292 lines
16 KiB
Plaintext
292 lines
16 KiB
Plaintext
==Phrack Inc.==
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Volume Two, Issue 22, File 8 of 12
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"]}`"`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\
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\`\`\ \`\`\
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\`\ A Report On The InterNet Worm \`\
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\`\ \`\
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\`\ By Bob Page \`\
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\`\ \`\
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\`\ University of Lowell \`\
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\`\ Computer Science Department \`\
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\`\ \`\
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\`\ November 7, 1988 \`\
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\`\`\ \`\`\
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\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\`\
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Here's the truth about the "Internet Worm." Actually it's not a virus -
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a virus is a piece of code that adds itself to other programs, including
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operating systems. It cannot run independently, but rather requires that its
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"host" program be run to activate it. As such, it has a clear analog to
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biologic viruses -- those viruses are not considered live, but they invade host
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cells and take them over, making them produce new viruses.
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A worm is a program that can run by itself and can propagate a fully working
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version of itself to other machines. As such, what was loosed on the Internet
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was clearly a worm.
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This data was collected through an emergency mailing list set up by Gene
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Spafford at Purdue University, for administrators of major Internet sites -
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some of the text is included verbatim from that list.
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The basic object of the worm is to get a shell on another machine so it can
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reproduce further. There are three ways it attacks: sendmail, fingerd, and
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rsh/rexec.
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- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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The Sendmail Attack:
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In the sendmail attack, the worm opens a TCP connection to another machine's
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sendmail (the SMTP port), invokes debug mode, and sends a RCPT TO that requests
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its data be piped through a shell. That data, a shell script (first-stage
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bootstrap) creates a temporary second-stage bootstrap file called x$$,l1.c
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(where '$$' is the current process ID). This is a small (40-line) C program.
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The first-stage bootstrap compiles this program with the local cc and executes
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it with arguments giving the Internet hostid/socket/password of where it just
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came from. The second-stage bootstrap (the compiled C program) sucks over two
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object files, x$$,vax.o and x$$,sun3.o from the attacking host. It has an
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array for 20 file names (presumably for 20 different machines), but only two
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(vax and sun) were compiled in to this code. It then figures out whether it's
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running under BSD or SunOS and links the appropriate file against the C library
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to produce an executable program called /usr/tmp/sh - so it looks like the
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Bourne shell to anyone who looked there.
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The Fingerd Attack:
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In the fingerd attack, it tries to infiltrate systems via a bug in fingerd, the
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finger daemon. Apparently this is where most of its success was (not in
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sendmail, as was originally reported). When fingerd is connected to, it reads
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its arguments from a pipe, but doesn't limit how much it reads. If it reads
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more than the internal 512-byte buffer allowed, it writes past the end of its
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stack. After the stack is a command to be executed ("/usr/ucb/finger") that
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actually does the work. On a VAX, the worm knew how much further from the
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stack it had to clobber to get to this command, which it replaced with the
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command "/bin/sh" (the bourne shell). So instead of the finger command being
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executed, a shell was started with no arguments. Since this is run in the
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context of the finger daemon, stdin and stdout are connected to the network
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socket, and all the files were sucked over just like the shell that sendmail
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provided.
