Vulnerability · Published Oct 22, 2026 · Assigned by GitHub_M

CVE-2026-114617Authlib: ID token can disable its own nonce validation via the nonce_supported claim

Medium 4.2

In plain English

A medium-severity security flaw in authlib from authlib. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 19% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)4.2Medium

Exploit odds (30 days)0.3%top 81.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, OpenIDMixin.parse_id_token() reads the nonce_supported 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.parse_id_token() trusts nonce_supported in both authlib/integrations/base_client/sync_openid.py and authlib/integrations/base_client/async_openid.py to disable the expected nonce. This issue is fixed in version 1.9.0.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	python-authlib	no fix listed	DEBIAN-CVE-2026-114617
Debian:13	python-authlib	no fix listed	DEBIAN-CVE-2026-114617
Debian:14	python-authlib	1.9.1-1	DEBIAN-CVE-2026-114617
PyPI	authlib	1.9.0	GHSA-c5mf-xmp2-59rc
PyPI	authlib	1.9.0	PYSEC-2026-4357
Ubuntu:26.10	python-authlib	no fix listed	UBUNTU-CVE-2026-114617

Affected products (as reported)

Vendor	Product	Versions
authlib	authlib	< 1.9.0

Weakness: CWE-294, CWE-807 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

References

https://github.com/authlib/authlib/security/advisories/GHSA-c5mf-xmp2-59rc x_refsource_CONFIRM
https://github.com/authlib/authlib/pull/949 x_refsource_MISC
https://github.com/authlib/authlib/commit/6563f6f7a8c2f71d2f85ee7511d72a4fbae3acc0 x_refsource_MISC
https://github.com/authlib/authlib/releases/tag/v1.9.0 x_refsource_MISC