CVE-2026-18215: Keycloak-services: keycloak-services: microsoft external access-token exchange bypasses configured tenant

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-31 · updated 2026-09-16
Weakness: CWE-287

Description

Keycloak provides a way to let users log in using Microsoft accounts while restricting access to a specific organization (tenant). A flaw was discovered where this restriction is ignored when using the token exchange feature. This means an attacker with a valid Microsoft token from a completely different organization could gain access to the Keycloak realm, potentially accessing sensitive data or performing unauthorized actions.

Affected products

Red Hat build of Keycloak 26.4: all versions

References

https://access.redhat.com/errata/RHSA-2026:68277
https://access.redhat.com/errata/RHSA-2026:68278
https://access.redhat.com/security/cve/CVE-2026-18215
https://bugzilla.redhat.com/show_bug.cgi?id=2508309

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