Keycloak OIDC Token Endpoint DoS via Excessively Long Scope Parameter
CVE-2026-4634 Published on April 2, 2026
Keycloak: keycloak: denial of service via excessive processing of openid connect scope parameters
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.
Vulnerability Analysis
CVE-2026-4634 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Timeline
Reported to Red Hat.
Made public. 10 days later.
Weakness Type
Excessive Platform Resource Consumption within a Loop
The software has a loop body or loop condition that contains a control element that directly or indirectly consumes platform resources, e.g. messaging, sessions, locks, or file descriptors.
Products Associated with CVE-2026-4634
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Affected Versions
Red Hat build of Keycloak 26.2:- Version 26.2.15-1 and below * is unaffected.
- Version 26.2-18 and below * is unaffected.
- Version 26.2-18 and below * is unaffected.
- Version 26.4.11-1 and below * is unaffected.
- Version 26.4-14 and below * is unaffected.
- Version 26.4-14 and below * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.