Description
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.
Affected products
redhat: build of keycloak
References4
- access.redhat.com/security/cve/CVE-2026-18203 Vendor Advisory
- bugzilla.redhat.com/show_bug.cgi?id=2508291 Issue TrackingVendor Advisory
- access.redhat.com/errata/RHSA-2026:95761
- access.redhat.com/errata/RHSA-2026:95762
Metrics
- CVSS 3.1
-
6.5
MEDIUM
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N - EPSS — exploit probability
- 0% percentile: 34 · as of 13 November 2026
- CWE
- CWE-863
Could this be exploited in your environment?
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