Google Pixel Bug Lets You 'Uncrop' the Last Four Years of Screenshots

An anonymous reader quotes a report from Ars Technica: Back in 2018, Pixel phones gained a built-in screenshot editor called 'Markup' with the release of Android 9.0 Pie. The tool pops up whenever you take a screenshot, and tapping the app's pen icon gives you access to tools like crop and a few colored drawing pens. That's very handy assuming Google's Markup tool actually does what it says, but a new vulnerability points out the edits made by this tool weren't actually destructive! It's possible to uncrop or unredact Pixel screenshots taken during the past four years.

The bug was discovered by Simon Aarons and is dubbed 'Acropalypse,' or more formally CVE-2023-21036. There's a proof-of-concept app that can unredact Pixel screenshots at acropalypse.app, and it works! There's also a good technical write-up here by Aarons' collaborator, David Buchanan. The basic gist of the problem is that Google's screenshot editor overwrites the original screenshot file with your new edited screenshot, but it does not truncate or recompress that file in any way. If your edited screenshot has a smaller file size than the original -- that's very easy to do with the crop tool -- you end up with a PNG with a bunch of hidden junk data at the end of it. That junk data is made up of the end bits of your original screenshot, and it's actually possible to recover that data. While the bug was fixed in the March 2023 security update for Pixel devices, it doesn't solve the problem, notes Ars. 'There's still the matter of the last four years of Pixel screenshots that are out there and possibly full of hidden data that people didn't realize they were sharing.'

Read more of this story at Slashdot.