cis-ubuntu1604-v200-5-3-23

DevOps & Security

Ensure SSH MaxSessions is limited

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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-v200-5-3-23/SKILL.md

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CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 5.3.23

Description

The MaxSessions parameter Specifies the maximum number of open sessions permitted per network connection.

Rationale

To protect a system from denial of service due to a large number of concurrent sessions, use the rate limiting function of MaxSessions to protect availability of sshd logins and prevent overwhelming the daemon.

Audit Procedure

Command Line

Run the following command and verify that output MaxSessions is 10 or less:

sshd -T -C user=root -C host="$(hostname)" -C addr="$(grep $(hostname) /etc/hosts | awk '{print $1}')" | grep -i maxsessions

Expected Result

maxsessions 10

Run the following command and verify the output:

grep -Ei '^\s*MaxSessions\s+(1[1-9]|[2-9][0-9]|[1-9][0-9][0-9]+)' /etc/ssh/sshd_config

Nothing should be returned.

Remediation

Command Line

Edit the /etc/ssh/sshd_config file to set the parameter as follows:

MaxSessions 10

Default Value

MaxSessions 10

References

SSHD_CONFIG(5)

CIS Controls

Version 7

5.1 Establish Secure Configurations - Maintain documented, standard security configuration standards for all authorized operating systems and software.

Profile Applicability

Level 1 - Server
Level 1 - Workstation

Assessment Status

Automated