LoFP LoFP / trusted system module updates or allowed pluggable authentication module (pam) daemon configuration changes.

Techniques

Sample rules

Pluggable Authentication Module (PAM) Source Download

Description

This rule detects the usage of curl or wget to download the source code of a Pluggable Authentication Module (PAM) shared object file. Attackers may download the source code of a PAM shared object file to create a backdoor in the authentication process.

Detection logic

process where host.os.type == "linux" and event.type == "start" and event.action in ("exec", "exec_event") and
process.name in ("curl", "wget") and
process.args like~ "https://github.com/linux-pam/linux-pam/releases/download/v*/Linux-PAM-*.tar.xz"

Potential Backdoor Execution Through PAM_EXEC

Description

This rule detects SSH session ID change followed by a suspicious SSHD child process, this may indicate the successful execution of a potentially malicious process through the Pluggable Authentication Module (PAM) utility. PAM is a framework used by Linux systems to authenticate users. Adversaries may create malicious PAM modules that grant them persistence onto the target every time a user logs in by executing a backdoor script or command.

Detection logic

sequence by process.entity_id with maxspan=3s
  [process where host.os.type == "linux" and event.type == "change" and event.action == "session_id_change" and process.name in ("ssh", "sshd")]
  [process where host.os.type == "linux" and event.type == "start" and event.action == "exec" and process.parent.name in ("ssh", "sshd") and
   process.args_count == 2 and (
     process.name like ("perl*", "python*", "php*", "ruby*", "lua*") or
     process.executable like (
       "/tmp/*", "/var/tmp/*", "/dev/shm/*", "./*", "/boot/*", "/sys/*", "/lost+found/*", "/media/*", "/proc/*",
       "/var/backups/*", "/var/log/*", "/var/mail/*", "/var/spool/*") or
     process.name like ".*"
   )]

Pluggable Authentication Module (PAM) Creation in Unusual Directory

Description

This rule detects the creation of Pluggable Authentication Module (PAM) shared object files in unusual directories. Attackers may compile PAM shared object files in temporary directories, to move them to system directories later, potentially allowing them to maintain persistence on a compromised system, or harvest account credentials.

Detection logic

file where host.os.type == "linux" and event.type == "creation" and file.name like "pam_*.so" and not file.path like (
  "/lib/security/*",
  "/lib64/security/*",
  "/lib/x86_64-linux-gnu/security/*",
  "/usr/lib/security/*",
  "/usr/lib64/security/*",
  "/usr/lib/x86_64-linux-gnu/security/*"
) and not (
  process.name in ("dockerd", "containerd", "steam", "buildkitd", "unsquashfs", "pacman") or
  file.path like (
    "/build/rootImage/nix/store/*", "/home/*/.local/share/containers/*", "/nix/store/*", "/var/lib/containerd/*",
    "/var/snap/*", "/usr/share/nix/nix/store/*", "/tmp/cura/squashfs-root/*", "/home/*/docker/*", "/tmp/containerd*"
  )
)

Creation or Modification of Pluggable Authentication Module or Configuration

Description

This rule monitors for the creation or modification of Pluggable Authentication Module (PAM) shared object files or configuration files. Attackers may create or modify these files to maintain persistence on a compromised system, or harvest account credentials.

Detection logic

file where host.os.type == "linux" and event.action in ("rename", "creation") and
process.executable != null and (
  (file.path like~ (
    "/lib/security/*", "/lib64/security/*", "/usr/lib/security/*", "/usr/lib64/security/*",
    "/lib/x86_64-linux-gnu/security/*", "/usr/lib/x86_64-linux-gnu/security/*"
  ) and file.extension == "so") or
  (file.path like~ "/etc/pam.d/*" and file.extension == null) or
  (file.path like~ "/etc/security/pam_*" or file.path == "/etc/pam.conf")
) and not (
  process.executable in (
    "/bin/dpkg", "/usr/bin/dpkg", "/bin/dockerd", "/usr/bin/dockerd", "/usr/sbin/dockerd", "/bin/microdnf",
    "/usr/bin/microdnf", "/bin/rpm", "/usr/bin/rpm", "/bin/snapd", "/usr/bin/snapd", "/bin/yum", "/usr/bin/yum",
    "/bin/dnf", "/usr/bin/dnf", "/bin/podman", "/usr/bin/podman", "/bin/dnf-automatic", "/usr/bin/dnf-automatic",
    "/bin/pacman", "/usr/bin/pacman", "/usr/bin/dpkg-divert", "/bin/dpkg-divert", "/sbin/apk", "/usr/sbin/apk",
    "/usr/local/sbin/apk", "/usr/bin/apt", "/usr/sbin/pacman", "/bin/podman", "/usr/bin/podman", "/usr/bin/puppet",
    "/bin/puppet", "/opt/puppetlabs/puppet/bin/puppet", "/usr/bin/chef-client", "/bin/chef-client",
    "/bin/autossl_check", "/usr/bin/autossl_check", "/proc/self/exe", "/dev/fd/*",  "/usr/bin/pamac-daemon",
    "/bin/pamac-daemon", "/usr/lib/snapd/snapd", "/usr/local/bin/dockerd", "/usr/sbin/pam-auth-update",
    "/usr/lib/systemd/systemd", "/usr/libexec/packagekitd", "/usr/bin/bsdtar", "/sbin/pam-auth-update"
  ) or
  file.path like (
    "/tmp/snap.rootfs_*/pam_*.so", "/tmp/newroot/lib/*/pam_*.so", "/tmp/newroot/usr/lib64/security/pam_*.so"
  ) or
  file.extension in ("swp", "swpx", "swx", "dpkg-remove") or
  file.Ext.original.extension == "dpkg-new" or
  process.executable like (
    "/nix/store/*", "/var/lib/dpkg/*", "/snap/*", "/dev/fd/*", "/usr/lib/virtualbox/*"
  ) or
  (process.name == "sed" and file.name like~ "sed*") or
  (process.name == "perl" and file.name like~ "e2scrub_all.tmp*")
)

Modification of Standard Authentication Module or Configuration

Description

Adversaries may modify the standard authentication module for persistence via patching the normal authorization process or modifying the login configuration to allow unauthorized access or elevate privileges.

Detection logic

event.category:file and event.type:change and
  (file.name:pam_*.so or file.path:(/etc/pam.d/* or /private/etc/pam.d/* or /usr/lib64/security/*)) and
  process.executable:
    (* and
      not
      (
        /usr/libexec/packagekitd or
        /usr/bin/vim or
        /usr/libexec/xpcproxy or
        /usr/bin/bsdtar or
        /usr/local/bin/brew or
        "/System/Library/PrivateFrameworks/PackageKit.framework/Versions/A/XPCServices/package_script_service.xpc/Contents/MacOS/package_script_service"
      )
    ) and
  not file.path:
         (
           /tmp/snap.rootfs_*/pam_*.so or
           /tmp/newroot/lib/*/pam_*.so or
           /private/var/folders/*/T/com.apple.fileprovider.ArchiveService/TemporaryItems/*/lib/security/pam_*.so or
           /tmp/newroot/usr/lib64/security/pam_*.so
         ) and
  not process.name:
         (
           yum or dnf or rsync or platform-python or authconfig or rpm or pdkg or apk or dnf-automatic or btrfs or
           dpkg or pam-auth-update or steam or platform-python3.6 or pam-config or microdnf or yum_install or yum-cron or
           systemd or containerd or pacman
         )