CVE-2026-107889: Keycloak-services: keycloak-services: stored xss on login page via kcsanitize bypass

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-09 · updated 2026-10-13
Weakness: CWE-79

Description

A flaw was found in the login theme rendering component of Keycloak. The issue occurs because the security filter responsible for cleaning user input can be bypassed, allowing a realm administrator to store malicious scripts in display fields. This could result in unauthorized JavaScript execution in the browsers of users visiting the login page, potentially leading to data exposure or session interference.

Affected products

Red Hat build of Keycloak 26.4: all versions

References

https://access.redhat.com/security/cve/CVE-2026-107889
https://bugzilla.redhat.com/show_bug.cgi?id=2548355

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