MISP HOTP Token Replay via Stale Session-Cached Counter Allows Second-Factor Authentication Bypass

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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.

Source published

1 Oct 2026 07:34:02 UTC

Source modified

1 Oct 2026 15:32:08 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 4.0 · 7.6 CVSS:4.0/AV:N/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N