Out-of-bounds Read in Red Hat Build Of Keycloak
CVE-2026-9803
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.007 (52.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 52nd percentile — 52.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.007 · change: +0.003
Affected products
- Red Hat Build Of Keycloak
- Red Hat Build Of Keycloak 26.4 — versions 26.4.13-1, 26.4-19
- Red Hat Build Of Keycloak 26.4.13
- Red Hat Build Of Keycloak 26.6 — versions 26.6-8, 26.6-6, 26.6.3-3
- Red Hat Build Of Keycloak 26.6.3
- Red Hat Build Of Keycloak 26.6.4
- Red Hat Build Of Keycloak
Weakness classification (CWE)
References
- access.redhat.com/security/cve/CVE-2026-9803 (vdb-entry, Vendor Advisory)
- bugzilla.redhat.com/show_bug.cgi (issue-tracking, Issue Tracking, Vendor Advisory)
- access.redhat.com/errata/RHSA-2026:25098 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:25097 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:30049 (vendor-advisory)
- access.redhat.com/errata/RHSA-2026:30050 (vendor-advisory)
Frequently asked questions
- What is CVE-2026-9803?
- CVE-2026-9803 is a medium-severity vulnerability in Red Hat Build Of Keycloak, classified under Out-of-bounds Read. CVSS score: 5.3/10. Published 2026-05-28.
- How severe is CVE-2026-9803?
- Medium severity. CVSS v3 base score is 5.3 out of 10.