensions" has been fixed by Mozilla. Other reported issues are still in the process of being fixed, and a third kind won't be fixed at all.

 

web browser issues cookies

 

You can run individual tests designed for tested web browsers with the exception of Microsoft Edge on the project website to find out if your browser is having the same issues.

Closing Words

With more and more technologies being added to browsers, it is clear that the complexity has increased significantly. The research should be an eye opener for web browser makers and things will hopefully get better in the near future.

 

One has to ask whether some browser makers test certain features at all; Microsoft Edge not honoring the built-in setting to block third-party cookies is especially embarrassing in this regard. (via Deskmodder)

 

Now You: Do you use extensions or settings to protect your privacy better?

 

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Edited by vissha
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