First what is acropalypse?
Acropalypse is a vulnerability in Google’s markup editor (and Windows Snipping Tool). It allows an attacker to recover parts of a cropped or marked up image.
There are a couple specific steps you have to follow for the bug to happen.
- Take a screenshot
- Save screenshot
- Crop or markup screenshot in Google Markup or the Windows Snipping Tool
- Save screenshot with the same name as original screenshot
The bug is when you save the cropped screenshot with the same name, it overwrites the original file, but the markup tools are not resizing or truncating the file. Meaning that there is extra data in the screenshot.
For example in the following two screenshots, notice the size and dimensions
Here is the first screenshot
The second screenshot shows smaller dimensions because it was cropped, but the size is still the same.
Am I affected?
Potentially. Most images are reprocessed if they are being uploaded to a web service. Discord only started doing that in January. So if you have images on Discord before then, you may want to look into that.
You also have to specifically overwrite the original screenshot image. If you don’t normally save the image first you may be fine. Never hurts to check though.
Is macOS or iOS affected?
macOS and so presumably iOS, appear to properly resize the image after cropping has taken place. That would lead me to suspect that iOS and macOS devices are not vulnerable to a variant of apocalypse.
Twitter Post about acropalypse.