CVE-2026-89058 Resteasy-core: resteasy: corsfilter reflects arbitrary origin with credentials under wildcard config
RESTEasy's CorsFilter reflects arbitrary origins with credentials when configured with wildcard, allowing malicious sites to read authenticated responses.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-89058?
CVE-2026-89058 is a high-severity vulnerability in Red Hat Build of Keycloak, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
A flaw was found in RESTEasy's CorsFilter, which, when configured to allow all origins ("*"), reflects the request's Origin header back in the Access-Control-Allow-Origin response together with Access-Control-Allow-Credentials: true. This permissive cross-origin policy allows a malicious website to make credentialed cross-origin requests and read authenticated responses from a victim's session, resulting in a loss of confidentiality.
Which versions are affected by CVE-2026-89058?
How do I fix CVE-2026-89058?
Apply the vendor's patch.
Is CVE-2026-89058 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-89058 exists.
Sources
Also known as CLEANSTART-2026-KS26010, CLEANSTART-2026-ZN77220, DEBIAN-CVE-2026-89058, GHSA-972r-f3fv-whm3, OESA-2026-4304, OESA-2026-4305 and 3 more.