CVE-2026-18203: Keycloak-services: keycloak-services: group policy extendchildren matches sibling group path prefixes
Vulnerability summary
CVE-2026-18203 is a medium (CVSS 6.5) Incorrect Authorization vulnerability in redhat build_of_keycloak. EPSS estimates a 0.31% chance of exploitation in the next 30 days, higher than 22.8% of scored vulnerabilities.
Timeline
- 31-07-2026PublishedVulnerability first disclosed.
- 31-08-2026Last modifiedVulnerability information updated.
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.
CVSS metrics
2 scores · 2 sources · 1 version- NVDNIST6.5MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
EPSS trend
Probability
0.31%
Chance of exploitation in the next 30 days
Percentile
23%
Versus all other CVEs
30-day change
Increase +0.13 pp
From 0.18% on 22-09-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Redhat1 product
1 vendor · 1 product