helper program has an array of 20 filenames for the "helper" to
copy over, so there is room to spare. There are two versions
copied -- a version for Vax BSD and a version for SunOS; the
appropriate one is compiled.
6) The new virus is dispatched. This virus opens all the virus
source files, then unlinks the files so they can't be found (since
it has them open, however, it can still access the contents).
Next, the virus steps through the hosts file (on the Sun, it uses
YP to step through the distributed hosts file) trying to connect
to other machines' sendmail. If a connection succeeds, it forks a
child process to infect it, while the parent continues to attempt
infection of other machines.
7) The child requests and initializes a new socket, then builds
and invokes a listener with the new socket number and hostid as
arguments (#1, above).
The heavy load we see is the result of multiple viruses coming in
from multiple sites. Since local hosts files tend to have entries
for other local hosts, the virus tends to infect local machines
multiple times -- in some senses this is lucky since it helps
prevent the spread of the virus as the local machines slow down.
The virus also "cleans" up after itself. If you reboot an
infected machine (or it crashes), the /tmp directory is normally
cleaned up on reboot. The other incriminating files were already
deleted by the virus itself.
Clever, nasty, and definitely anti-social.
--spaf
------------------------------------------------------------------
-------
From: bishop@bear.Dartmouth.EDU (Matt Bishop)
Subject: More on the virus
Date: Thu, 3 Nov 88 16:32:25 EST
... This program introduced itself through a bug in sendmail. At
these sites, sendmail was compiled and installed with a debugging
option turned on. As near as I can figure (I don't have access to
the sendmail sources), by giving a specific option to the "debug"
command in sendmail (there are lots of those, controlling what
exactly you get information about) you can cause it to execute a
command. As sendmail runs setuid to root, guess what privileges
the command is executed with. Right.
Apparently what the attacker did was this: he or she connected to
sendmail (ie, telnet victim.machine 25), issued the appropriate
debug command, and had a small C program compiled. (We have it.
Big deal.) This program took as an argument a host number, and
copied two programs -- one ending in q.vax.o and the other ending
in .sun.o -- and tried to load and execute them. In those cases
where the load and execution succeeded, the worm did two things
(at least): spawn a lot of shells that did nothing but clog the
process table and burn CPU cycles; look in two places -- the
password file and the internet services file -- for other sites it
could connect to (this is hearsay, but I don't doubt it for a
minute.) It used both individual .rhost files (which it found
using the password file), and any other remote hosts it could
locate which it had a chance of connecting to. It may have done
more; one of our machines had a changed superuser password, but
because of other factors we're not sure this worm did it.
This last part is still sketchy; I have the relevant sun.o file
and will take it apart to see just what it was supposed to do. As
of now, it appears there was no serious damage (just wasted CPU
cycles and system administrator time).
Two obvious points:
1. Whoever did this picked only on suns and vaxen. One site with a
lot of IRISes and two Crays (ie, NASA Ames) got bit on their Suns
and Vaxen, but the attempt to get the other machines didn't work.
2. This shows the sorry state of software and security in the UNIX
world. People should NEVER put a program with debugging hooks in
it, especially when the hook is (or can be made) to execute an
arbitrary command. But that is how the sendmail which was used
was distributed!
One more interesting point: initially, I thought an application of
the "principle of least privilege" would have prevented this
penetration. But the attacker used a world-writeable directory to
squirrel the relevant programs in, so -- in effect -- everything
could have been done by any user on the system! (Except the
superuser password change, of course -- if this worm did in fact
do it.)
I think the only way to prevent such an attack would have been to
turn off the debug option on sendmail; then the penetration would
fail. It goes to show that if the computer is not secure (and like
you, I don't believe there ever will be such a beastie), there is
simply no way to prevent a virus (or, in this case, a worm) from
getting into that system.
I know this is somewhat sketchy, flabby, and fuzzy, but it's all I
know so far. I'll keep you posted on developments ...
Matt
------------------------------------------------------------------
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From: bostic@okeeffe.Berkeley.EDU (Keith Bostic)
Subject: Virus (READ THIS IMMEDIATELY)
Date: 3 Nov 88 10:58:55 GMT
Subject: Fixes for the virus
Index: usr.lib/sendmail/src/srvrsmtp.c 4BSD
Description:
There's a virus running around; the salient facts. A bug in
sendmail has been used to introduce a virus into a lot of Internet
UNIX systems. It has not been observed to damage the host system,
however, it's incredibly virulent, attempting to introduce itself
to every system it can find. It appears to use rsh, broken
passwords, and sendmail to introduce itself into the target
systems. It affects only VAXen and Suns, as far as we know.
There are three changes that we believe will immunize your system.
They are attached.
Thanks to the Experimental Computing Facility, Center for Disease
Control for their assistance. (It's pretty late, and they
certainly deserved some thanks, somewhere!)
