cis-bind-v100-2-8

DevOps & Security

Set Other Permissions Read-Only for All BIND Directories and Files (Automated)

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CIS 2.8 — Set Other Permissions Read-Only for All BIND Directories and Files

Profile Applicability

Authoritative Name Server Level 1
Caching Only Name Server Level 1

Description

All the directories and files in BIND home and run time directories should have other permissions set to not be writable. Configuration files should, of course, not be writable by named, and any run time files created by BIND will be owned by named and writable by the user. A chroot'ed tmp directory only needs to be writable by the named group. Therefore, there are no exceptions required.

Rationale

Restricting permissions on the 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 to modify configuration files.

Impact

Not specified.

Audit Procedure

Run the command below to ensure that all BIND directories and files are read-only for other. Note that a chroot'ed directory will have some special files which may need to be writable. Special files includes device files, like dev/null and a socket file for logging, but the -type f and type d restricts the find to just directories and regular files.

# find $BIND_HOME $RUNDIR -type f -perm /002

# find $BIND_HOME $RUNDIR -type d -perm /002

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 with the name $TMPDIR/write-files.txt
Review the purpose for the identified files and either delete them if the file is not needed, or change the permissions of the file to not be writable by group or other.
The following commands can be used to change the permissions of the appropriate files.

# find $BIND_HOME $RUNDIR -type f -perm /022 > $TMPDIR/write-files.txt
# xargs -a $TMPDIR/write-files.txt chmod go-w
# rm $TMPDIR/write-files.txt

Default Value

The default rpm install has all BIND directories and files without group or other write access.

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
Privilege Escalation	T1574 Hijack Execution Flow

Profile

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