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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
NVD MITRE
EPSS Score
0.4%
Top 65.6%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
OpenVAS

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

AV:NAC:LPR:NUI:NS:UC:NI:NA:L
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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