Craft CMS Race condition in Token Service potentially allows for token usage greater than the token limit

A Time-of-Check-Time-of-Use (TOCTOU) race condition exists in Craft CMS’s token validation service for tokens that explicitly set a limited usage. The getTokenRoute() method reads a token’s usage count, checks if it’s within limits, then updates the database in separate non-atomic operations. By sending concurrent requests, an attacker can use a single-use impersonation token multiple times before the database update completes.

To make this work, an attacker needs to obtain a valid user account impersonation URL with a non-expired token via some other means and exploit a race condition while bypassing any rate-limiting rules in place.

For this to be a privilege escalation, the impersonation URL must include a token for a user account with more permissions than the current user.

References

https://github.com/craftcms/cms/commit/3e4afe18279951c024c64896aa2b93cda6d95fdf