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Recursive DNS Server Detection

Medium

Synopsis

The remote name server allows recursive queries to be performed.

Description

It is possible to query the remote nameserver for third party names. If this is your internal nameserver, then disregard this warning. If the host allows these recursive queries via UDP, then the host can be used to 'bounce' Denial of Service attacks against another network or system.

Solution

Restrict recursive queries to the hosts that should use this nameserver (such as those of the LAN connected to it). If you are using BIND 8, you can do this by using the instruction 'allow-recursion' in the 'options' section of your named.conf. If you are using BIND 9, you can define a grouping of internal addresses using the 'acl' command. Then, within the options block, you can explicitly state: 'allow-recursion { hosts_defined_in_acl }'. If you are using another name server, consult its documentation.