cis-bind9-v301-4-1

name	cis-bind9-v301-4-1
description	Use TSIG Keys 256 Bits in Length (Scored)
category	cis-bind
version	3.0.1
author	cyberstrike-official
tags	["cis","bind","dns","isc-bind","bind9","tsig"]
cis_id	4.1
cis_benchmark	CIS ISC BIND DNS Server 9.9 Benchmark v3.0.1
tech_stack	["bind","isc-bind","dns","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS 4.1 — Use TSIG Keys 256 Bits in Length

Profile Applicability

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

Description

The TSIG secret keys used by the name server should be generated from a good source of entropy and should be at least 256 bits in length.

Rationale

Weak cryptographic keys may allow cryptographic attacks to discover the key value, through repeated guesses. A strong HMAC key requires a good source of entropy and at least 256 bits in length.

Impact

None noted.

Audit Procedure

To check if the secret key is at least 256 bits long before encoding then the base64 encoded value should be 44 characters long or longer with the padding and a trailing =. To easily count the number of characters, copy the key value into the quoted value in the command below.

$ echo -n "ezoZopbE4Q73HShuFYlf3FRvLWjtNXI5fd0TeQAYOug=" | wc -c
44

Remediation

For remediation, replace any keys which are too short with a securely generated key with a length of 256 or 512. The dnssec-keygen command below can be used to generate a key.

$ dnssec-keygen -a HMAC-SHA256 -b 256 -n HOST ns1-ns2.cisecurity.org.

$ cat Kns1-ns2.cisecurity.org.+163+21730.key
ns1-ns2.cisecurity.org. IN KEY 512 3 163
ezoZopbE4Q73HShuFYlf3FRvLWjtNXI5fd0TeQAYOug=

Default Value

The rndc key is generated as 128 bits during bind-utils package install, while the nsupdate session key is dynamically generated with a length of 256 bits.

References

None listed.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v6	14.2 - Encrypt All Sensitive Information Over Less-trusted Networks	Y	Y	Y

MITRE ATT&CK Mappings

Tactic	Technique
Credential Access	T1110 - Brute Force
Lateral Movement