Six Microsoft 365 Android apps contain an identical flaw that could risk billions of downloads being compromised.
The findings, shared exclusively with SecurityWeek ahead of the expected public release of the research on Tuesday, were uncovered by Enclave, an AI-powered exploitable bug hunter. It is nothing more than a single debug flag being left in the production code of Word, PowerPoint, Excel, Microsoft 365 Copilot, Microsoft Loop and OneNote for Android. Someone left debug mode enabled in production: – set IsDebugMode(true). This was enabled across all six apps, but was not enabled in other Microsoft (MS) apps such as Teams. These were not affected by any consequent potential exploitation attempt.
The effect of such debug flags varies. Sometimes the purpose is simply to affect logging or to test output. “This one changed the behavior around account access token sharing,” explains Enclave reporting its findings. “With debug mode enabled, the protection that should have blocked untrusted apps from receiving tokens was skipped.”
Microsoft’s intention is to allow easy passage for its authorized customers from one MS app to another MS app on the same device, without requiring new login authorization from the Android user each time. So, the code in the apps is designed to pass access tokens to the other MS apps – but crucially, not do so for any other Android app. The effect of this debug flag omitted the restriction on non-MS apps, and the result was that Android MS access tokens were handed to any Android app that requested them.
