CVE-2026-55165

Lemur manages TLS certificate creation. Prior to 1.9.2, the JWT verifier in lemur/auth/service.py:130-137 used fetchtokenheader to read headerdata["alg"] from an unverified token and passed that attacker-controlled value to decodewithmultiplesecrets. PyJWT 2.x rejects alg=none with the configured key, so the flaw is a defense-in-depth gap rather than a direct authentication bypass in the shipped configuration. The unpinned algorithm can become exploitable after an asymmetric-signing migration through algorithm confusion, and it weakens algorithm-based anomaly detection because the token chooses the recorded value. A separate disclosure of LEMURTOKENSECRET would also permit forged HS256 tokens, although that disclosure is an independent prerequisite. The fix introduces the server-controlled LEMURTOKENALGORITHMS allowlist and defaults it to HS256. This issue is fixed in version 1.9.2.