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Keycloak CVE-2026-9803

| EUVD-2026-32719 MEDIUM
Out-of-bounds Read (CWE-125)
2026-05-28 secalert@redhat.com GHSA-cpf7-j4cf-vqx4
Buffer Overflow Denial Of Service Information Disclosure
5.3
CVSS 3.1
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CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

Lifecycle Timeline

1
Analysis Generated
May 28, 2026 - 06:32 vuln.today

DescriptionNVD

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.

AnalysisAI

Keycloak's ClientRegistrationAuth component can be crashed by a remote unauthenticated attacker through a specially crafted POST request bearing a malformed 'Authorization: Bearer' header, triggering an unhandled ArrayIndexOutOfBoundsException and returning HTTP 500 to all subsequent callers of the affected endpoint. The CVSS vector (AV:N/AC:L/PR:N/UI:N) confirms zero prerequisites for exploitation beyond network reachability, making any publicly exposed Keycloak client registration endpoint a viable target. …

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CVE-2026-9803 vulnerability details – vuln.today
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