Vulnerability Description
Lemur manages TLS certificate creation. Prior to 1.9.2, the JWT verifier in lemur/auth/service.py:130-137 used fetch_token_header to read header_data["alg"] from an unverified token and passed that attacker-controlled value to decode_with_multiple_secrets. 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 LEMUR_TOKEN_SECRET would also permit forged HS256 tokens, although that disclosure is an independent prerequisite. The fix introduces the server-controlled LEMUR_TOKEN_ALGORITHMS allowlist and defaults it to HS256. This issue is fixed in version 1.9.2.
CVSS Score
MEDIUM
Related Weaknesses (CWE)
References
- https://github.com/Netflix/lemur/commit/89898e665beed044cf7bd5927dfaa484e55bf242
- https://github.com/Netflix/lemur/releases/tag/v1.9.2
- https://github.com/Netflix/lemur/security/advisories/GHSA-r9gp-7f88-9r54
- https://github.com/Netflix/lemur/security/advisories/GHSA-r9gp-7f88-9r54
FAQ
What is CVE-2026-55165?
CVE-2026-55165 is a vulnerability with a CVSS score of 4.8 (MEDIUM). Lemur manages TLS certificate creation. Prior to 1.9.2, the JWT verifier in lemur/auth/service.py:130-137 used fetch_token_header to read header_data["alg"] from an unverified token and passed that at...
How severe is CVE-2026-55165?
CVE-2026-55165 has been rated MEDIUM with a CVSS base score of 4.8/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-55165?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.