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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Red Hat | Red Hat build of Keycloak 26.4 | — | — |
| Red Hat | Red Hat build of Keycloak 26.4.13 | — | — |
| Red Hat | Red Hat build of Keycloak 26.6 | — | — |
| Red Hat | Red Hat build of Keycloak 26.6.3 | — | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | keycloak-26.5 +2 | No fix yet | — |
Affected packages
| Ecosystem | Package | Affected | Fixed | Record |
|---|---|---|---|---|
| Maven | org.keycloak:keycloak-services | <= 26.4.7 | — | GHSA-cpf7-j4cf-vqx4 |
| Maven | org.keycloak:keycloak-services | >= 26.5.0, < 26.6.3 | 26.6.3 | GHSA-cpf7-j4cf-vqx4 |
Advisories 1
- WID-SEC-2026-1708 Keycloak: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 8, 2026
References
- RHSA-2026:25097 vendor-advisory
- RHSA-2026:25098 vendor-advisory
- RHSA-2026:30049 vendor-advisory
- RHSA-2026:30050 vendor-advisory
- https://access.redhat.com/security/cve/CVE-2026-9803 vdb-entry
- RHBZ#2482465 issue-tracking