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.
https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/