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Fencer Vulns
medium 6.5

CVE-2026-18203 json

Keycloak-services: keycloak-services: group policy extendchildren matches sibling group path prefixes

published 2026-07-31 3 mo ago modified 2026-11-06 2 d ago also EUVD-2026-51484

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits
0
none known

Summary

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.

Patch / fix

  • Red Hat Red Hat build of Keycloak 26.6 26.6-24, 26.6.8-2

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-18203 updated cvss 6.5

keycloak-services: keycloak-services: Group policy extendChildren matches sibling group path prefixes

  • Red Hat build of Keycloak 26.6 rhbk/keycloak-rhel9 26.6-24, rhbk/keycloak-rhel9-operator 26.6-24, rhbk/keycloak-operator-bundle 26.6.8-2
    fixed: vendor fix RHSA-2026:95762
  • Red Hat build of Keycloak 26.6.8
    fixed: vendor fix RHSA-2026:95761
  • Red Hat Data Grid 8 keycloak-services 23.0.7 Red Hat JBoss Enterprise Application Platform Expansion Pack keycloak-services 23.0.7 Red Hat Single Sign-On 7 keycloak-services 23.0.7
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
3 mo ago

Exploit prediction

0.39% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

Affected products

  • Red Hat Red Hat build of Keycloak 26.6
  • Red Hat Red Hat build of Keycloak 26.6.8
  • Red Hat Red Hat Data Grid 8
  • Red Hat Red Hat JBoss Enterprise Application Platform Expansion Pack
  • Red Hat Red Hat Single Sign-On 7

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.