Wednesday, Jul 23, 2008    Text size: 

According to US-CERT, if an attacker can successfully conduct a cache poisoning attack, it may be able to cause a nameserver's clients to contact an incorrect, and possibly malicious, host. This may allow an attacker to obtain sensitive information or mislead users into believing they are visiting a legitimate website when they have in fact been redirected elsewhere.

This vulnerability may be of particular concern to high-traffic adult website operators that could be targeted in an attempt to steer visitors to rogue affiliate sites.

US-CERT is concerned that recent public postings regarding this vulnerability will provide attackers with the technical details that are required to exploit it, and as such are encouraging users to patch vulnerable systems immediately.

A document entitled "VU#800113 - Multiple DNS implementations vulnerable to cache poisoning" lists solutions to mitigate the risks, including placing the nameserver outside of the NAT/PAT device in the network infrastructure; configuring the NAT/PAT device to perform source port randomization; and configuring the NAT/PAT device to preserve the source port assigned by the nameserver.

While some of the patches implement source port randomization in the name server as a way to reduce the practicality of cache poisoning attacks, US-CERT cautions administrators that in infrastructures where nameservers exist behind Network Address Translation (NAT) and Port Address Translation (PAT) devices, port randomization in the nameserver may be overwritten by the NAT/PAT device and a sequential port address could be allocated, weakening the protection offered by source port randomization in the nameserver.

US-CERT will provide additional information as it becomes available.