CVE-2025-59420

Publication date 22 September 2025

Last updated 27 February 2026

Ubuntu priority

Cvss 3 Severity Score

Description

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.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
python-authlib	25.10 questing	Vulnerable
	25.04 plucky	Ignored end of life, was needs-triage
	24.04 LTS noble	Fixed 1.3.0-1ubuntu0.1~esm1
	22.04 LTS jammy	Fixed 0.15.5-1ubuntu0.1~esm1

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Severity score breakdown

Parameter	Value
Base score	7.5 · High
Attack vector	Network
Attack complexity	Low
Privileges required	None
User interaction	None
Scope	Unchanged
Confidentiality	None
Integrity impact	High
Availability impact	None
Vector	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

References

Related Ubuntu Security Notices (USN)

USN-8065-1
Authlib vulnerabilities
25 February 2026