• The remote proxy server can be used to connect to arbitrary ports. <br/> The proxy allows everyone to perform HTTP requests to arbitrary ports, such as: <pre> GET http://www.acunetix.com:25 </pre> This may allow attackers to bypass your firewall and connect to sensitive ports like 23 (telnet), 25 (sendmail) using the proxy.

• Restrict proxy access to valid users and/or hosts. Deny access to non-authorized ports.

• • Wikipedia Open proxy
  • Wikipedia Web proxy
  • Setting up a Secure Proxy Server using Various Technologies

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• CWE-16

• Configuration Network Alert

• Apache Tomcat version older than 7.0.30
• Apache perl-status enabled
• Open X11 server
• Microsoft IIS WebDAV authentication bypass
• Apache configured to run as proxy