CVE-2026-114617: Authlib: ID token can disable its own nonce validation via the nonce_supported claim
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, OpenIDMixin.parseidtoken() reads the noncesupported decision from the untrusted ID token being validated and sets the expected nonce to null when that claim is the JSON boolean false. In implicit and hybrid relying parties, or applications that directly accept externally supplied ID tokens, an attacker with a captured validly signed token can bypass the nonce-to-session binding and replay the victim's token into an attacker-controlled session. Plain authorization code flow is not affected, and the token must still pass signature, issuer, and audience validation. OpenIDMixin.parseidtoken() trusts noncesupported in both authlib/integrations/baseclient/syncopenid.py and authlib/integrations/baseclient/asyncopenid.py to disable the expected nonce. This issue is fixed in version 1.9.0.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Authlibto a version that resolves this vulnerability.Fixed in 1.9.0
Event History
Frequently Asked Questions
Which application flows are affected?
Implicit and hybrid relying-party flows are affected, as are applications that directly accept externally supplied ID tokens. Plain authorization code flow is not affected.
What does an attacker need to exploit this issue?
An attacker needs a captured, validly signed ID token and must replay it into an attacker-controlled session. The token must still pass signature, issuer, and audience validation.
Are applications using Authlib 1.9.0 affected?
No. The issue is fixed in Authlib version 1.9.0; versions prior to 1.9.0 are affected where the relevant token-handling flows are used.