cis-ubuntu1604-v200-4-2-1-6

DevOps & Security

Ensure remote rsyslog messages are only accepted on designated log hosts

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_16.04_LTS_Benchmark_v2.0.0/cis-ubuntu1604-v200-4-2-1-6/SKILL.md

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CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 4.2.1.6

Profile

Level: 1 - Server
Level: 1 - Workstation
Assessment Status: Manual

Description

By default, rsyslog does not listen for log messages coming in from remote systems. The ModLoad tells rsyslog to load the imtcp.so module so it can listen over a network via TCP. The InputTCPServerRun option instructs rsyslogd to listen on the specified TCP port.

Rationale

The guidance in the section ensures that remote log hosts are configured to only accept rsyslog data from hosts within the specified domain and that those systems that are not designed to be log hosts do not accept any remote rsyslog messages. This provides protection from spoofed log data and ensures that system administrators are reviewing reasonably complete syslog data in a central location.

Note: The $ModLoad imtcp line can have the .so extension added to the end of the module, or use the full path to the module.

Impact

None.

Audit Procedure

Run the following commands and verify the resulting lines are:

Not commented on designated log hosts
Commented or not present on all others

Command Line

Run the following command and verify the output for $ModLoad imtcp:

grep '$ModLoad imtcp' /etc/rsyslog.conf /etc/rsyslog.d/*.conf

Output for designated log hosts:

$ModLoad imtcp

Output for systems that are not log hosts: (No output is also acceptable)

# $ModLoad imtcp

Run the following command and verify the output for $InputTCPServerRun:

grep '$InputTCPServerRun' /etc/rsyslog.conf /etc/rsyslog.d/*.conf

Output for designated log hosts:

$InputTCPServerRun 514

Output for systems that are not log hosts: (No output is also acceptable)

# $InputTCPServerRun 514

Expected Result

On designated log hosts, $ModLoad imtcp and $InputTCPServerRun 514 should be uncommented. On all other systems, these lines should be commented out or not present.

Remediation

For hosts that are designated as log hosts, edit the /etc/rsyslog.conf file and un-comment or add the following lines:

Command Line

# Add or uncomment in /etc/rsyslog.conf for designated log hosts:
$ModLoad imtcp
$InputTCPServerRun 514

For hosts that are not designated as log hosts, edit the /etc/rsyslog.conf file and comment or remove the following lines:

# Comment out in /etc/rsyslog.conf for non-log hosts:
# $ModLoad imtcp
# $InputTCPServerRun 514

Run the following command to reload the rsyslogd configuration:

systemctl restart rsyslog

Default Value

rsyslog does not accept remote messages by default.

References

See the rsyslog(8) man page for more information.

CIS Controls

Controls Version	Control	IG 1	IG 2	IG 3
v7	9.2 Ensure Only Approved Ports, Protocols and Services Are RunningEnsure that only network ports, protocols, and services listening on a system with validated business needs, are running on each system.