Authlib: JWS/JWT accepts unknown crit headers (RFC violation → possible authz bypass)

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2025-59420
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2025-09-22 18:15:46 UTC
Updated2026-10-19 16:10:00 UTC
DescriptionAuthlib 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Problem Types: CWE-345 | CWE-863 | CWE-345 CWE-345: Insufficient Verification of Data Authenticity | CWE-863 CWE-863: Incorrect Authorization

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Authlib Authlib All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Authlib Authlib affected < 1.6.4 Not specified

References

ReferenceSourceLinkTags
github.com/authlib/authlib/security/advisories/GHSA-9ggr-2464-2j32 [email protected] github.com Exploit, Vendor Advisory
github.com/authlib/authlib/commit/6b1813e4392eb7c168c276099ff7783b176479df [email protected] github.com Patch
lists.debian.org/debian-lts-announce/2025/10/msg00032.html af854a3a-2127-422b-91ae-364da2661108 lists.debian.org
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