cis-bind-v100-7-1

DevOps & Security

Do Not Define a Static Source Port (Automated)

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CIS 7.1 — Do Not Define a Static Source Port

Profile Applicability

Authoritative Name Server Level 1
Caching Only Name Server Level 1

Description

BIND can be configured to always use the same source port when communicating with other DNS servers. This capability is made possible through the query-source port option, and the query-source-v6 port option. It is recommended that the source port be omitted if the query-source option is used, or that the port be specified as a *, so that the port will not be a static port number.

Rationale

DNS attacks which involve spoofing a bogus DNS reply may require the attacker to guess the source port number of the request, if the attacker is unable to see the initial DNS query. Making the source port static makes the attack easier, as it eliminates the effort of getting the correct destination port number for the spoofed reply. Instead of a static source port, the port number should be selected randomly from the client ephemeral ports.

Impact

Not specified in the PDF.

Audit Procedure

Verify that a static port is not specified in a query-source option or a query-source-v6 option, using the command below.

$ egrep '^\W*query-source' $CONFIG_FILES | grep port
/etc/named.conf:     query-source address 10.1.45.53 port *;

If there is no output from the grep or if the port number is specified as *, then the configuration is compliant. Examples of a non-compliant configurations are shown below.

query-source port 1053;

query-source port-v6 53;

Remediation

Either remove the port specification from the query-source or the query-source-v6 option or use an * for the port number.

Default Value

The default is to not use a static source port for queries.

References

Not specified in the PDF.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v6	9 Limitation and Control of Network Ports, Protocols, and Services	Y	Y	Y
v7	9.2 Ensure Only Approved Ports, Protocols and Services Are Running	Y	Y	Y

MITRE ATT&CK Mappings

Tactic	Technique
Credential Access	T1557 - Adversary-in-the-Middle
Defense Evasion	T1562 - Impair Defenses
Command and Control	T1071.004 - Application Layer Protocol: DNS

Profile

Level 1 - Authoritative Name Server
Level 1 - Caching Only Name Server