[TUHS] Happy birthday, Morris Worm!

[don@DonHopkins.com (Don Hopkins)]

From ulowell!page Mon Nov  7 17:59:18 1988
Subject: worm report
Status: RO

[I wrote this for our local users; thought you might like a copy  ..Bob]





                     A REPORT ON THE INTERNET WORM


                               Bob Page
                          University of Lowell
                      Computer Science Department


                            November 7, 1988


     [Because of the many misquotes the media have been giving,
     this report is Copyright (c) Bob Page, all rights reserved.
     Permission is granted to republish this ONLY if you republish
     it in its entirety.]


Here's the scoop on the "Internet Worm".  Actually it's not a virus -
a virus is a piece of code that adds itself to other programs,
including operating systems.  It cannot run independently, but rather
requires that its "host" program be run to activate it.  As such, it
has a clear analog to biologic viruses -- those viruses are not
considered live, but they invade host cells and take them over, making
them produce new viruses.

A worm is a program that can run by itself and can propagate a fully
working version of itself to other machines.  As such, what was loosed
on the Internet was clearly a worm.

This data was collected through an emergency mailing list set up by
Gene Spafford at Purdue University, for administrators of major
Internet sites - some of the text is included verbatim from that list.
Mail was heavy since the formation of the list; it continues to be on
Monday afternoon - I get at least 2-3 messages every hour.  It's
possible that some of this information is incomplete, but I thought
you'd like to know what I know so far.

The basic object of the worm is to get a shell on another machine so
it can reproduce further.  There are three ways it attacks: sendmail,
fingerd, and rsh/rexec.


THE SENDMAIL ATTACK:

In the sendmail attack, the worm opens a TCP connection to another
machine's sendmail (the SMTP port), invokes debug mode, and sends a
RCPT TO that requests its data be piped through a shell.  That data, a
shell script (first-stage bootstrap) creates a temporary second-stage
bootstrap file called x$$,l1.c (where '$$' is the current process ID).
This is a small (40-line) C program.

The first-stage bootstrap compiles this program with the local cc and
executes it with arguments giving the Internet hostid/socket/password
of where it just came from.  The second-stage bootstrap (the compiled
C program) sucks over two object files, x$$,vax.o and x$$,sun3.o from
the attacking host.  It has an array for 20 file names (presumably for
20 different machines), but only two (vax and sun) were compiled in to
this code.  It then figures out whether it's running under BSD or
SunOS and links the appropriate file against the C library to produce
an executable program called /usr/tmp/sh - so it looks like the Bourne
shell to anyone who looked there.


THE FINGERD ATTACK:

In the fingerd attack, it tries to infiltrate systems via a bug in
fingerd, the finger daemon.  Apparently this is where most of its
success was (not in sendmail, as was originally reported).  When
fingerd is connected to, it reads its arguments from a pipe, but
doesn't limit how much it reads.  If it reads more than the internal
512-byte buffer allowed, it writes past the end of its stack.  After
the stack is a command to be executed ("/usr/ucb/finger") that
actually does the work.  On a VAX, the worm knew how much further from
the stack it had to clobber to get to this command, which it replaced
with the command "/bin/sh" (the bourne shell).  So instead of the
finger command being executed, a shell was started with no arguments.
Since this is run in the context of the finger daemon, stdin and
stdout are connected to the network socket, and all the files were
sucked over just like the shell that sendmail provided.


THE RSH/REXEC ATTACK:

The third way it tried to get into systems was via the .rhosts and
/etc/hosts.equiv files to determine 'trusted' hosts where it might be
able to migrate to.  To use the .rhosts feature, it needed to actually
get into people's accounts - since the worm was not running as root
(it was running as daemon) it had to figure out people's passwords.
To do this, it went through the /etc/passwd file, trying to guess
passwords.  It tried combinations of: the username, the last, first,
last+first, nick names (from the GECOS field), and a list of special
"popular" passwords:

