CVE-2026-27962
Publication date 16 March 2026
Last updated 18 March 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| python-authlib | 25.10 questing |
Needs evaluation
|
| 24.04 LTS noble |
Needs evaluation
|
|
| 22.04 LTS jammy |
Needs evaluation
|
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
9.1 · Critical
|
| Attack vector | Network |
| Attack complexity | Low |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity impact | High |
| Availability impact | None |
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |