Description
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header Injection vulnerability in authlib's JWS implementation allows an unauthenticated attacker to forge arbitrary JWT tokens that pass signature verification. When key=None is passed to any JWS deserialization function, the library extracts and uses the cryptographic key embedded in the attacker-controlled JWT jwk header field. An attacker can sign a token with their own private key, embed the matching public key in the header, and have the server accept the forged token as cryptographically valid — bypassing authentication and authorization entirely. This issue has been patched in version 1.6.9.
Published: 2026-03-16
Score: 9.1 Critical
EPSS: < 1% Very Low
KEV: No
Impact: Authentication Bypass
Action: Immediate Patch
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Debian DLA Debian DLA DLA-4579-1 python-authlib security update
Github GHSA Github GHSA GHSA-wvwj-cvrp-7pv5 Authlib JWS JWK Header Injection: Signature Verification Bypass
History

Tue, 17 Mar 2026 21:00:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:a:authlib:authlib:*:*:*:*:*:*:*:*

Tue, 17 Mar 2026 13:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Tue, 17 Mar 2026 10:00:00 +0000

Type Values Removed Values Added
First Time appeared Authlib
Authlib authlib
Vendors & Products Authlib
Authlib authlib

Tue, 17 Mar 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

threat_severity

Important


Mon, 16 Mar 2026 20:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Mon, 16 Mar 2026 17:45:00 +0000

Type Values Removed Values Added
Description Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header Injection vulnerability in authlib's JWS implementation allows an unauthenticated attacker to forge arbitrary JWT tokens that pass signature verification. When key=None is passed to any JWS deserialization function, the library extracts and uses the cryptographic key embedded in the attacker-controlled JWT jwk header field. An attacker can sign a token with their own private key, embed the matching public key in the header, and have the server accept the forged token as cryptographically valid — bypassing authentication and authorization entirely. This issue has been patched in version 1.6.9.
Title Authlib JWS JWK Header Injection: Signature Verification Bypass
Weaknesses CWE-347
References
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-03-18T03:55:29.679Z

Reserved: 2026-02-25T03:24:57.792Z

Link: CVE-2026-27962

cve-icon Vulnrichment

Updated: 2026-03-16T19:11:55.751Z

cve-icon NVD

Status : Analyzed

Published: 2026-03-16T18:16:07.383

Modified: 2026-03-17T20:46:48.053

Link: CVE-2026-27962

cve-icon Redhat

Severity : Important

Publid Date: 2026-03-16T17:34:38Z

Links: CVE-2026-27962 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-03-24T10:50:06Z

Weaknesses