Darksat IT Security Forums

Bypassing firewalls with loose source routing is a rather effective way of bypassing security used by many hackers / crackers
Essentially the Ip address protocoll allows you to specify a specific hop on the way to or from a destination address.

eg send packet to Anthony from Mike but go via Bob's machine.
so for example if hacker X knows that access to a specific resource is limited to IP addresses inside a network he can spoff an IP address inside the network but use loose source routing to route the packet to his machine outside in order to gain access.

Many system admins still have loose source routing enabled in order for them to be able to check wheather specific machines on the network are up and running and are passing on requests, the problem often is that the firewalls will allow external packets through that claim to be originating from an internal machine.
The best defense against this is to set your firewall to reject any packets with loose source trace routing enabled.
Often however this technique is used to gain access to webservers which are normally facing the internat with no firewall.
eg, the attacker will spoof the ip 127.0.0.1 with loose source routing enabled back to his machine in the hopes of gaining access to the server.
So if you are running a webserver it is very important to make sure that you are protected against these types of attacks.