cis-bind9-v301-4-4

DevOps & Security

Restrict Access to All Key Files (Scored)

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Server_Software/Bind/CIS_ISC_BIND_DNS_Server_9.9_Benchmark_v3.0.1/cis-bind9-v301-4-4/SKILL.md

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CIS 4.4 — Restrict Access to All Key Files

Profile Applicability

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

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

None noted.

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.

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

Remove the temporary file.

rm $TMPDIR/key_files.txt

Default Value

Ownership, Group and Permissions are correct for any default key files.

References

None listed.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v6	14.4 - Protect Information with Access Control Lists	Y	Y	Y

MITRE ATT&CK Mappings

Tactic	Technique
Credential Access	T1552 - Unsecured Credentials
Credential Access	T1552.001 - Credentials In Files

Profile

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