What’s Vulnerable › Vulnerabilities

CVE-2026-9803: Keycloak: keycloak: denial of service via malformed authorization header

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-28 · updated 2026-10-26
• Weakness: CWE-125

Description

A flaw was found in Keycloak's ClientRegistrationAuth component. A remote unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with a malformed 'Authorization: Bearer' header to any client registration endpoint. This can lead to an ArrayIndexOutOfBoundsException, causing the server to return an HTTP 500 error and resulting in a Denial of Service (DoS) for the affected service.

Affected products

• Red Hat build of Keycloak 26.4: all versions

References

• https://access.redhat.com/errata/RHSA-2026:25097
• https://access.redhat.com/errata/RHSA-2026:25098
• https://access.redhat.com/errata/RHSA-2026:30049
• https://access.redhat.com/errata/RHSA-2026:30050
• https://access.redhat.com/security/cve/CVE-2026-9803
• https://bugzilla.redhat.com/show_bug.cgi?id=2482465

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