CWE-280: Improper Handling of Insufficient Permissions or Privileges

Vanilla Forums version 2.1.a26 and possibly other versions are vulnerable to parameter manipulation via the "edit profile" page of authenticated users. An attacker with the ability to man-in-the-middle the connection using a proxy can alter the "UserID" of the user they wish to change allowing them to alter any profile setting and even change the email address.

An authenticated attacker can alter any profile setting including changing the email address for any user on the forum.

Update

The vendor has stated this vulnerability has been addressed in version 2.1a32. Users are advised to update to version 2.1a32 or higher.

Restrict access

As a general good security practice, only allow connections from trusted hosts and networks. Note that restricting access does not prevent XSS or CSRF attacks since the attack comes as an HTTP request from a legitimate user's host. Restricting access would prevent an attacker from accessing a web interface using stolen credentials from a blocked network location.