Cis Bind9 V301 2 1

CIS 2.1 — Run BIND as a non-root User

Profile Applicability

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

Description

To start BIND you must execute it as the root user. After the initial startup, BIND has the ability to change to a non-root user, allowing it to drop the root privileges.

Rationale

The reason for configuring BIND to run as a non-root user is to limit the impact in case a future vulnerability is discovered and exploited. This is a common practice, which implements the principal of least privilege. This principle states that an entity, such as a service or user, should be granted only those specific privileges necessary to perform authorized actions. The server will still need to be started as root, but it should be configured to give up the root privilege after listening on port 53. The user ID under which named runs, needs to be created if it does not already exist and needs appropriate access to the DNS configuration and data files. Many systems including Red Hat Linux will come with a named user already created. Usage of the user and group id of 53 in the examples is arbitrary but is intended to be easier to recognize as it matches the listening port number.

Impact

Not Applicable

Audit Procedure

Perform the following to ensure the named account exists and has an appropriate non-root and non-user UID, and the -u named parameter is passed to named on startup.

1. Run the following commands to ensure the named account exists, and has been created with a UID greater than zero and less than MIN_UID.

# id named
uid=25(named) gid=25(named) groups=25(named)

# grep '^UID_MIN' /etc/login.defs
UID_MIN 1000

2. Verify that named service has been started and that the -u named option was passed when the daemon was executed, and that the user (first column) is equal to named.

# ps axu | grep named | grep -v 'grep'
named  423 0.0 1.0 236472 20512 ? Ssl Aug22 2:46 /usr/sbin/named -u named -t /var/named/chroot

Remediation

Create the named user and group if it does not already exist. Using a shell of /dev/null is best practice.

if ! id named; then
  groupadd -g 53 named
  useradd -m -u 53 -g 53 -c "BIND named" -d /var/named -s /dev/null named
fi 2>/dev/null

Add the -u named to the OPTIONS parameters in the /etc/sysconfig/named if not already present.

Default Value

The default named startup parameters include the -u named value.

References

Not Applicable

CIS Controls

MITRE ATT&CK Mappings

Profile

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