laurel - Advice for writing Audit rulesets for use with laurel(8)(7) System Administration Utilities laurel - Advice for writing Audit rulesets for use with laurel(8)(7)

laurel-audit-rules - Advice for writing Audit rulesets for use with laurel(8)

This page contains suggestions for Linux Audit rulesets that are useful to aid in detecting common attacker’s tactics.

It is not possible for /auditctl(8)/ ro load file watches for files or directories that are not present. Depending on the rule set, it will spam possibly lots of error messages to standard error. The specific file watches are not installed, but those error messages can be ignored otherwise.

-w /etc/group           -p wa -k wr_group
-w /etc/passwd          -p wa -k wr_passwd
-w /etc/shadow          -p wa -k wr_passwd
-w /etc/pam.conf        -p wa -k wr_pam
-w /etc/pam.d/          -p wa -k wr_pam
-w /etc/ssh/sshd_config -p wa -k wr_sshd
-w /etc/sudoers         -p wa -k wr_sudo
-w /etc/sudoers.d       -p wa -k wr_sudo
    

-w /etc/crontab              -p wa -k wr_cron
-w /etc/cron.d/              -p wa -k wr_cron
-w /etc/cron.daily/          -p wa -k wr_cron
-w /etc/cron.hourly/         -p wa -k wr_cron
-w /etc/cron.monthly/        -p wa -k wr_cron
-w /etc/cron.weekly/         -p wa -k wr_cron
-w /etc/cron.yearly/         -p wa -k wr_cron
-w /etc/cron.allow           -p wa -k wr_cron
-w /etc/cron.deny            -p wa -k wr_cron
-w /var/spool/cron/crontabs/ -p wa -k wr_cron
-w /etc/at.allow             -p wa -k wr_cron
-w /etc/at.deny              -p wa -k wr_cron
-w /var/spool/cron/atjobs/   -p wa -k wr_cron

Systemd also has cron-like timer mechanism. udev triggers have also been abused for persistence. Note that watching the files in /etc is not sufficient.

-w /etc/systemd     -p wa -k wr_systemd
-w /lib/systemd     -p wa -k wr_systemd
-w /usr/lib/systemd -p wa -k wr_systemd
-w /etc/udev        -p wa -k wr_systemd
-w /lib/udev        -p wa -k wr_systemd
-w /usr/lib/udev    -p wa -k wr_systemd
    

-w /lib/ld-linux.so.2          -p wa -k wr_ldso
-w /lib64/ld-linux-x86-64.so.2 -p wa -k wr_ldso
-w /lib/ld-musl-x86_64.so.1    -p wa -k wr_ldso
-w /lib/ld-musl-i386.so.1      -p wa -k wr_ldso
-w /etc/ld.so.conf             -p wa -k wr_ldso
-w /etc/ld.so.conf.d           -p wa -k wr_ldso
-w /etc/ld.so.preload          -p wa -k wr_ldso
    

-w /etc/selinux         -p wa -k wr_selinux
-w /usr/share/selinux   -p wa -k wr_selinux
-w /usr/libexec/selinux -p wa -k wr_selinux
-w /etc/apparmor.d              -p wa -k wr_apparmor
-w /usr/lib/apparmor            -p wa -k wr_apparmor
-w /usr/share/apparmor          -p wa -k wr_apparmor
-w /usr/share/apparmor-features -p wa -k wr_apparmor
    

-w /etc/modprobe.conf -p wa -k wr_modules
-w /etc/modprobe.d/   -p wa -k wr_modules
-w /lib/modules/      -p wa -k wr_modules
    

-w /etc/audit/        -p wa -k wr_audit_config
-w /etc/libaudit.conf -p wa -k wr_audit_config
-w /etc/audisp/       -p wa -k wr_audit_config
-w /etc/laurel/       -p wa -k wr_laurel_confg
    

-w /sbin/auditctl   -p x -k wr_audit_tools
-w /sbin/auditd     -p x -k wr_audit_tools
-w /usr/sbin/laurel -p x -k wr_audit_tools

Adding context to system service activities is useful because together with Laurel’s process labels (label-process.label-keys, label-process.propagate-labels), it enables more accurate detection rules that can help recognize benign system management activity.

