Keycloak GPI Prefix Check IDOR Enables Admin Access
CVE-2026-18203 Published on July 31, 2026
Keycloak-services: keycloak-services: group policy extendchildren matches sibling group path prefixes
A flaw was found in the group policy evaluation logic of Keycloak, an identity and access management solution. When a group policy is set to extend permissions to child groups, the system incorrectly uses a simple text-based prefix check to verify group membership. This allows a user who belongs to a different group with a similar starting name to bypass security checks and gain unauthorized access to administrative functions or protected resources.
Vulnerability Analysis
CVE-2026-18203 can be exploited with network access, and requires small amount of user privileges. 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, a high impact on integrity, and no impact on availability.
Timeline
Reported to Red Hat.
Made public.
Weakness Type
What is an AuthZ Vulnerability?
The software performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check. This allows attackers to bypass intended access restrictions.
CVE-2026-18203 has been classified to as an AuthZ vulnerability or weakness.
Products Associated with CVE-2026-18203
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Affected Versions
Red Hat Build of Keycloak: Red Hat Build of Keycloak: Red Hat Build of Keycloak: Red Hat Data Grid 8: Red Hat JBoss Enterprise Application Platform Expansion Pack: Red Hat Single Sign-On 7: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.