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CVE-2026-9803

Keycloak: keycloak: denial of service via malformed authorization header

Published: May 28, 2026Updated: May 28, 2026 Sources: CVE List NVD
NVD MITRE
5.3CVSS
MEDIUM

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.

EPSS Score
N/A
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Workaround Only

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

Weaknesses

CWE-125

Affected Products

Red Hat Build of Keycloak
Red Hat

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Workaround Available

MITRE ATT&CK

1 technique
Collection
View detailed technique mapping

References

https://access.redhat.com/security/cve/CVE-2026-9803
access.redhat.com
https://bugzilla.redhat.com/show_bug.cgi?id=2482465
bugzilla.redhat.com

Timeline

Published
May 28, 2026
Last Updated
May 28, 2026

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