Janus Vulnerability on Android Allowed Modification of APKs Without Changing App Signature
Over the years, Android Security has really stepped up. However, while security has stepped up, another thing that has stepped up is the level of threats. A latest report found out that the Janus vulnerability, a name given to a vulnerability on Android, allowed users to modify APKs without even changing the app signature!
An app signature is basically a verification from the developer that the Google Play Store can run against it’s existing verification mechanism to confirm updates on app. An app will be updated only if the signatures match. The Janus vulnerability, which was recently discovered – allowed perpetrators to modify APKs without involving the app signature.
Here’s the technical aspect of the Janus Vulnerability:
Janus works by combining an unmodified APK file with a modified DEX executable, which doesn’t affect the app signature. The Android system would allow the installation, then start running code from the DEX header. Simply put, this would allow attackers to replace any app (ideally one with many permissions already granted, like system apps) with a malicious version.
This Janus vulnerability was reported to Google in late July and Google has finally issued a fix with the Android Security Patch dated 1st December.