What’s Vulnerable › Vulnerabilities
CVE-2026-114618: Authlib: Default JWT bearer grant accepts assertions for the wrong audience
- Severity: medium (CVSS 6.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: yes
- Published: 2026-10-22 · updated 2026-10-29
- Weakness: CWE-287
Description
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, the default RFC 7523 JWTBearerGrant.get_audiences() returns an empty list, causing JWTBearerGrant.verify_claims() to require only that an aud claim exists without matching the current authorization server. An attacker holding a legitimate assertion for another service can present it to a server that shares the signing key and uses the default grant, obtaining an access token across a trust boundary. Implementations that override get_audiences() with the server's valid audience identifiers are not affected. This issue is fixed in version 1.9.0.
Affected products
How to fix
Upgrade to a fixed version: authlib 1.9.0. Check the vendor advisory for mitigations.
References
- https://github.com/authlib/authlib/commit/e3bd41cb29dcfee434453b135ffb487884baeedf
- https://github.com/authlib/authlib/pull/945
- https://github.com/authlib/authlib/releases/tag/v1.9.0
- https://github.com/authlib/authlib/security/advisories/GHSA-fch4-3c6x-j4gc
- https://github.com/authlib/authlib/security/advisories/GHSA-fch4-3c6x-j4gc
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