CyberRota Analysis
AI-GeneratedThe vulnerability affects the JWT verifier in Lemur, where an unverified token's algorithm header can be manipulated, potentially leading to algorithm confusion during asymmetric-signing migrations. While not a direct authentication bypass under default configurations, it weakens security measures and could allow for forged tokens if the LEMUR_TOKEN_SECRET is also compromised. Organizations using Lemur prior to version 1.9.2 should prioritize upgrading to mitigate this risk.
Public Exploit Signal
A public exploit, PoC, GitHub repository or Metasploit reference was detected for this CVE.
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Original NVD 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.