Google Pixel vulnerability allows bad actors to undo Markup screenshot edits and redactions

When Google began rolling out Android’s March security patch earlier this week, the company addressed a “High” severity vulnerability involving the Pixel’s Markup screenshot tool. Over the weekend, Simon Aarons and David Buchanan, the reverse engineers who discovered CVE-2023-21036, shared more information about the security flaw, revealing Pixel users are still at risk of their older images being compromised due to the nature of Google’s oversight.

In short, the “aCropalypse” flaw allowed someone to take a PNG screenshot cropped in Markup and undo at least some of the edits in the image. It’s easy to imagine scenarios where a bad actor could abuse that capability. For instance, if a Pixel owner used Markup to redact an image that included sensitive information about themselves, someone could exploit the flaw to reveal that information. You can find the technical details on Buchanan’s blog.

Introducing acropalypse: a serious privacy vulnerability in the Google Pixel's inbuilt screenshot editing tool, Markup, enabling partial recovery of the original, unedited image data of a cropped and/or redacted screenshot. Huge thanks to @David3141593 for his help throughout! pic.twitter.com/BXNQomnHbr

— Simon Aarons (@ItsSimonTime) March 17, 2023

According to Buchanan, the flaw has existed for about five years, coinciding with the release of Markup alongside Android 9 Pie in 2018. And therein lies the problem. While March’s security patch will prevent Markup from compromising future images, some screenshots Pixel users may have shared in the past are still at risk.

It’s hard to say how concerned Pixel users should be about the flaw. According to a forthcoming FAQ page Aarons and Buchanan shared with 9to5Google and The Verge, some websites, including Twitter, process images in such a way that someone could not exploit the vulnerability to reverse edit a screenshot or image. Users on other platforms aren’t so lucky. Aarons and Buchanan specifically identify Discord, noting the chat app did not patch out the exploit until its recent January 17th update. At the moment, it’s unclear if images shared on other social media and chat apps were left similarly vulnerable.

Google did not immediately respond to Engadget’s request for comment and more information. The March security update is currently available on the Pixel 4a, 5a, 7 and 7 Pro, meaning Markup can still produce vulnerable images on some Pixel devices. It’s unclear when Google will push the patch to other Pixel devices. If you own a Pixel phone without the patch, avoid using Markup to share sensitive images.

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