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BIND-9X-001630 - The host running a BIND 9.x implementation must implement a set of firewall rules that restrict traffic on the DNS interface.

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Information

Configuring hosts that run a BIND 9.x implementation to only accept DNS traffic on a DNS interface allows a system firewall to be configured to limit the allowed incoming ports/protocols to 53/tcp and 53/udp. Sending outgoing DNS messages from a random port minimizes the risk of an attacker guessing the outgoing message port and sending forged replies.

The TCP/IP stack in DNS hosts (stub resolver, caching/resolving/recursive name server, authoritative name server, etc.) could be subjected to packet flooding attacks (such as SYNC and smurf), resulting in disruption of communication. By implementing a specific set of firewall rules that limit accepted traffic to the interface, these risk of packet flooding and other TCP/IP based attacks is reduced.

Solution

Configure the OS firewall to only allow incoming DNS traffic on ports 53/tcp and 53/udp.

Add the following rules to the host firewall rule set:

# iptables -A INPUT -i [DNS Interface] -p tcp --dport 53 -j ACCEPT
# iptables -A INPUT -i [DNS Interface] -p udp --dport 53 -j ACCEPT
# iptables -A INPUT -i [DNS Interface] -j DROP

Note: If the system is not using an IPTables firewall, the appropriate firewall rules that limit traffic to ports 53/tcp and 53/udp must be configured on the active firewall.

See Also

https://dl.dod.cyber.mil/wp-content/uploads/stigs/zip/U_BIND_9-x_V3R1_STIG.zip

Item Details

References: CAT|II, CCI|CCI-000366, Rule-ID|SV-272416r1124000_rule, STIG-ID|BIND-9X-001630, Vuln-ID|V-272416

Plugin: Unix

Control ID: b71ca7a3726334c810d27e3cad1ed1a254ed14530b7ba2e2209a6e6c98719c46