Medium severity · published May 28, 2026
CVE-2026-9803
Keycloak: keycloak: denial of service via malformed authorization header
5.3
CVSS
0.4%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 36% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
RH
Red Hat build of Keycloak 26.4 · Red Hat
All versions, or not specified · source: vendor
RH
Red Hat build of Keycloak 26.6 · Red Hat
All versions, or not specified · source: vendor
BO
Build OF Keycloak · Redhat
All versions, or not specified · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-9803
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-9803
access.redhat.com
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
https://access.redhat.com/errata/RHSA-2026:30050
Vendor Advisory
https://access.redhat.com/security/cve/CVE-2026-9803
Issue Tracking
https://bugzilla.redhat.com/show_bug.cgi?id=2482465
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