4.1.3.19 Ensure kernel module loading unloading and modification is collected
Audit#
64 Bit systems
On disk configuration
Run the following commands to check the on disk rules:
# {
awk '/^ *-a *always,exit/ \
&&/ -F *arch=b[2346]{2}/ \
&&(/ -F auid!=unset/||/ -F auid!=-1/||/ -F auid!=4294967295/) \
&&/ -S/ \
&&(/init_module/ \
||/finit_module/ \
||/delete_module/ \
||/create_module/ \
||/query_module/) \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)' /etc/audit/rules.d/*.rules
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && awk "/^ *-a *always,exit/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -F *auid>=${UID_MIN}/ \
&&/ -F *perm=x/ \
&&/ -F *path=\/usr\/bin\/kmod/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" /etc/audit/rules.d/*.rules \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"
}
Verify the output matches:
-a always,exit -F arch=b64 -S init_module,finit_module,delete_module,create_module,query_module -F auid>=1000 -F auid!=unset -k kernel_modules
-a always,exit -F path=/usr/bin/kmod -F perm=x -F auid>=1000 -F auid!=unset -k kernel_modules
Running configuration
Run the following command to check loaded rules:
# {
auditctl -l | awk '/^ *-a *always,exit/ \
&&/ -F *arch=b[2346]{2}/ \
&&(/ -F auid!=unset/||/ -F auid!=-1/||/ -F auid!=4294967295/) \
&&/ -S/ \
&&(/init_module/ \
||/finit_module/ \
||/delete_module/ \
||/create_module/ \
||/query_module/) \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)'
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && auditctl -l | awk "/^ *-a *always,exit/ \
&&(/ -F *auid!=unset/||/ -F *auid!=-1/||/ -F *auid!=4294967295/) \
&&/ -F *auid>=${UID_MIN}/ \
&&/ -F *perm=x/ \
&&/ -F *path=\/usr\/bin\/kmod/ \
&&(/ key= *[!-~]* *$/||/ -k *[!-~]* *$/)" \
|| printf "ERROR: Variable 'UID_MIN' is unset.\n"
}
Verify the output includes:
-a always,exit -F arch=b64 -S
create_module,init_module,delete_module,query_module,finit_module -F auid>=1000 -F auid!=-1 -F key=kernel_modules
-a always,exit -S all -F path=/usr/bin/kmod -F perm=x -F auid>=1000 -F auid!=-1 -F key=kernel_modules
Symlink audit
Audit if the symlinks that kmod accepts is indeed pointing at it:
# S_LINKS=$(ls -l /usr/sbin/lsmod /usr/sbin/rmmod /usr/sbin/insmod /usr/sbin/modinfo /usr/sbin/modprobe /usr/sbin/depmod | grep -v " -> ../bin/kmod" || true) \
&& if [[ "${S_LINKS}" != "" ]]; then printf "Issue with symlinks: ${S_LINKS}\n"; else printf "OK\n"; fi
Verify the output states OK. If there is a symlink pointing to a different location it should be investigated.
Remediation#
Create audit rules
Edit or create a file in the /etc/audit/rules.d/ directory, ending in .rules extension, with the relevant rules to monitor kernel module modification.
64 Bit systems
Example:
# {
UID_MIN=$(awk '/^\s*UID_MIN/{print $2}' /etc/login.defs)
[ -n "${UID_MIN}" ] && printf "
-a always,exit -F arch=b64 -S
init_module,finit_module,delete_module,create_module,query_module -F auid>=${UID_MIN} -F auid!=unset -k kernel_modules
-a always,exit -F path=/usr/bin/kmod -F perm=x -F auid>=${UID_MIN} -F auid!=unset -k kernel_modules
" >> /etc/audit/rules.d/50-kernel_modules.rules || printf "ERROR: Variable 'UID_MIN' is unset.\n"
}
Load audit rules
Merge and load the rules into active configuration:
Check if reboot is required.