CVE-2026-103651: Concurrent Execution using Shared Resource with Improper Synchronization

MISP contains a vulnerability in its one-time password (OTP) authentication flow that allows replay of a consumed HOTP (paper) token and rewinding of the token counter.

The HOTP verification logic compared the submitted token against a counter value that was cached in the user's session at the time the password was entered, rather than against the authoritative counter stored in the database. Because the session-cached counter is not updated after a token is successfully consumed, an attacker who holds a valid session (password already submitted) can reuse a previously burned HOTP token. The stale cached counter still matches the replayed token, granting a second successful authentication and effectively rewinding the counter state.

Preconditions:

- The target user has HOTP (paper token) second-factor authentication enabled.

- The attacker possesses a valid session in which the password step has already been completed (the OTP step is pending).

- The attacker has access to at least one HOTP token value (e.g., a paper token list).

Security impact:

- Bypass of the second authentication factor, allowing unauthorized access to a user's MISP account.

- Corruption of the HOTP counter state, potentially invalidating subsequent legitimate tokens or enabling further replays.

Affected versions: <2.5.48.