CVE-2026-27962 — Authlib JWS JWK Header Injection: Signature Verification Bypass

Affected: authlib, Red Hat Quay 3.10, Red Hat Quay 3.14, Red Hat Quay 3.15, Red Hat Quay 3.16, Red Hat Quay 3.18, Red Hat Lightspeed Core, Red Hat Ansible Automation Platform 2, Red Hat OpenShift AI (RHOAI), Red Hat Satellite 6

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.

USN-8557-1 — python-authlib vulnerabilities

Affected: Ubuntu:Pro:22.04:LTS: python-authlib, Ubuntu:Pro:24.04:LTS: python-authlib, Ubuntu:Pro:26.04:LTS: python-authlib

Jay Neiva and Mauro Carrillo discovered that Authlib did not properly validate cryptographic keys embedded in JWT headers. An attacker could possibly use this issue to forge trusted tokens, resulting in authentication and authorization bypass. (CVE-2026-27962)

Jay Neiva and Mauro Carrillo discovered that Authlib incorrectly handled RSA1_5 encrypted tokens. An attacker could possibly use this issue to recover sensitive encrypted information, resulting in information disclosure. (CVE-2026-28490)

Jay Neiva and Mauro Carrillo discovered that Authlib did not properly reject unsupported cryptographic algorithms when validating OpenID Connect ID tokens. An attacker could possibly use this issue to bypass token integrity checks, resulting in authentication bypass. (CVE-2026-28498)

Johnny Deuss discovered that Authlib did not provide cross-site request forgery protection for the OAuth cache feature in its Starlette integration. An attacker could possibly use this issue to perform unauthorized OAuth actions, resulting in cross-site request forgery. This issue only affected Ubuntu 24.04 LTS and Ubuntu 26.04 LTS. (CVE-2026-41425)

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CVE-2026-27962 — Authlib JWS JWK Header Injection: Signature Verification Bypass

USN-8557-1 — python-authlib vulnerabilities