Out-of-bounds read in Red Hat build of Keycloak - CVE-2026-9803
Published: September 11, 2026
Vulnerability identifier: #VU148978
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-9803
CWE-ID: CWE-125
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to an out-of-bounds read in Keycloak\'s ClientRegistrationAuth component when processing a specially crafted POST request with a malformed Authorization: Bearer header at a client registration endpoint. A remote attacker can send a specially crafted POST request with a malformed Authorization: Bearer header to cause a denial of service.
The request can trigger an ArrayIndexOutOfBoundsException and an HTTP 500 error.
Affected software
Red Hat build of Keycloak
How to mitigate CVE-2026-9803
Install security update from vendor's website.
Red Hat build of Keycloak - addressed in versions 26.4.13, 26.6.3