CVE-2026-4349 Duende IdentityServer4 Token Renewal Endpoint authorize improper authentication
Improper authentication in the token renewal endpoint allows remote attackers to bypass security checks, affecting unsupported versions of Duende IdentityServer4.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-4349?
CVE-2026-4349 is a medium-severity authentication bypass vulnerability in Duende IdentityServer4, published on 17 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A vulnerability was determined in Duende IdentityServer4 up to 4.1.2. The affected element is an unknown function of the file /connect/authorize of the component Token Renewal Endpoint. This manipulation of the argument id_token_hint causes improper authentication. It is possible to initiate the attack remotely. The attack is considered to have high complexity. The exploitability is described as difficult. This vulnerability only affects products that are no longer supported by the maintainer.
Weakness: CWE-287
Which versions are affected by CVE-2026-4349?
How do I fix CVE-2026-4349?
No fix has been published for CVE-2026-4349 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-4349 being exploited?
There is no known exploitation of CVE-2026-4349 in the wild and no public exploit code.
Sources
Also known as GHSA-46qm-5mvh-mmxr.