PYSEC-2026-2589 Lemur: JWT verifier honors attacker-supplied alg, enabling ATO

Lemur 1.9.0: JWT verifier trusts attacker-supplied alg from token header — defense-in-depth gap; chain-dependent ATO with secret disclosure Vulnerability Summary Field | Value -- | -- Title | Lemur 1.9.0: JWT verifier trusts attacker-supplied alg from token header — defense-in-depth gap;...

PT-2026-52656

Name of the Vulnerable Software and Affected Versions Lemur versions prior to 1.9.0 Lemur version 1.9.0 Description The JWT verifier in the lemur/lemur/auth/service.py component trusts the alg header field from unverified tokens and passes it directly into the pyjwt.decode function via the...