How to Fix CVE-2026-4634: Red Hat build of Keycloak 26.2 (Bundle Sibling)
*By Sai Kiran Pandrala*
Last verified: 2026-05-25
| Severity | CVSS 7.5, High |
|---|---|
| Actively exploited? | No |
| Affected | Red Hat build of Keycloak 26.2 (26.2.15-1 < *); Red Hat build of Keycloak 26.2 (26.2-18 < *); Red Hat build of Keycloak 26.2 (26.2-18 < *) |
| Fixed in | Same patched build as CVE-2026-3872 |
| Type (CWE) | CWE-1050: Excessive Platform Resource Consumption within a Loop |
CVE-2026-4634 is a sibling vulnerability in the same Red Hat Red Hat build of Keycloak 26.2 advisory bundle as CVE-2026-3872. The same patched build closes every CVE in the bundle, so the remediation procedure for CVE-2026-4634 matches the primary write-up.
What is different about CVE-2026-4634?
A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in a Denial of Service (DoS) for the Keycloak server.
Impact is consistent with the bundle: a denial-of-service condition that crashes or hangs the affected service. The patched build closes every code path in the advisory in one update.
How to fix CVE-2026-4634
Apply the patched build per the primary write-up: How to Fix CVE-2026-3872.
For a quick check, confirm the running version of Red Hat build of Keycloak 26.2:
# Confirm the installed version via your package manager
dpkg -l | grep -i red # Debian/Ubuntu
rpm -qa | grep -i red # RHEL/CentOS/Rocky
Frequently asked questions
Is CVE-2026-4634 being actively exploited?
Not at the time of writing. It is not listed in CISA's Known Exploited Vulnerabilities catalog. That status can change, so monitor the vendor advisory and the KEV catalog if the system is exposed.
How severe is CVE-2026-4634?
CVSS rates it 7.5 (High). Use that score to set your patch priority alongside the other items in your queue.
Do I have to take Red Hat build of Keycloak 26.2 offline to apply the patch?
It depends on the deployment. High-availability or clustered installs can usually patch one node at a time with no full outage. Standalone installs typically need a short restart. Always follow the vendor's documented upgrade steps.
What if my vulnerability scanner still flags CVE-2026-4634 after I patch?
Re-run the scan after a service restart, then confirm the scanner's plugin set is up to date. Some scanners detect by banner version only and lag the official fix metadata by a release.
References
- Official vendor advisory: https://access.redhat.com/errata/RHSA-2026:6475
- NVD entry: https://nvd.nist.gov/vuln/detail/CVE-2026-4634
- CISA KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
- Primary write-up: How to Fix CVE-2026-3872
*Written by Sai Kiran Pandrala. Last verified 2026-05-25. Part of the Red Hat Red Hat build of Keycloak 26.2 advisory bundle. Full procedure at how-to-fix-cve-2026-3872.*