CVE WatchJul 15, 2026

CVE-2026-27962

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a JWK Header Injection vulnerability in a

CVSS

9.1

Critical

EPSS

0.5%

p42

KEV

—

Exploit Today

0-100

Published: Mar 16, 2026 · Last modified: Jul 15, 2026 · CWE-347

EPSS · 30d

0.5%EPSS · 30 days0.5%

2026-06-302026-07-16

Technical 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.

Official references

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