4.1.3.13 Ensure file deletion events by users are collected

Audit

64 Bit systems

On disk configuration

Run the following command to check the on disk rules:

# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && awk "/^ *-a *always,exit/ \
&&/ -F *arch=b[2346]{2}/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -F *auid>=${UID_MIN}/ \
&&/ -S/ \
&&(/unlink/||/rename/||/unlinkat/||/renameat/) \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" /etc/audit/rules.d/*.rules \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"
}

Verify the output matches:

-a always,exit -F arch=b64 -S unlink,unlinkat,rename,renameat -F auid>=1000 -F auid!=unset -k delete
-a always,exit -F arch=b32 -S unlink,unlinkat,rename,renameat -F auid>=1000 -F auid!=unset -k delete

Running configuration

Run the following command to check loaded rules:

# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && auditctl -l | awk "/^ *-a *always,exit/ \
&&/ -F *arch=b[2346]{2}/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -F *auid>=${UID_MIN}/ \
&&/ -S/ \
&&(/unlink/||/rename/||/unlinkat/||/renameat/) \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"
}

Verify the output matches:

-a always,exit -F arch=b64 -S rename,unlink,unlinkat,renameat -F auid>=1000 -F auid!=-1 -F key=delete
-a always,exit -F arch=b32 -S unlink,rename,unlinkat,renameat -F auid>=1000 -F auid!=-1 -F key=delete

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 file deletion events by users.

64 Bit systems

Example:

# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && printf "
-a always,exit -F arch=b64 -S rename,unlink,unlinkat,renameat -F auid>=${UID_MIN} -F auid!=unset -F key=delete
-a always,exit -F arch=b32 -S rename,unlink,unlinkat,renameat -F auid>=${UID_MIN} -F auid!=unset -F key=delete
" >> /etc/audit/rules.d/50-delete.rules || printf "ERROR: Variable 'UID_MIN' is unset.\n"
}

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.