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The Rsh/Rexec Attack:
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The third way it tried to get into systems was via the .rhosts and
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/etc/hosts.equiv files to determine 'trusted' hosts where it might be able to
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migrate to. To use the .rhosts feature, it needed to actually get into
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people's accounts - since the worm was not running as root (it was running as
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daemon) it had to figure out people's passwords. To do this, it went through
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the /etc/passwd file, trying to guess passwords. It tried combinations of: the
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username, the last, first, last+first, nick names (from the GECOS field), and a
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list of special "popular" passwords:
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aaa cornelius guntis noxious simon
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academia couscous hacker nutrition simple
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aerobics creation hamlet nyquist singer
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airplane creosote handily oceanography single
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albany cretin happening ocelot smile
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albatross daemon harmony olivetti smiles
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albert dancer harold olivia smooch
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alex daniel harvey oracle smother
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alexander danny hebrides orca snatch
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algebra dave heinlein orwell snoopy
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aliases december hello osiris soap
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alphabet defoe help outlaw socrates
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ama deluge herbert oxford sossina
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amorphous desperate hiawatha pacific sparrows
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analog develop hibernia painless spit
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anchor dieter honey pakistan spring
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andromache digital horse pam springer
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animals discovery horus papers squires
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answer disney hutchins password strangle
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anthropogenic dog imbroglio patricia stratford
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anvils drought imperial penguin stuttgart
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anything duncan include peoria subway
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aria eager ingres percolate success
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ariadne easier inna persimmon summer
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arrow edges innocuous persona super
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arthur edinburgh irishman pete superstage
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athena edwin isis peter support
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atmosphere edwina japan philip supported
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aztecs egghead jessica phoenix surfer
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azure eiderdown jester pierre suzanne
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bacchus eileen jixian pizza swearer
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bailey einstein johnny plover symmetry
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banana elephant joseph plymouth tangerine
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bananas elizabeth joshua polynomial tape
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bandit ellen judith pondering target
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banks emerald juggle pork tarragon
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barber engine julia poster taylor
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baritone engineer kathleen praise telephone
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bass enterprise kermit precious temptation
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bassoon enzyme kernel prelude thailand
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batman ersatz kirkland prince tiger
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beater establish knight princeton toggle
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beauty estate ladle protect tomato
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beethoven euclid lambda protozoa topography
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beloved evelyn lamination pumpkin tortoise
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benz extension larkin puneet toyota
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beowulf fairway larry puppet trails
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berkeley felicia lazarus rabbit trivial
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berliner fender lebesgue rachmaninoff trombone
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beryl fermat lee rainbow tubas
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beverly fidelity leland raindrop tuttle
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bicameral finite leroy raleigh umesh
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bob fishers lewis random unhappy
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brenda flakes light rascal unicorn
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brian float lisa really unknown
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bridget flower louis rebecca urchin
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broadway flowers lynne remote utility
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bumbling foolproof macintosh rick vasant
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burgess football mack ripple vertigo
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campanile foresight maggot robotics vicky
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cantor format magic rochester village
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cardinal forsythe malcolm rolex virginia
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carmen fourier mark romano warren
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carolina fred markus ronald water
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caroline friend marty rosebud weenie
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cascades frighten marvin rosemary whatnot
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castle fun master roses whiting
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cat fungible maurice ruben whitney
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cayuga gabriel mellon rules will
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celtics gardner merlin ruth william
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cerulean garfield mets sal williamsburg
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change gauss michael saxon willie
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charles george michelle scamper winston
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charming gertrude mike scheme wisconsin
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charon ginger minimum scott wizard
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chester glacier minsky scotty wombat
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cigar gnu moguls secret woodwind
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classic golfer moose sensor wormwood
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clusters gorgeous morley serenity yaco
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coffee gorges mozart sharks yang
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coke gosling nancy sharon yellowstone
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collins gouge napoleon sheffield yosemite
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commrades graham nepenthe sheldon zap
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computer gryphon ness shiva zimmerman
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condo guest network shivers
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cookie guitar newton shuttle
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cooper gumption next signature
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When everything else fails, it opens /usr/dict/words and tries every word in
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the dictionary. It is pretty successful in finding passwords, as most people
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don't choose them very well. Once it gets into someone's account, it looks for
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a .rhosts file and does an 'rsh' and/or 'rexec' to another host, it sucks over
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the necessary files into /usr/tmp and runs /usr/tmp/sh to start all over again.
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Between these three methods of attack (sendmail, fingerd, .rhosts) it was able
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to spread very quickly.
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The Worm Itself:
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The 'sh' program is the actual worm. When it starts up it clobbers its argv
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array so a 'ps' will not show its name. It opens all its necessary files, then
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unlinks (deletes) them so they can't be found (since it has them open, however,
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it can still access the contents). It then tries to infect as many other hosts
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as possible - when it sucessfully connects to one host, it forks a child to
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continue the infection while the parent keeps on trying new hosts.
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One of the things it does before it attacks a host is connect to the telnet
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port and immediately close it. Thus, "telnetd: ttloop: peer died" in
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/usr/adm/messages means the worm attempted an attack.
