CVE-2026-9803

Keycloak: keycloak: denial of service via malformed authorization header

Published: May 28, 2026Updated: Jun 26, 2026 Sources: CVE List NVDCWE-125

5.3MEDIUM

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.

No summary for this CVE yet.

CVSS Vector Breakdown

Exploitability

AV:NAttack Vector

Network

AC:LAttack Complexity

Low

PR:NPrivileges Required

None

UI:NUser Interaction

None

Scope

S:UScope

Unchanged

Impact

C:NConfidentiality

None

I:NIntegrity

None

A:LAvailability

Low

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Weaknesses

CWE-125

Affected Products

Red Hat

commercial·USaka redhat

Red Hat build of Keycloak 26.4On-premWeb App

Web & CMS Plugins

Red Hat build of Keycloak 26.4.13On-prem

DevTools & CI

Red Hat build of Keycloak 26.6On-prem

Security Products / identity-access-mgmt

Red Hat build of Keycloak 26.6.3On-prem

Security Products / identity-access-mgmt

build of keycloakOn-prem

Operating Systems / linux-distro

Exploitability

Official Patch Available

Workaround Available

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Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

1 technique

Collection

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References

https://access.redhat.com/errata/RHSA-2026:25097

access.redhat.com

https://access.redhat.com/errata/RHSA-2026:25098

access.redhat.com

https://access.redhat.com/errata/RHSA-2026:30049

access.redhat.com

and 3 more references View all →

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