Token revocation record built from unverified JWT claims in AshAuthentication

Summary

Improper Verification of Cryptographic Signature vulnerability in team-alembic AshAuthentication allows a caller of the token revocation action to neutralise a revocation or write arbitrary rows into the token resource. AshAuthentication.TokenResource.RevokeTokenChange.change/3 reads the :token argument and decodes it with AshAuthentication.Jwt.peek/1, which delegates to Joken.peek_claims/1 and performs no signature check, unlike Jwt.verify/4. The jti, exp and sub claims it returns are written straight onto the revocation record, guarded only by byte_size(token) > 0. Because expires_at derives from the attacker-chosen exp, a forged copy of a genuine token that keeps the real jti but backdates exp yields a revocation row that is already expired: expunge_expired removes it and the genuine token passes revoked? again. Arbitrary jti and sub values can be inserted the same way. This issue affects ash_authentication: from 0.2.0 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.

Timeline

1. Sep 17, 2026, 1:09 PM UTCCVE published
2. Sep 17, 2026, 6:28 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: partial

3. Sep 17, 2026, 6:28 PM UTCRecord last updated

Affected versions

• ash_authentication

  From 0.2.0 · fixed in 4.15.0; From 5.0.0-rc.0 · fixed in 5.0.0-rc.14

• team-alembic/ash_authentication

  Version range not reported

References 6