DNS Spoofing - Cache Poisoning Attacks

Cache Poisoning Attacks

Normally, a networked computer uses a DNS server provided by the computer user's organization or an Internet service provider (ISP). DNS servers are generally deployed in an organization's network to improve resolution response performance by caching previously obtained query results. Poisoning attacks on a single DNS server can affect the users serviced directly by the compromised server or indirectly by its downstream server(s) if applicable.

To perform a cache poisoning attack, the attacker exploits a flaw in the DNS software. If the server does not correctly validate DNS responses to ensure that they are from an authoritative source (for example by using DNSSEC) the server will end up caching the incorrect entries locally and serve them to other users that make the same request.

This technique can be used to direct users of a website to another site of the attacker's choosing. For example, an attacker spoofs the IP address DNS entries for a target website on a given DNS server, replacing them with the IP address of a server he controls. He then creates files on the server he controls with names matching those on the target server. These files could contain malicious content, such as a computer worm or a computer virus. A user whose computer has referenced the poisoned DNS server would be tricked into accepting content coming from a non-authentic server and unknowingly download malicious content.