cis-ubuntu1604-v200-4-1-11

DevOps & Security

Ensure use of privileged commands is collected

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CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Control 4.1.11

Profile

Level: 2 - Server
Level: 2 - Workstation
Assessment Status: Automated

Description

Monitor privileged programs (those that have the setuid and/or setgid bit set on execution) to determine if unprivileged users are running these commands.

Note: Reloading the auditd config to set active settings requires the auditd service to be restarted, and may require a system reboot.

Rationale

Execution of privileged commands by non-privileged users could be an indication of someone trying to gain unauthorized access to the system.

Impact

None.

Audit Procedure

Command Line

Run the following command replacing <partition> with a list of partitions where programs can be executed from on your system:

find <partition> -xdev \( -perm -4000 -o -perm -2000 \) -type f | awk '{print "-a always,exit -F path=" $1 " -F perm=x -F auid>=1000 -F auid!=4294967295 -k privileged" }'

Verify all resulting lines are a .rules file in /etc/audit/rules.d/ and the output of auditctl -l.

Note: The .rules file output will be auid!=-1 not auid!=4294967295.

Expected Result

All privileged commands should have corresponding audit rules.

Remediation

Command Line

To remediate this issue, the system administrator will have to execute a find command to locate all the privileged programs and then add an audit line for each one of them. The audit parameters associated with this are as follows:

-F path=" $1 " - will populate each file name found through the find command and processed by awk.
-F perm=x - will write an audit record if the file is executed.
-F auid>=1000 - will write a record if the user executing the command is not a privileged user.
-F auid!= 4294967295 - will ignore Daemon events

All audit records should be tagged with the identifier key "privileged".

Run the following command replacing <partition> with a list of partitions where programs can be executed from on your system:

find <partition> -xdev \( -perm -4000 -o -perm -2000 \) -type f | awk '{print "-a always,exit -F path=" $1 " -F perm=x -F auid>='"$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)"' -F auid!=4294967295 -k privileged" }'

Edit or create a file in the /etc/audit/rules.d/ directory ending in .rules and add all resulting lines to the file.

Example:

find / -xdev \( -perm -4000 -o -perm -2000 \) -type f | awk '{print "-a always,exit -F path=" $1 " -F perm=x -F auid>='"$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)"' -F auid!=4294967295 -k privileged" }' >> /etc/audit/rules.d/50-privileged.rules

Additional Information: Systems may have been customized to change the default UID_MIN. To confirm the UID_MIN for your system, run the following command:

awk '/^\s*UID_MIN/{print $2}' /etc/login.defs

If your systems' UID_MIN is not 1000, replace auid>=1000 with auid>=<UID_MIN for your system> in the Audit and Remediation procedures.

Default Value

By default, no audit rules are configured for privileged command usage.

References

CIS Ubuntu Linux 16.04 LTS Benchmark v2.0.0 - Section 4.1.11

CIS Controls

Controls Version	Control
v7	5.1 Establish Secure Configurations - Maintain documented, standard security configuration standards for all authorized operating systems and software.