Instructions for removing Sasser infection and patching affected machines
From: Bill Sanderson (Bill_Sanderson_at_msn.com.plugh.org)
Date: 05/04/04
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Date: Tue, 4 May 2004 10:27:49 -0400
Instructions for patching and cleaning vulnerable Windows 2000 and
Windows XP systems:
Vulnerable Windows 2000 and Windows XP machines may have the LSASS.EXE
process crash every time a malicious worm packet targets the vulnerable
machine which can occur very shortly after the machine starts up and
initializes the network stack.
When cleaning a machine that is vulnerable to the Sasser worm it is
necessary to first prevent the LSASS.EXE process from crashing, which in
turn causes the machine to reboot after a 60 second delay. This reboot
cannot be aborted on Windows 2000 platforms using the Shutdown.exe or
psshutdown.exe utilities and can interfere with the downloading and
installation of the patch as well as removal of the worm.
1. To prevent LSASS.EXE from shutting down the machine during the
cleaning process:
a. Unplug the network cable from the machine
b. If you are running Windows XP you can enable the built-in
Internet Connection Firewall using the instructions found here: Windows XP
http://support.microsoft.com/?id=283673 and then plug the machine back
into the network and go to step 2.
c. If you are running Windows 2000, you won't have a built-in
firewall and must use the following work-around to prevent LSASS.EXE from
crashing.
This workaround involves creating a read-only file named 'dcpromo.log'
in the "%systemroot%\debug" directory. Creating this read-only file will
prevent the vulnerability used by this worm from crashing the LSASS.EXE
process.
i. NOTE: %systemroot% is the variable that contains the
name of the Windows installation directory. For example if Windows was
installed to the "c:\winnt" directory the following command will create a
file
called dcpromo.log in the c:\winnt\debug directory. The following commands
must be typed in a command prompt (i.e. cmd.exe) exactly as they are written
below.
1. To start a command shell, click Start and then click run and
type 'cmd.exe' and press enter.
2.Type the following command:
echo dcpromo >%systemroot%\debug\dcpromo.log
For this workaround to work properly you MUST make the file
read-only by typing the following command:
3. attrib +R %systemroot%\debug\dcpromo.log
2. After enabling the Internet Connection Firewall or creating the
read-only dcpromo.log you can plug the network cable back in and you must
download
and install the MS04-011 patch from the MS04-011 download link for the
affected machines operating system before cleaning the system. If the
system is
cleaned before the patch is installed it is possible that the system
could get re-infected prior to installing the patch.
a. Here is the URL for the bulletin which contains the links to the
download location for each patch:
http://www.microsoft.com/technet/security/bulletin/ms04-011.mspx
b. If your machine is acting sluggish or your Internet connection
is slow you should use Task Manager to kill the following processes and
then try downloading the patch again (press the Ctrl + Alt + Del keys
simultaneously and select Task Manager):
i. Kill any process ending with '_up.exe' (i.e. 12345_up.exe)
ii. Kill any process starting with 'avserv' (i.e. avserve.exe,
avserve2.exe)
iii. Kill any process starting with 'skynetave' (i.e. skynetave.exe)
iv. Kill hkey.exe
v. Kill msiwin84.exe
vi. Kill wmiprvsw.exe
1. Note there is a legitimate system process called 'wmiprvse.exe'
that does NOT need to be killed.
c. allow the system to reboot after the patch is installed.
3. Run the Sasser cleaner tool from the following URL:
a. For the on-line ActiveX control based version of the cleaner you
can run it directly from the following URL:
http://www.microsoft.com/security/incident/sasser.asp
b. For the stand-alone download version of the cleaner you can
download it from the following URL:
4. Determine if the machine has been infected with a variant of the
Agobot worm which can also get on the machine using the same method as the
Sasser worm.
a. To do this run a full antivirus scan of your machine after
ensuring your antivirus signatures are up to date.
b. If you do NOT have an antivirus product installed you can visit
HouseCall from TrendMicro to perform a free scan using the following
URL:
http://housecall.trendmicro.com/
If you have any questions regarding the security updates or its
implementation after reading the above listed bulletin you should
contact Product Support Services in the United States at 1-866-PCSafety
(1-866-727-2338). International customers should contact their local
subsidiary.
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