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Chrome to patch loophole that allows sites to block Incognito mode users

Chrome to patch loophole that allows sites to block Incognito mode users

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The loophole lets sites block visitors they can’t track

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Stock imagery of the Chrome logo.
Illustration by Alex Castro / The Verge

Future versions of Chrome will fix a loophole that lets websites detect and block users who attempt to access them using the browser’s Incognito mode, reports 9to5Google.

As well as not storing any local records of your browsing history, Chrome’s Incognito mode stops websites from being able to track you using cookies. However, because so much of the web’s ad revenue relies on this tracking data, some sites, such as The Boston Globe and MIT Technology Review, prevent you from reading their articles if you visit them using this mode.

FileSystem API could eventually be removed entirely

Most sites do this by trying to use the “FileSystem” API, which is disabled while using Incognito mode because it allows permanent files to be created. However, recent commits to Chromium’s source code, which were first spotted by 9to5Google, show that the browser will soon trick websites into believing its FileSystem API is always operational.

When sites request to use the API when the browser is in Incognito mode in the future, Chrome will no longer return a conspicuous error. Instead, it will create a virtual file system in RAM. This will then get deleted at the end of your Incognito session, so that no permanent record can be created.

However, this workaround could end up being a short term fix before the FileSystem API is removed entirely. Internal design documents seen by 9to5Google suggest that the feature could be removed if Google discovers that it’s not seeing any legitimate use outside of discovering Incognito mode users.

The fix is currently aiming to arrive as an opt-in feature with Chrome 74, accessible via the “chrome://flags” menu of experimental features. That’s expected to arrive in April, before hopefully being turned on by default in Chrome 76. We’ve contacted Google for comment, and will update this piece if we hear a response.