{"id":"CVE-2026-55165","summary":"Lemur : JWT verifier trusts attacker-supplied alg from token header — defense-in-depth gap; chain-dependent ATO with secret disclosure","details":"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.","aliases":["GHSA-r9gp-7f88-9r54","PYSEC-2026-2589"],"modified":"2026-08-20T03:54:30.364998204Z","published":"2026-08-18T18:49:59.538Z","database_specific":{"cwe_ids":["CWE-347"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55165.json","cna_assigner":"GitHub_M"},"references":[{"type":"WEB","url":"https://github.com/Netflix/lemur/releases/tag/v1.9.2"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/55xxx/CVE-2026-55165.json"},{"type":"ADVISORY","url":"https://github.com/Netflix/lemur/security/advisories/GHSA-r9gp-7f88-9r54"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-55165"},{"type":"FIX","url":"https://github.com/Netflix/lemur/commit/89898e665beed044cf7bd5927dfaa484e55bf242"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/netflix/lemur","events":[{"introduced":"0"},{"fixed":"89898e665beed044cf7bd5927dfaa484e55bf242"},{"fixed":"4afd730de39fa9370f6c24ea8af7fcaa45430310"}],"database_specific":{"extracted_events":[{"introduced":"0"},{"fixed":"1.9.2"}],"source":["AFFECTED_FIELD","REFERENCES"]}}],"versions":["v1.9.1","v1.9.0","v1.8.2","v1.8.1","v1.8.0","v1.7.0","v1.6.0","v1.5.0","v1.4.0","v1.3.2","v1.3.1","v1.3.0","v1.2.0","v1.1.0","v1.0.0","v0.11.0","v0.10.0","v0.9.0","v0.8.1","0.8.0","0.7.0","0.6.0","0.5.0","0.4.0","0.3.0","0.2.2","0.2.1","0.2","0.1.5","0.1.4","0.1.3","0.1.2","0.1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-55165.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N"}]}