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The worm's role in life is to reproduce - nothing more. To do that it needs to
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find other hosts. It does a 'netstat -r -n' to find local routes to other
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hosts & networks, looks in /etc/hosts, and uses the yellow pages distributed
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hosts file if it's available. Any time it finds a host, it tries to infect it
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through one of the three methods, see above. Once it finds a local network
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(like 129.63.nn.nn for ulowell) it sequentially tries every address in that
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range.
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If the system crashes or is rebooted, most system boot procedures clear /tmp
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and /usr/tmp as a matter of course, erasing any evidence. However, sendmail
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log files show mail coming in from user /dev/null for user /bin/sed, which is a
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tipoff that the worm entered.
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Each time the worm is started, there is a 1/15 chance (it calls random()) that
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it sends a single byte to ernie.berkeley.edu on some magic port, apparently to
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act as some kind of monitoring mechanism.
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The Crackdown:
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Three main 'swat' teams from Berkeley, MIT and Purdue found copies of the VAX
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code (the .o files had all the symbols intact with somewhat meaningful names)
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and disassembled it into about 3000 lines of C. The BSD development team poked
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fun at the code, even going so far to point out bugs in the code and supplying
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source patches for it! They have not released the actual source code, however,
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and refuse to do so. That could change - there are a number of people who want
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to see the code.
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Portions of the code appear incomplete, as if the program development was not
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yet finished. For example, it knows the offset needed to break the BSD
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fingerd, but doesn't know the correct offset for Sun's fingerd (which causes it
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to dump core); it also doesn't erase its tracks as cleverly as it might; and so
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on.
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The worm uses a variable called 'pleasequit' but doesn't correctly initialize
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it, so some folks added a module called _worm.o to the C library, which is
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produced from: int pleasequit = -1; the fact that this value is set to -1 will
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cause it to exit after one iteration.
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The close scrutiny of the code also turned up comments on the programmer's
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style. Verbatim from someone at MIT:
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From disassembling the code, it looks like the programmer is really
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anally retentive about checking return codes, and, in addition,
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prefers to use array indexing instead of pointers to walk through
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arrays.
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Anyone who looks at the binary will not see any embedded strings - they are
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XOR'ed with 81 (hex). That's how the shell commands are imbedded. The
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"obvious" passwords are stored with their high bit set.
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Although it spreads very fast, it is somewhat slowed down by the fact that it
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drives the load average up on the machine - this is due to all the encryptions
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going on, and the large number of incoming worms from other machines.
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[Initially, the fastest defense against the worm is is to create a directory
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called /usr/tmp/sh. The script that creates /usr/tmp/sh from one of the .o
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files checks to see if /usr/tmp/sh exists, but not to see if it's a directory.
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This fix is known as 'the condom'.]
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Now What?
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Most Internet systems running 4.3BSD or SunOS have installed the necessary
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patches to close the holes and have rejoined the Internet. As you would
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expect, there is a renewed interest in system/network security, finding and
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plugging holes, and speculation over what will happen to the worm's creator.
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If you haven't read or watched the news, various log files have named
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the responsible person as Robert Morris Jr., a 23-year old doctoral student at
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Cornell. His father is head of the National Computer Security Center, the
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NSA's public effort in computer security, and has lectured widely on security
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aspects of UNIX.
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Associates of the student claim the worm was a 'mistake' - that he intended to
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unleash it but it was not supposed to move so quickly or spread so much. His
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goal was to have a program 'live' within the Internet. If the reports that he
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intended it to spread slowly are true, then it's possible that the bytes sent
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to ernie.berkeley.edu were intended to monitor the spread of the worm. Some
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news reports mentioned that he panicked when, via some "monitoring mechanism"
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he saw how fast it had propagated.
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A source inside DEC reports that although the worm didn't make much progress
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there, it was sighted on several machines that wouldn't be on its normal
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propagation path, i.e. not gateways and not on the same subnet. These machines
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are not reachable from the outside. Morris was a summer intern at DEC in '87.
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He might have included names or addresses he remembered as targets for
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infesting hidden internal networks. Most of the DEC machines in question
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belong to the group he worked in.
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The final word has not been written...
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...it will be interesting to see what happens.
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_______________________________________________________________________________
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