rule ACBackdoor_ELF: linux malware backdoor
{
    meta:
        author = "Adam M. Swanda"
        date = "Nov 2019"
        reference = "https://www.intezer.com/blog-acbackdoor-analysis-of-a-new-multiplatform-backdoor/"

    strings:
        $ua_str = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 1.1.4322)" ascii fullword
        $header1 = "Access-Control:" ascii fullword
        $header2 = "X-Access" ascii

        $initd = "/etc/init.d/update-notifier" ascii fullword
        $str001 = "#!/bin/sh -e" ascii fullword
        $str002 = "### BEGIN INIT INFO" ascii fullword
        $str003 = "# Provides:          update-notifier" ascii fullword
        $str004 = "# Required-Start:    $local_fs" ascii fullword
        $str005 = "# Required-Stop:" ascii fullword
        $str006 = "# Default-Start:     S" ascii fullword
        $str007 = "# Default-Stop:" ascii fullword
        $str008 = "### END INIT INFO" ascii fullword
        $str010 = "  *) echo \"Usage: $0 {start|stop|restart|force-reload}\" >&2; ;;" ascii fullword
        $str011 = "esac" ascii fullword
        $str012 = "[ -x /usr/local/bin/update-notifier ] \\" ascii fullword
        $str013 = "    && exec /usr/local/bin/update-notifier" ascii fullword
        $rcd01 = "/etc/rc2.d/S01update-notifier" ascii fullword
        $rcd02 = "/etc/rc3.d/S01update-notifier" ascii fullword
        $rcd03 = "/etc/rc5.d/S01update-notifier" ascii fullword

    condition:
        /* trigger = '{7f 45 4c 46}' - ELF magic bytes */
        (uint32be(0x0) == 0x7f454c46)
        and
        (
            ($ua_str and all of ($header*) and $initd and all of ($rcd*))
            or
            (
                $ua_str and all of ($header*) and 10 of ($str*)
            )
        )
}