Security researchers at Enclave have detailed a flaw in Microsoft Authenticator for Android, tracked as CVE-2026-80097. It let an app with zero permissions pose as an installed Microsoft app, such as Teams, and collect that app’s work-account tokens.
Microsoft’s September 8 advisory lists the fix as Authenticator 6.2606.4246. The researchers have now published how the attack worked. If you use Authenticator for a work account, make sure you’re on that build or later.
How the Microsoft Authenticator token attack worked
Enclave researcher Ofek Levin published the write-up, titled AuthMask, on October 23. He summarised the finding this way:
We found that an unprivileged Android app with zero permissions could impersonate any installed Microsoft first-party app and have the Microsoft Authenticator broker hand it that app’s tokens.
According to Enclave, Authenticator exposed an exported activity that any app on the phone could launch. The calling app then supplied its own claimed identity. That included a package name, client ID, redirect URI and requested scopes.
Authenticator checked that redirect URI against the signature of the app being impersonated. An attacker can read that signature from the Teams app already installed on the phone, so the check passed.
Enclave says Authenticator knew which package was really calling it but never used that for a trust decision. It then handed back access, refresh and ID tokens. In Enclave’s tests, those tokens opened the account’s mailbox, files and calendar with full delegated access.
That is an uncomfortable finding for an app whose whole job is security. Authenticator trusted the identity a caller claimed, even though it knew who was actually calling. Microsoft has fixed it, but this is the kind of check a sign-in broker is expected to get right.
Microsoft and Enclave disagree on user interaction
The two sides describe the attack differently. Microsoft’s advisory says an attacker would need to get a malicious app installed and convince the user to complete a sign-in flow in Authenticator. Its CVSS score also marks user interaction as required.
Enclave goes further. It says nothing was needed from the user beyond having Authenticator on the phone with a work account signed in. Microsoft’s advisory is the official assessment, so read Enclave’s version as the researchers’ own claim.
The researchers describe the attack against work accounts signed into Authenticator.
Severity and affected versions
Microsoft rates CVE-2026-80097 as Important, with a CVSS 3.1 base score of 8.6 and a temporal score of 7.5. It classes the bug as an elevation of privilege caused by improper authentication.
Affected builds run from version 6.0.0 up to, but not including, 6.2606.4246. The fix is delivered through Google Play.
Microsoft’s advisory lists the flaw as not exploited and rates exploitation as less likely. Microsoft released the advisory on September 8 and revised it on September 15.
How to check your Authenticator version
- Open the Google Play Store and search for Microsoft Authenticator.
- Tap Update if the option appears.
- Check the version number in the app’s settings or in the Play Store listing’s About this app section.
- Confirm it reads 6.2606.4246 or higher.
Enclave’s attack needs a malicious app on the phone first. Avoid sideloading apps from unknown sources, and remove any app you don’t recognise.
Android is tightening what apps can reach elsewhere too. Apps will lose easy write access to your contacts in 2027. Google has also added an opt-in scam protection mode to Google Messages.
Sources: Microsoft Security Response Center, Enclave, Google Play
