Boost proxy server security and defend against DoS attacks by blocking unsolicited packets or by using load balancers, as these actions could help reduce the impact the attack has on the server.
Unauthorized access attacks can be prevented by ensuring appropriate types of authorization are used to access the service and potentially by only allowing certain clients to access the proxy based on IPs. You could also authenticate the users of the proxy. Based on group membership, you could give them different authorizations to view different types of websites or vary their type of access.
Defend against attacks on proxy server software by using good management practices such as regularly updating software. You can also ensure that access to the management functionality is limited to only certain networks and uses strong access controls.
There are also attacks that use a proxy server on the Internet as a transit device to hide the originating source of the attack on your network. Blocking open or malicious proxy servers from accessing the network or servers is one way to prevent this type of attack from being successful. There are companies that maintain lists that can be used for this type of blocking, but take care to understand exactly what is being blocked and how the list is maintained. An example of a commercial block list is the one maintained by URLblacklist.com.
This was first published in May 2010