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		THE COMPUTER INCIDENT ADVISORY CAPABILITY

 				CIAC

			ADVISORY    NOTICE
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			Security Holes in UNIX Systems

   The DOE Computer Incident Advisory Capability (CIAC) at LLNL has learned 
   that there are two security holes which leave certain systems running the 
   UNIX Operating System vulnerable to intrusion.  The holes, when used together
   in a very specific scenario, permit an intruder to attack UNIX systems 
   over the Internet and other pathways, and to assume superuser privileges.  
   Therefore, these vulnerabilities constitute a highly severe threat.  Sun
   systems running SunOS 3.x and 4.0 are susceptible; the hole may exist in
   other versions of the UNIX operating system as well.  A brief description 
   of the holes follow: 

	1.  There is a long-known hole in tftp, the user interface to the 
	    Internet TFTP (Trivial File Transfer Protocol).  This hole allows 
	    any user, without first logging in, to read any readable file and 
	    to write any writable file on a remote system via Internet.  This
	    hole exists in SunOS 3.x, but has been fixed in SunOS 4.0.

	    To determine whether this hole affects a system, do the following:

	    	Enter tftp local_testing_system at the UNIX prompt and follow
		with a carriage return.  For example,

			% tftp styx <RET>

		The system should answer with the tftp prompt:

			tftp>

		Enter the following at the prompt:

			tftp>  get /etc/passwd stolen_pw

 	    If "Error code 1: File not found" appears, the tested system is
	    safe from remote attacks.  However, it may still be susceptible to 
	    local attacks.

	2.  There are holes in rwalld (the network rwall server daemon) and 
	    wall (write to all users).  The command "wall" writes to filenames
            encoded within /etc/utmp.  You are vulnerable to this hole if
            /etc/utmp is world and/or group writable.  In essence, an intruder
            can use this hole to write on any file on the computer system. 

   Any UNIX machine which runs a windowing system is likely to have the 
   privileges which create the described vulnerabilities.  The presence of 
   an intruder who exploits these holes is difficult to detect.  It is our
   understanding that knowledge of these holes has been distributed widely 
   within the hacker community.  It is advisable, based on your vulnerability,
   to take appropriate action for your site.

   CIAC is currently working with Sun Microsystems and DARPA's Computer 
   Emergency Response Team (CERT) to eliminate these vulnerabilities as
   quickly as possible.  You will be notified when a patch is available.  For
   further information, contact CIAC at (415) 422-8193 or (FTS) 532-8193, or
   send e-mail to gschultz%nsspa@icdc.llnl.gov.