CVE-2026-4634 Keycloak: keycloak: denial of service via excessive processing of openid connect scope parameters
An unauthenticated attacker can cause a Denial of Service on Keycloak by sending a specially crafted POST request with an excessively long scope parameter.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-4634?
CVE-2026-4634 is a high-severity denial of service vulnerability in Redhat Build of Keycloak, published on 2 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-1050
Which versions are affected by CVE-2026-4634?
3 open source packages ship an affected version, including org.keycloak:keycloak-services and keycloak. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
org.keycloak:keycloak-services Maven | All versions | 26.5.7 |
org.keycloak:keycloak-services Maven | All versions | 26.5.7 |
keycloak Bitnami | From 26.2.0 | 26.2.1, 26.3.0, 26.4.1, 26.5.0 |
Products include Redhat Build of Keycloak.
How do I fix CVE-2026-4634?
Upgrade org.keycloak:keycloak-services to 26.5.7 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-4634 being exploited?
There is no known exploitation of CVE-2026-4634 in the wild and no public exploit code.
Other vulnerabilities in Redhat Build of Keycloak
- CVE-2026-15572 Keycloak-services: keycloak-services: dcr protocol mapper type-swap policy bypass allows privilege escalation
- CVE-2026-3047 Keycloak SAML Broken has Authentication Bypass by Primary Weakness
- CVE-2026-15573 Keycloak-services: keycloak-services: authorization bypass via unnormalized uri matching in pathmatcher
- CVE-2026-16102 Keycloak-services: keycloak-services: default dcr policy allows role forgery via user property mappers
- CVE-2026-1609 Org.keycloak/keycloak-quarkus-server: keycloak: unauthorized access via jwt authorization grant with disabled users
Sources
Also known as BIT-keycloak-2026-4634, ECHO-5745-1868-1f70, GHSA-h4wv-g838-66g3, MINI-p6f6-m593-g9m8, MINI-r7hv-4mc7-v5jm.