Squiz Matrix CMS 6.20 is vulnerable to an Insecure Direct Object Reference caused by failure to correctly validate authorization when submitting a request to change a user's contact details. NOTE: this is disputed by both the vendor and the original discoverer because it is a site-specific finding, not a finding about the Squiz Matrix CMS product.
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.