cis-bind-v100-2-7

DevOps & Security

Set Group Read-Only for BIND Files and Non-Runtime Directories (Automated)

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CIS 2.7 — Set Group Read-Only for BIND Files and Non-Runtime Directories

Profile Applicability

Authoritative Name Server Level 1
Caching Only Name Server Level 1

Description

All of the BIND files and all of directories except the run-time directories into which BIND will create files should have group permissions set to not be writable. Any run-time files created by BIND will be owned by BIND, and therefore need not be group writable.

Rationale

Restricting permissions on the directories and files provides defense in depth and will reduce the probability of unauthorized modifications to important files. If there was a BIND vulnerability that allowed code execution as the named user, then the code would not be able create or modify configuration files.

Impact

Not specified.

Audit Procedure

Ensure the BIND_HOME and all the runtime directory variables are set as specified in the overview without a trailing slash after the directory name. Run the commands below to ensure that all BIND directories are read-only for group except for the expected run time directories where the named service will create files.

# find $BIND_HOME -type d -perm /020 | egrep -vx \
   $DYNDIR\|$SLAVEDIR\|$DATADIR\|$RUNDIR\|$LOGDIR\|$TMPDIR

# find $BIND_HOME -type f -perm /020

There should be no files listed in the output from the find commands.

Remediation

Perform the following:

Capture the output from the audit commands above into a file named write-dirs.txt
Review the purpose for the identified directories and either delete them if the directory is not needed, or change the permissions of the directory to not be writable by group or other.
The following command can be used to change the permissions of the directories that are appropriate.

xargs -a write-dirs.txt chmod g-w

Default Value

The default rpm install has the following non-runtime directories with group write access.

/var/named/

References

None listed.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v6	14.4 Protect Information With Access Control Lists	N	Y	Y
v7	14.6 Protect Information through Access Control Lists	Y	Y	Y

MITRE ATT&CK Mappings

Tactic	Technique
Defense Evasion	T1222 File and Directory Permissions Modification
Persistence	T1574 Hijack Execution Flow

Profile

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