-w /usr/sbin/sshd -p x -k sshd
-w /usr/bin/yum                -p x -k pkg_mgmt
-w /usr/bin/rpm                -p x -k pkg_mgmt
-w /usr/bin/dnf                -p x -k pkg_mgmt
-w /usr/bin/dpkg               -p x -k pkg_mgmt
-w /usr/bin/apt                -p x -k pkg_mgmt
-w /usr/bin/apt-get            -p x -k pkg_mgmt
-w /usr/bin/apt-key            -p x -k pkg_mgmt
-w /usr/bin/apt-add-repository -p x -k pkg_mgmt
-w /usr/bin/aptitude           -p x -k pkg_mgmt
-w /usr/bin/aptitude-curses    -p x -k pkg_mgmt
-w /usr/bin/wajig              -p x -k pkg_mgmt
-w /usr/bin/snap               -p x -k pkg_mgmt
-w /usr/sbin/yast2             -p x -k pkg_mgmt
-w /usr/bin/zypper             -p x -k pkg_mgmt
-w /usr/bin/containerd        -p x -k container
-w /usr/bin/podman            -p x -k container
-w /usr/bin/runc              -p x -k container
-w /usr/bin/dockerd           -p x -k container
-w /usr/bin/docker            -p x -k container
-w /usr/bin/docker-containerd -p x -k container
-w /usr/bin/docker-runc       -p x -k container
-w /usr/sbin/cron -p x -k sched_task
-w /usr/sbin/atd  -p x -k sched_task
-w /usr/sbin/httpd              -p x -k apache-httpd
-w /usr/local/apache2/bin/httpd -p x -k apache-httpd
-w /usr/sbin/nginx                         -p x -k nginx
-w /usr/local/nginx/sbin/nginx             -p x -k nginx
-w /usr/local/openresty/nginx/sbin/nginx   -p x -k nginx

For reliable process tracking that is required for assigning and propagating process labels, it is useful to have the Linux Audit subsystem produce events for all fork/exec style syscalls.

## Ignore clone( flags=CLONE_VM|... ), log other process-creating calls
-a never,exit  -F arch=b32 -S clone -F a2&0x100
-a never,exit  -F arch=b64 -S clone -F a2&0x100
-a always,exit -F arch=b32 -S fork,vfork,clone,clone3 -k fork
-a always,exit -F arch=b64 -S fork,vfork,clone,clone3 -k fork
-a always,exit -F arch=b32 -S execve,execveat
-a always,exit -F arch=b64 -S execve,execveat

It is only important that Laurel gets to observe these events. To reduce log volume, Laurel’s filtering settings should be used, e.g.:

[filter]
filter-keys = ["fork"]
filter-action = drop
keep-first-per-process = true

We are interested in ptrce usage, but not in every transaction (PEEK, POKE, CONT)

-a never,exit -F arch=b32 -S ptrace -F a0>=1 -F a0<=7
-a never,exit -F arch=b64 -S ptrace -F a0>=1 -F a0<=7
-a always,exit -F arch=b32 -S ptrace
-a always,exit -F arch=b64 -S ptrace

Usage of BPF should be restricted to few processes; log everything except data transfer operations because they would put too much load on the system.

-a never,exit -F arch=b32 -S bpf -F a0>=1 -F a0<=4
-a never,exit -F arch=b64 -S bpf -F a0>=1 -F a0<=4
-a never,exit -F arch=b32 -S bpf -F a0>=0xb -F a0<=0xf
-a never,exit -F arch=b64 -S bpf -F a0>=0xb -F a0<=0xf
-a never,exit -F arch=b32 -S bpf -F a0=0x13
-a never,exit -F arch=b64 -S bpf -F a0=0x13
-a always,exit -F arch=b32 -S bpf -F success=1
-a always,exit -F arch=b64 -S bpf -F success=1
    

-a always,exit -F arch=b32 -S init_module,finit_module,delete_module -k module
-a always,exit -F arch=b64 -S init_module,finit_module,delete_module -k module

audit.rules(7), laurel(8)

•
Hilko Bengen <bengen@hilluzination.de>
laurel 0.6.4
QR Code