Questions: LKM, yoyo & rootkits

From: Gordon Ewasiuk (gewasiukat_private)
Date: Fri Feb 21 2003 - 05:31:43 PST

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    Just caught a variant of yoyo, a linux rookit based on lrk.
    
    http://security.alldas.mirror.widexs.nl/analysis/?aid=2
    
    Has anyone dealt with yoyo?  The system in question will be getting a
    fresh install of Redhat but I'm curious about some of the symptoms seen.
    
    1)  The backdoor was loaded from /usr/lib/setup via /etc/rc.d/rc.local
    *AND* /etc/rc.d/rc.sysinit.  Both files were cleaned and the backdoor
    removed.  Upon reboot, rc.local and rc.sysinit were modified again - this
    time they were chattr'ed.
    
    2)  Does this rootkit affect rpm databases?  Rpm was serious broke after
    the rootkit.
    
    3)  When all visable signs of the rootkit were removed, rpms were
    refreshed from r/o media, and the system was rebooted, an interesting
    behavior was observed:
    	logging in as root
    	lsof | grep 3409 show nothing
    	netstat -apm | grep 3409
    	nothing would be displayed
    	a minute later, netstat would show up with a PID in 800-820 range
    and would appear to be bound to udp/3409.  probes to 3409/udp from an
    external machine would fail.  the port appears bound but doesn't respond
    to network requests
    	this behavior would continue with any other processes started by
    root
    
    4)  Is yoyo an LKM?
    
    Finally, have any php exploits been associated with yoyo?  While
    researching yoyo, I found some hidden directories with phpscan and some
    other php-named utilities.
    
    The system is getting a fresh installation shortly, but curiousity has
    gotten to me.
    
    Regards,
    
    -gordon
    
    
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