process where host.os.type == "linux" and event.type == "start" and event.action == "exec" and
process.name == "ln" and process.args in ("-s", "-sf") and
  (
    /* suspicious files */
    (process.args in ("/etc/shadow", "/etc/shadow-", "/etc/shadow~", "/etc/gshadow", "/etc/gshadow-") or
    (process.working_directory == "/etc" and process.args in ("shadow", "shadow-", "shadow~", "gshadow", "gshadow-"))) or

    /* suspicious bins */
    (process.args in ("/bin/bash", "/bin/dash", "/bin/sh", "/bin/tcsh", "/bin/csh", "/bin/zsh", "/bin/ksh", "/bin/fish") or
    (process.working_directory == "/bin" and process.args : ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish"))) or
    (process.args in ("/usr/bin/bash", "/usr/bin/dash", "/usr/bin/sh", "/usr/bin/tcsh", "/usr/bin/csh", "/usr/bin/zsh", "/usr/bin/ksh", "/usr/bin/fish") or
    (process.working_directory == "/usr/bin" and process.args in ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish"))) or

    /* suspicious locations */
    (process.args : ("/etc/cron.d/*", "/etc/cron.daily/*", "/etc/cron.hourly/*", "/etc/cron.weekly/*", "/etc/cron.monthly/*")) or
    (process.args : ("/home/*/.ssh/*", "/root/.ssh/*","/etc/sudoers.d/*", "/dev/shm/*"))
  ) and
  process.parent.name in ("bash", "dash", "ash", "sh", "tcsh", "csh", "zsh", "ksh", "fish") and
  not user.Ext.real.id == "0" and not group.Ext.real.id == "0"