CVE-2026-9803

Keycloak: keycloak: denial of service via malformed authorization header

Published May 28, 2026 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
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.

Remediation

Vendor Workaround

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-cpf7-j4cf-vqx4 Keycloak has an Out-of-bounds Read
History
Type Values Removed Values Added
CPEs cpe:/a:redhat:build_keycloak: cpe:/a:redhat:build_keycloak:26.6::el9
References
Type Values Removed Values Added
First Time appeared Redhat build Of Keycloak
CPEs cpe:2.3:a:redhat:build_of_keycloak:-:*:*:*:-:*:*:*
Vendors & Products Redhat build Of Keycloak
Type Values Removed Values Added
First Time appeared Redhat keycloak
Vendors & Products Redhat keycloak
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Keycloak: keycloak: denial of service via malformed authorization header
First Time appeared Redhat
Redhat build Keycloak
Weaknesses CWE-125
CPEs cpe:/a:redhat:build_keycloak:
Vendors & Products Redhat
Redhat build Keycloak
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
redhat
Published
Updated
Jun 26, 2026, 6:46 AM
Reserved
May 28, 2026, 4:02 AM
Status
Modified
Published
May 28, 2026, 6:16 AM
Modified
Oct 26, 2026, 12:10 PM
Severity
Moderate
Public date
May 28, 2026, 4:03 AM