Rancher update on users can deny the service to the admin

Impact

A vulnerability has been identified within Rancher Manager where a missing server-side validation on the .username field in Rancher can allow users with update permissions on other User resources to cause denial of access for targeted accounts. Specifically:

• Username takeover: A user with permission to update another user’s resource can set its .username to "admin", preventing both the legitimate admin and the affected user from logging in, as Rancher enforces uniqueness at login time.
• Account lockout: A user with update permissions on the admin account can change the admin’s username, effectively blocking administrative access to the Rancher UI.

This issue enables a malicious or compromised account with elevated update privileges on User resources to disrupt platform administration and user authentication.

Note: The users with these permissions to modify accounts and resources are considered as privileged users. For more information, please consult Rancher Manger’s documentation about global permissions.

Please consult the associated MITRE ATT&CK - Technique - Account Access Removal for further information about this category of attack.

Patches

This vulnerability is addressed by adding a new check in the webhook which blocks modifying usernames after it has been set. If it's empty then the username can be set to a username not already in use, but after that it is immutable.

Patched versions of Rancher include releases v2.12.2, v2.11.6, v2.10.10 and v2.9.12.

Workarounds

If you can't upgrade to a fixed version, please make sure that you are only granting update permissions on users’ related resources to trusted users.

References

If you have any questions or comments about this advisory:

• Reach out to the SUSE Rancher Security team for security related inquiries.
• Open an issue in the Rancher repository.
• Verify with our support matrix and product support lifecycle.