aaa       cornelius     guntis    noxious   simon
academia      couscous      hacker    nutrition simple
aerobics      creation      hamlet    nyquist   singer
airplane      creosote      handily   oceanography  single
albany        cretin        happening     ocelot    smile
albatross     daemon        harmony   olivetti  smiles
albert        dancer        harold    olivia    smooch
alex          daniel        harvey    oracle    smother
alexander     danny     hebrides      orca      snatch
algebra       dave      heinlein      orwell    snoopy
aliases       december      hello     osiris    soap
alphabet      defoe     help      outlaw    socrates
ama       deluge        herbert   oxford    sossina
amorphous     desperate     hiawatha      pacific   sparrows
analog        develop       hibernia      painless  spit
anchor        dieter        honey     pakistan  spring
andromache    digital       horse     pam       springer
animals       discovery     horus     papers    squires
answer        disney        hutchins      password  strangle
anthropogenic dog       imbroglio     patricia  stratford
anvils        drought       imperial      penguin   stuttgart
anything      duncan        include   peoria    subway
aria          eager     ingres    percolate success
ariadne       easier        inna      persimmon summer
arrow         edges     innocuous     persona   super
arthur        edinburgh     irishman      pete      superstage
athena        edwin     isis      peter     support
atmosphere    edwina        japan     philip    supported
aztecs        egghead       jessica   phoenix   surfer
azure         eiderdown     jester    pierre    suzanne
bacchus       eileen        jixian    pizza     swearer
bailey        einstein      johnny    plover    symmetry
banana        elephant      joseph    plymouth  tangerine
bananas       elizabeth     joshua    polynomial    tape
bandit        ellen     judith    pondering target
banks         emerald       juggle    pork      tarragon
barber        engine        julia     poster    taylor
baritone      engineer      kathleen      praise    telephone
bass          enterprise    kermit    precious  temptation
bassoon       enzyme        kernel    prelude   thailand
batman        ersatz        kirkland      prince    tiger
beater        establish     knight    princeton toggle
beauty        estate        ladle     protect   tomato
beethoven     euclid        lambda    protozoa  topography
beloved       evelyn        lamination    pumpkin   tortoise
benz          extension     larkin    puneet    toyota
beowulf       fairway       larry     puppet    trails
berkeley      felicia       lazarus   rabbit    trivial
berliner      fender        lebesgue      rachmaninoff  trombone
beryl         fermat        lee       rainbow   tubas
beverly       fidelity      leland    raindrop  tuttle
bicameral     finite        leroy     raleigh   umesh
bob       fishers       lewis     random    unhappy
brenda        flakes        light     rascal    unicorn
brian         float     lisa      really    unknown
bridget       flower        louis     rebecca   urchin
broadway      flowers       lynne     remote    utility
bumbling      foolproof     macintosh     rick      vasant
burgess       football      mack      ripple    vertigo
campanile     foresight     maggot    robotics  vicky
cantor        format        magic     rochester village
cardinal      forsythe      malcolm   rolex     virginia
carmen        fourier       mark      romano    warren
carolina      fred      markus    ronald    water
caroline      friend        marty     rosebud   weenie
cascades      frighten      marvin    rosemary  whatnot
castle        fun       master    roses     whiting
cat       fungible      maurice   ruben     whitney
cayuga        gabriel       mellon    rules     will
celtics       gardner       merlin    ruth      william
cerulean      garfield      mets      sal       williamsburg
change        gauss     michael   saxon     willie
charles       george        michelle      scamper   winston
charming      gertrude      mike      scheme    wisconsin
charon        ginger        minimum   scott     wizard
chester       glacier       minsky    scotty    wombat
cigar         gnu       moguls    secret    woodwind
classic       golfer        moose     sensor    wormwood
clusters      gorgeous      morley    serenity  yacov
coffee        gorges        mozart    sharks    yang
coke          gosling       nancy     sharon    yellowstone
collins       gouge     napoleon      sheffield yosemite
commrades     graham        nepenthe      sheldon   zap
computer      gryphon       ness      shiva     zimmerman
condo         guest     network   shivers
cookie        guitar        newton    shuttle
cooper        gumption      next      signature

[I wouldn't have picked some of these as "popular" passwords, but
then again, I'm not a worm writer.  What do I know?]

When everything else fails, it opens /usr/dict/words and tries every
word in the dictionary.  It is pretty successful in finding passwords,
as most people don't choose them very well.  Once it gets into
someone's account, it looks for a .rhosts file and does an 'rsh'
and/or 'rexec' to another host, it sucks over the necessary files into
/usr/tmp and runs /usr/tmp/sh to start all over again.


Between these three methods of attack (sendmail, fingerd, .rhosts)
it was able to spread very quickly.


THE WORM ITSELF:

The 'sh' program is the actual worm.  When it starts up it clobbers
its argv array so a 'ps' will not show its name.  It opens all its
necessary files, then unlinks (deletes) them so they can't be found
(since it has them open, however, it can still access the contents).
It then tries to infect as many other hosts as possible - when it
sucessfully connects to one host, it forks a child to continue the
infection while the parent keeps on trying new hosts.

One of the things it does before it attacks a host is connect to the
telnet port and immediately close it.  Thus, "telnetd: ttloop: peer
died" in /usr/adm/messages means the worm attempted an attack.

