It was found that Keycloak's Node.js adapter before version 4.4.0 did not properly verify the web token received from the server in its backchannel logout . An attacker with local access could use this to construct a malicious web token setting an NBF parameter that could prevent user access indefinitely.
CWE-287 - Improper Authentication
Improper (or broken) authentication attacks are widespread, and have accounted for many of the worst data breaches in recent years. Improper authentication attacks are a class of vulnerabilities where an attacker impersonates a legitimate user by exploiting weaknesses in either session management or credential management to gain access to the user’s account. This can result in disclosure of sensitive information, and can lead to system compromise, theft, identity theft, and fraud.