cyberstrikeus CIS 10.4 — Ensure Only the Necessary SELinux Booleans are Enabled
Profile Applicability
- Caching Only Name Server Level 2
- Authoritative Name Server Level 2
Description
SELinux booleans allow or disallow specific behaviors. There are two boolean variables specific to the ISC BIND DNS server:
named_tcp_bind_http_port- Allow named to tcp bind http portnamed_write_master_zones- Allow named to write master zones
The named_tcp_bind_http_port would allow enabling the BIND statistics http channel which is not recommended. The named_write_master_zones allows BIND to update the master files, which is necessary when dynamic updates are performed, or the server is automatically maintaining DNSSEC digital signatures.
Rationale
Enabling only the necessary named related booleans provides a defense in depth approach, that will deny actions that are not in use or expected.
Impact
Not specified.
Audit Procedure
Perform the following steps to determine if the recommended state is implemented:
Use getsebool to verify the named_tcp_bind_http_port boolean has a value of off.
# getsebool named_tcp_bind_http_port
named_tcp_bind_http_port --> off
The named_write_master_zones boolean is not audited as many BIND servers will require the boolean to be enabled.
Remediation
Perform the following to implement the recommended state:
Disable the SELinux boolean using the setsebool command as shown below with the -P option to make the change persistent.
# setsebool -P named_tcp_bind_http_port off
Default Value
The default value for named_tcp_bind_http_port is off.
References
None listed in benchmark.
CIS Controls
| Controls Version | Control | IG 1 | IG 2 | IG 3 |
|---|---|---|---|---|
| v7 | 9.2 Ensure Only Approved Ports, Protocols and Services Are Running | N | Y | Y |
MITRE ATT&CK Mappings
| Tactic | Technique |
|---|---|
| Defense Evasion | T1562 Impair Defenses |
Profile
- Level 2 - Authoritative Name Server
- Level 2 - Caching Only Name Server