cis-bind-v100-4-4

name	cis-bind-v100-4-4
description	Restrict Access to All Key Files (Automated)
category	cis-bind
version	1.0
author	cyberstrike-official
tags	["cis","bind","dns","isc-bind","bind9","tsig"]
cis_id	4.4
cis_benchmark	CIS ISC BIND DNS Server 9.11 Benchmark v1.0.0
tech_stack	["bind","isc-bind","dns","linux"]
cwe_ids	[]
chains_with	[]
prerequisites	[]
severity_boost	{}

CIS 4.4 — Restrict Access to All Key Files

Profile Applicability

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

Description

The TSIG keys should be readable only by the named and root accounts. No other user accounts or groups should have read access. Note that BIND often creates a session key on startup for usage by nsupdate -l. Both the $BIND_HOME and $RUNDIR are included since the session key should also have the recommended permissions.

Rationale

The secret key protects the authenticity and integrity of TSIG communications and disclosure of a key would allow an attacker to perform the authenticated operations such as rndc administrative operations, zone transfers or dynamic updates.

Impact

Not specified in the PDF.

Audit Procedure

Perform the following to audit the recommendation:

• Find all of the TSIG key files in the $BIND_HOME and $RUNDIR directory, and capture the list to a file named key_file.txt in a tmp directory with the command below. If the RUNDIR is a subdirectory of BIND_HOME, which is typical for a chroot'ed directory, then some key files may be found twice. Duplicates are removed by the final sort command.

# find $BIND_HOME $RUNDIR -type f | xargs fgrep -l secret | sort -u > $TMPDIR/key_files.txt

• Check for appropriate ownership, group and permissions on the files with the following commands.

# find $(cat $TMPDIR/key_files.txt ) \! \( -user root -o -user named \) -ls
# find $(cat $TMPDIR/key_files.txt ) \! \( -group root -o -group named \) -ls
# find $(cat $TMPDIR/key_files.txt ) -perm /022

• There should be no output from the three find commands. Remove the temporary file when finished.

rm $TMPDIR/key_files.txt

Remediation

Perform the following for remediation:

• Use the command below to find secret key files. Review the list of key files, and delete any unused or unnecessary key files. Recreate the file list, after deleting any unused files.

# find $BIND_HOME $RUNDIR -type f | xargs fgrep -l secret | sort -u > $TMPDIR/key_files.txt

• Change the ownership, group and permissions on the key files.

# xargs -a $TMPDIR/key_files.txt chown -R root
# xargs -a $TMPDIR/key_files.txt chgrp -R named
# xargs -a $TMPDIR/key_files.txt chmod o-r