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TI-2026-39853 Aliases CVE-2026-55165GHSA-r9gp-7f88-9r54

Improper signature verification in Netflix lemur

Priority MEDIUM 55CWE-347Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Impact type
Security bypass
Confidentiality · integrity · availability
Low · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-347.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00154 4th percentileScored 2026-11-07
Fix Fixed lemur (Netflix): 1.9.2lemur (PyPI): 1.9.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
Netflixlemurbefore 1.9.21.9.2Patch availableCNA
—lemur (PyPI)before 1.9.21.9.2Patch availableGHSA-r9gp-7f88-9r54
  • lemur VendorNetflix Affected before 1.9.2 Fixed in 1.9.2 Patch available CNA
  • lemur (PyPI) Vendor— Affected before 1.9.2 Fixed in 1.9.2 Patch available GHSA-r9gp-7f88-9r54

Remediation

  • Fix · CNA lemur (Netflix) Fixed in 1.9.2
  • Fix · GHSA-r9gp-7f88-9r54 lemur (PyPI) Fixed in 1.9.2 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-55165
  2. 2026-10-03 Alias added: GHSA-r9gp-7f88-9r54

References

Other 4

  • TI-2024-04374 Path Traversal vulnerability via File Uploads in Genie CVSS 3.1CRITICAL 9.9
  • TI-2023-21044 Dispatch writes JWT tokens in error message CVSS 3.1CRITICAL 9.1
  • TI-2026-39854 Improper authorization in Netflix lemur CVSS 3.1CRITICAL 9.9
  • TI-2026-32272 Lemur: LDAP Filter Injection enables post-authentication privilege escalation CVSS 3.1HIGH 8.1
  • TI-2026-49966 Lemur: Unchecked `replaces[]` lets any user silence notifications and hijack auto-rotation for arbitrary certificates CVSS 3.1HIGH 8.1
  • TI-2026-49965 Missing authorization in Netflix lemur CVSS 3.1HIGH 7.7
See all 33 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences