Cis Ubuntu1804 V220 5 2 3 2

5.2.3.2 Ensure actions as another user are always logged

Profile Applicability

• Level 2 - Server
• Level 2 - Workstation

Description

sudo provides users with temporary elevated privileges to perform operations, either as the superuser or another user.

Rationale

Creating an audit log of users with temporary elevated privileges and the operation(s) they performed is essential to reporting. Administrators will want to correlate the events written to the audit trail with the records written to sudo's logfile to verify if unauthorized commands have been executed.

Audit

64 Bit systems

On disk configuration

Run the following command to check the on disk rules:

awk '/^ *-a *always,exit/ \
&&/ -F *arch=b64/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -S/ \
&&/ execve/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/' /etc/audit/rules.d/*.rules

Verify the output matches:

-a always,exit -F arch=b64 -C auid!=uid -F auid!=unset -S execve -k user_emulation
-a always,exit -F arch=b32 -C auid!=uid -F auid!=unset -S execve -k user_emulation

Running configuration

Run the following command to check loaded rules:

auditctl -l | awk '/^ *-a *always,exit/ \
&&/ -F *arch=b(32|64)/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -C/ \
&&/ execve/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)/'

Verify the output matches:

-a always,exit -F arch=b64 -S execve -C uid!=auid -F auid!=-1 -F key=user_emulation
-a always,exit -F arch=b32 -S execve -C uid!=auid -F auid!=-1 -F key=user_emulation

32 Bit systems

Follow the same procedures as for 64 bit systems and ignore any entries with b64.

Remediation

Create audit rules

Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor elevated privileges.

64 Bit systems

Example:

printf "
-a always,exit -F arch=b64 -C auid!=uid -F auid!=unset -S execve -k user_emulation
-a always,exit -F arch=b32 -C auid!=uid -F auid!=unset -S execve -k user_emulation
" >> /etc/audit/rules.d/50-user_emulation.rules

Load audit rules

Merge and load the rules into active configuration:

augenrules --load

Check if reboot is required:

if [[ $(auditctl -s | grep "enabled") =~ "2" ]]; then printf "Reboot required to load rules\n"; fi

32 Bit systems

Follow the same procedures as for 64 bit systems and ignore any entries with b64.

References

• NIST SP 800-53 Rev. 5: AU-3

CIS Controls

MITRE ATT&CK Mappings

Additional Information

Potential reboot required: If the auditing configuration is locked (-e 2), then augenrules will not warn in any way that rules could not be loaded into the running configuration. A system reboot will be required to load the rules into the running configuration.

System call structure: For performance (man 7 audit.rules) reasons it is preferable to have all the system calls on one line. However, your configuration may have them on one line each or some other combination.