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From: Stoll@DOCKMASTER.ARPA
Subject: Virus on the Arpanet - Milnet
Date: Thu, 3 Nov 88 06:46 EST
Re Arpanet "Sendmail" Virus attack November 3, 1988
Hi Gang!
It's now 3:45 AM on Wednesday 3 November 1988. I'm tired, so don't
believe everything that follows...
Apparently, there is a massive attack on Unix systems going on right
now.
I have spoken to systems managers at several computers, on both the east
& west coast, and I suspect this may be a system wide problem.
Symptom: hundreds or thousands of jobs start running on a Unix system
bringing response to zero.
Systems attacked: Unix systems, 4.3BSD unix & variants (eg: SUNs) any
sendmail compiled with debug has this problem. See below.
This virus is spreading very quickly over the Milnet. Within the past 4
hours, I have evidence that it has hit >10 sites across the country,
both Arpanet and Milnet sites. I suspect that well over 50 sites have
been hit. Most of these are "major" sites and gateways.
Method:
Apparently, someone has written a program that uses a hole in SMTP
Sendmail utility. This utility can send a message into another program.
Step 1: from a distant Milnet host, a message is sent to Sendmail
to fire up SED, (SED is an editor) This is possible in certain
versions of sendmail (see below).
2: A 99 line C program is sent to SED through Sendmail.
3: The distant computer sends a command to compile this C program.
4: Several object files are copied into the Unix computer.
There are 3 files: one targeted to Sun
one targeted to SUN-3
one targeted to vax (ultrix probably, not vms)
5: The C program accepts as address other Milnet sites
6: Apparently, program scans for other Milnet/arpanet addresses and
repeats this process.
The bug in Sendmail:
When the Unix 4.3 BSD version of Sendmail is compiled with the Debug
option, there's a hole in it.
Most Unix systems (BSD 4.3 and Suns) apparently do not have this bug.
It exists only where the system manager recompiled Sendmail and enabled
debugging.
This is bad news.
Cliff Stoll dockmaster.arpa
----------------------------------------------------------------------
From: Gene Spafford <spaf@purdue.edu>
Subject: More on the virus
Date: Thu, 03 Nov 88 09:52:18 EST
All of our Vaxen and some of our Suns here were infected with the virus.
The virus 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 virus seems to consist of two parts. I managed to grab the source
code for one part, but not the main component (the virus cleans up after
itself so as not to leave evidence). 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 gets a shell.
2) The shell creates a file in /tmp named $,l1.c (where the $ gets
replaced by the current process id) and copies code for a "listener" or
"helper" program. This is just a few dozen lines long and fairly
generic code. The shell compiles this helper using the "cc" command
local to the system.
3) The helper is invoked with arguments pointing back at the infecting
virus (giving hostid/socket/passwords as arguments).
4) The helper then connects to the "server" and copies a number of files
(presumably to /tmp). After the files are copied, it exec's a shell
with standard input coming from the infecting virus program on the other
end of the socket.
From here, I speculate on what happens since I can't find the source to
this part lying around on our machines:
5) The newly exec'd shell attempts to compile itself from the files
copied over to the target machine. I'm not sure what else the virus
does, if anything -- it may also be attempting to add a bogus passwd
file entry or do something to the file system. The 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 deug 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
------------------------------------------------------------------------
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 <spaf@purdue.edu>
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.