python-authlib: Authlib is a Python library which builds OAuth and OpenID Connect servers
CVE-2025-59420 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2025-59420, released September 22, 2025. It is not reported as exploited. Patch Radar priority: High.
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.4, Authlib’s JWS verification accepts tokens that declare unknown critical header parameters (crit), violating RFC 7515 “must‑understand” semantics. An attacker can craft a signed token with a critical header (for example, bork or cnf) that strict verifiers reject but Authlib accepts. In mixed‑language fleets, this enables split‑brain verification and can lead to policy bypass, replay, or privilege escalation. This issue has been patched in version 1.6.4.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| python-authlib · Debian 12.15 (bookworm) | 1.2.0-1+deb12u1 | DEBIAN-CVE-2025-59420 | Sep 22, 2025 |
| python-authlib · Debian 13.5 (trixie) | 1.6.0-1+deb13u1 | DEBIAN-CVE-2025-59420 | Sep 22, 2025 |
| python-authlib · Debian 14 | 1.6.4-1 | DEBIAN-CVE-2025-59420 | Sep 22, 2025 |
| python3-authlib · Ubuntu 22.04.1 LTS (jammy) | 0.15.5-1ubuntu0.1~esm1 | python3-authlib 0.15.5-1ubuntu0.1~esm1 | Oct 22, 2025 |
| python3-authlib · Ubuntu 24.04.5 LTS (noble) | 1.3.0-1ubuntu0.1~esm1 | python3-authlib 1.3.0-1ubuntu0.1~esm1 | Jan 8, 2026 |
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