Fix:
First, either recompile or patch sendmail to disallow the `debug'
option. If you have source, recompile sendmail after first
applying the following patch to the module svrsmtp.c:
*** /tmp/d22039 Thu Nov 3 02:26:20 1988
--- srvrsmtp.c Thu Nov 3 01:21:04 1988
***************
*** 85,92 ****
"onex",CMDONEX,
# ifdef DEBUG
"showq",CMDDBGQSHOW,
- "debug",CMDDBGDEBUG,
# endif DEBUG
# ifdef WIZ
"kill",CMDDBGKILL,
# endif WIZ
--- 85,94 ----
"onex",CMDONEX,
# ifdef DEBUG
"showq",CMDDBGQSHOW,
# endif DEBUG
+ # ifdef notdef
+ "debug",CMDDBGDEBUG,
+ # endif notdef
# ifdef WIZ
"kill",CMDDBGKILL,
# endif WIZ
Then, reinstall sendmail, refreeze the configuration file, using
the command "/usr/lib/sendmail -bz", kill any running sendmail's,
using the ps(1) command and the kill(1) command, and restart your
sendmail. To find out how sendmail is execed on your system, use
grep(1) to find the sendmail start line in either the files
/etc/rc or /etc/rc.local
If you don't have source, apply the following patch to your
sendmail binary. SAVE A COPY OF IT FIRST, IN CASE YOU MESS UP!
This is mildly tricky -- note, some versions of strings(1), which
we're going to use to find the offset of the string "debug" in the
binary print out the offsets in octal, not decimal. Run the
following shell line to decide how your version of strings(1)
works:
/bin/echo 'abcd' | /usr/ucb/strings -o
Note, make sure the eight control 'G's are preserved in this line.
If this command results in something like:
0000008 abcd
your strings(1) command prints out locations in decimal, else it's
octal.
The patch script for sendmail. NOTE, YOUR OFFSETS MAY VARY!! This
script assumes that your strings(1) command prints out the offsets
in decimal.
Script started on Thu Nov 3 02:08:14 1988
okeeffe:tmp {2} strings -o -a /usr/lib/sendmail | egrep debug
0096972 debug
okeeffe:tmp {3} adb -w /usr/lib/sendmail
?m 0 0xffffffff 0
0t10$d
radix=10 base ten
96972?s
96972:debug
96972?w 0
96972:25701 = 0
okeeffe:tmp {4} ^D
script done on Thu Nov 3 02:09:31 1988
If your strings(1) command prints out the offsets in octal, change
the
line "0t10$d" to "0t8$d".
After you've fixed sendmail, move both /bin/cc and /bin/ld to
something
else. (The virus uses the cc and the ld commands to rebuild itself
to
run on your system.)
Finally, kill any processes on your system that don't belong
there. Suspicious ones have "(sh)" or "xNNNNNNN" where the N's are
random digits, as the command name on the ps(1) output line.
One more thing, if you find files in /tmp or /usr/tmp that have
names like "xNNNNNN,l1.c", or "xNNNNNN,sun3.o", or
"xNNNNNNN,vax.o" where the N's are random digits, you've been
infected.
------------------------------------------------------------------
-------
From: news@cs.purdue.EDU (News Knower)
Subject: Re: The virus
Date: 3 Nov 88 19:58:27 GMT
The patch from Keith Bostic in the last message is *not*
sufficient to halt the spread of the virus. We have discovered
from looking at the binaries that the virus also attempts to
spread itself via "rsh" commands to other machines. It looks
through a *lot* of files to find possible vectors to spread.
If you have a bunch of machines with hosts.equiv set or .rhosts
files, you should shut them *all* down at the same time after you
have fixed sendmail to prevent a further infestation. If you don't
clear out the versions in memory, you won't protect your other
machines.
The virus runs itself with the name "sh" and then overwrites argv,
so if a "ps ax" shows any processes named "(sh)" without a
controlling tty, you have a problem. Due to the use of other uids
from rsh, don't make any conclusions if the uid is one of your
normal users.
Also, check your mailq (do a mailq command). If you see any
entries that pipe themselves through sed and sh, delete them from
the queue before
you restart your machines.
Non-internet sites do not need to worry about this virus (for
now!), but be aware that mail and news may not be flowing
everywhere for some time -- many sites are disconnecting from the
Internet completely until the virus is contained.
------------------------------------------------------------------
-------
From: Gene Spafford
Subject: Updated worm report
Date: Fri, 04 Nov 88 00:27:54 EST
This is an updated description of how the worm works (note: it is
technically a worm, not a virus, since it does not attach itself
to other code {that we know about}):
All of our Vaxen and some of our Suns here were infected with the
worm. The worm forks repeated copies of itself as it tries to
spread itself, and the load averages on the infected machines
skyrocketed. In fact, it got to the point that some of the
machines ran out of swap space and kernel table entries,
preventing login to even see what was going on!
The worm seems to consist of two parts. The way that it works is
as follows:
1) Virus running on an infected machine opens a TCP connection to
a victim machine's sendmail, invokes debug mode, and submits a
version of itself as a mail message.
*OR* it uses rsh to create itself on the remote machine through an
account requiring no password (due to hosts.equiv or .rhosts
entries).
*OR* it gets in via a bug in fingerd *OR* it uses telnet (more on
this later).
Using the sendmail route, it does something like:
From: /dev/null
To: "|sed -e 1,/^$/d | sh; exit 0"
