CVE-2023-6563

An unconstrained memory consumption vulnerability was discovered in Keycloak. It can be triggered in environments which have millions of offline tokens (> 500,000 users with each having at least 2 saved sessions). If an attacker creates two or more user sessions and then open the “consents” tab of the admin User Interface, the UI attempts to load a huge number of offline client sessions leading to excessive memory and CPU consumption which could potentially crash the entire system.

Mitigation

There are three main options to prevent exploitation:

1. If you are using a reverse proxy, block the consents URL.
2. This option is less effective: remove the consents application tab from the account console theme.
3. This option has a significant negative impact on end users: entirely disable offline user profiles.