CVE-2026-46715 — Flask-Security-Too OAuth reauthentication freshness bypass via cross- user OAuth identity acceptance

Affected: pallets-eco Flask-Security-Too

Flask-Security-Too allows users to add security features to their Flask applicationa. Version 5.8.0's OAuth reauthentication flow can mark a session as fresh after verifying an OAuth account that belongs to a different user. If an attacker can operate an already-authenticated but stale victim session, they can complete OAuth verification using their own OAuth identity. The victim session is then treated as recently reauthenticated, allowing freshness-protected account actions to proceed. Version 5.8.1 contains a fix for this issue.

GHSA-97r5-pg8x-p63p — Flask-Security-Too OAuth reauthentication freshness bypass via cross- user OAuth identity acceptance

Affected: PyPI: Flask-Security-Too

### Summary

Flask-Security-Too 5.8.0's OAuth reauthentication flow can mark a session as fresh after verifying an OAuth account that belongs to a different user.

If an attacker can operate an already-authenticated but stale victim session, they can complete OAuth verification using their own OAuth identity. The victim session is then treated as recently reauthenticated, allowing freshness-protected account actions to proceed. This was reproduced against the built-in `/change-username` route.

### Details

The issue is in the OAuth verification callback.

`_oauth_response_common()` resolves the OAuth provider identity to a Flask-Security user:

- `flask_security/oauth_glue.py:101-108`

`oauth_verify_response()` then accepts any resolved user and updates the current session freshness timestamp:

- `flask_security/oauth_glue.py:182-214` - `flask_security/oauth_glue.py:201-204`

The missing check is that the OAuth-resolved user must match the current authenticated session user. In the failing case:

- current session user: `victim@example.com` - OAuth verified user: `attacker@example.com` - session marked fresh: yes

So the attacker is not logging in as the victim, but they are satisfying the victim session's reauthentication requirement with a different account.

### PoC

Tested version:

- `Flask-Security-Too 5.8.0` - tag `5.8.0` - commit `08288dff6907e413d848a16aaf43fc2c2b2a3b72`

Used a minimal Flask app with:…

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CVE-2026-46715 — Flask-Security-Too OAuth reauthentication freshness bypass via cross- user OAuth identity acceptance

GHSA-97r5-pg8x-p63p — Flask-Security-Too OAuth reauthentication freshness bypass via cross- user OAuth identity acceptance