The worm's role in life is to reproduce - nothing more.  To do that it
needs to find other hosts.  It does a 'netstat -r -n' to find local
routes to other hosts & networks, looks in /etc/hosts, and uses the
yellow pages distributed hosts file if it's available.  Any time it
finds a host, it tries to infect it through one of the three methods,
see above.  Once it finds a local network (like 129.63.nn.nn for
ulowell) it sequentially tries every address in that range.

If the system crashes or is rebooted, most system boot procedures
clear /tmp and /usr/tmp as a matter of course, erasing any evidence.
However, sendmail log files show mail coming in from user /dev/null
for user /bin/sed, which is a tipoff that the worm entered.

Each time the worm is started, there is a 1/15 chance (it calls
random()) that it sends a single byte to ernie.berkeley.edu on some
magic port, apparently to act as some kind of monitoring mechanism.


THE CRACKDOWN:

Three main 'swat' teams from Berkeley, MIT and Purdue found copies of
the VAX code (the .o files had all the symbols intact with somewhat
meaningful names) and disassembled it into about 3000 lines of C.  The
BSD development team poked fun at the code, even going so far to point
out bugs in the code and supplying source patches for it!  They have
not released the actual source code, however, and refuse to do so.
That could change - there are a number of people who want to see the
code.

Portions of the code appear incomplete, as if the program development
was not yet finished.  For example, it knows the offset needed to
break the BSD fingerd, but doesn't know the correct offset for Sun's
fingerd (which causes it to dump core); it also doesn't erase its
tracks as cleverly as it might; and so on.
The worm uses a variable called 'pleasequit' but doesn't correctly
initialize it, so some folks added a module called _worm.o to the C
library, which is produced from:
        int pleasequit = -1;
the fact that this value is set to -1 will cause it to exit after one
iteration.

The close scrutiny of the code also turned up comments on the
programmer's style.  Verbatim from someone at MIT:
    From disassembling the code, it looks like the programmer
    is really anally retentive about checking return codes,
    and, in addition, prefers to use array indexing instead of
    pointers to walk through arrays.

Anyone who looks at the binary will not see any embedded strings -
they are XOR'ed with 81 (hex).  That's how the shell commands are
imbedded.  The "obvious" passwords are stored with their high bit set.

Although it spreads very fast, it is somewhat slowed down by the fact
that it drives the load average up on the machine - this is due to all
the encryptions going on, and the large number of incoming worms from
other machines.

[Initially, the fastest defense against the worm is is to create a
directory called /usr/tmp/sh.  The script that creates /usr/tmp/sh
from one of the .o files checks to see if /usr/tmp/sh exists, but not
to see if it's a directory.  This fix is known as 'the condom'.]


NOW WHAT?

None of the ULowell machines were hit by the worm.  When BBN staffers
found their systems infected, they cut themselves off from all other
hosts.  Since our connection to the Internet is through BBN, we were
cut off as well.  Before we were cut off, I received mail about the
sendmail problem and installed a patch to disable the feature the worm
uses to get in through sendmail.  I had made local modifications to
fingerd which changed the offsets, so any attempt to scribble over the
stack would probably have ended up in a core dump.

Most Internet systems running 4.3BSD or SunOS have installed the
necessary patches to close the holes and have rejoined the Internet.
As you would expect, there is a renewed interest in system/network
security, finding and plugging holes, and speculation over what
will happen to the worm's creator.

If you haven't read or watched the news, various log files have named
the responsible person as Robert Morris Jr., a 23-year old doctoral
student at Cornell.  His father is head of the National Computer
Security Center, the NSA's public effort in computer security, and has
lectured widely on security aspects of UNIX.

Associates of the student claim the worm was a 'mistake' - that he
intended to unleash it but it was not supposed to move so quickly or
spread so much.  His goal (from what I understand) was to have a
program 'live' within the Internet.  If the reports that he intended
it to spread slowly are true, then it's possible that the bytes sent
to ernie.berkeley.edu were intended to monitor the spread of the
worm.  Some news reports mentioned that he panicked when, via some
"monitoring mechanism" he saw how fast it had propagated.

A source inside DEC reports that although the worm didn't make much
progress there, it was sighted on several machines that wouldn't be
on its normal propagation path, i.e. not gateways and not on the same
subnet.  These machines are not reachable from the outside.  Morris
was a summer intern at DEC in '87.  He might have included names or
addresses he remembered as targets for infesting hidden internal
networks.  Most of the DEC machines in question belong to the group he
worked in.

The final word has not been written - I don't think the FBI have even
met with this guy yet.  It will be interesting to see what happens.


 barry r. butterklee
 aoi systems, inc.
 650 suffolk street
 lowell, ma 01854
 (508)937-5400

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