The proxy accepts gopher:// requests.
The proxy accepts gopher:// requests. Gopher is an old network protocol which predates HTTP and is nearly unused today. As a result, gopher-compatible software is generally less audited and more likely to contain security bugs than others. By making gopher requests, an attacker may evade your firewall settings by making connections to port 70 or may even exploit arcane flaws in this protocol to gain more privileges on this host (see the attached CVE ID for such an example).
Reconfigure your proxy to refuse gopher protocol requests.