CVE-2026-27962
Authlib JWS JWK Header Injection: Signature Verification Bypass
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.
INFO
Published Date :
March 16, 2026, 6:16 p.m.
Last Modified :
March 17, 2026, 8:46 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | CRITICAL | [email protected] |
Solution
- Update Authlib to version 1.6.9 or later.
- Verify library integrity and dependencies.
- Monitor for suspicious token activity.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-27962.
| URL | Resource |
|---|---|
| https://github.com/authlib/authlib/commit/a5d4b2d4c9e46bfa11c82f85fdc2bcc0b50ae681 | Patch |
| https://github.com/authlib/authlib/releases/tag/v1.6.9 | Product Release Notes |
| https://github.com/authlib/authlib/security/advisories/GHSA-wvwj-cvrp-7pv5 | Exploit Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-27962 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-27962
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-27962 vulnerability anywhere in the article.
-
Daily CyberSecurity
Broken Keys: Critical Authlib Flaws Expose Millions to JWT Forgery and Padding Oracles
Security researchers exposed three critical vulnerabilities in Authlib, the widely used library for building OAuth and OpenID Connect servers. With over 86 million monthly downloads, the flaws in Auth ... Read more
The following table lists the changes that have been made to the
CVE-2026-27962 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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Initial Analysis by [email protected]
Mar. 17, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:authlib:authlib:*:*:*:*:*:*:*:* versions up to (excluding) 1.6.9 Added Reference Type GitHub, Inc.: https://github.com/authlib/authlib/commit/a5d4b2d4c9e46bfa11c82f85fdc2bcc0b50ae681 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/authlib/authlib/releases/tag/v1.6.9 Types: Product, Release Notes Added Reference Type GitHub, Inc.: https://github.com/authlib/authlib/security/advisories/GHSA-wvwj-cvrp-7pv5 Types: Exploit, Mitigation, Vendor Advisory -
New CVE Received by [email protected]
Mar. 16, 2026
Action Type Old Value New Value 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N Added CWE CWE-347 Added Reference https://github.com/authlib/authlib/commit/a5d4b2d4c9e46bfa11c82f85fdc2bcc0b50ae681 Added Reference https://github.com/authlib/authlib/releases/tag/v1.6.9 Added Reference https://github.com/authlib/authlib/security/advisories/GHSA-wvwj-cvrp-7pv5