Full description from f-secure
From: Toby Henderson (TobyH@PERFECTINFO.COM)Date: 09/19/01
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Message-ID: <D55AAE7EC7D4D3119B67009027E5B96457E1F8@SULPHUR> Date: Wed, 19 Sep 2001 02:07:41 +0100 From: Toby Henderson <TobyH@PERFECTINFO.COM> Subject: Full description from f-secure To: NTBUGTRAQ@LISTSERV.NTBUGTRAQ.COM
Taken from the F-secure web site
http://www.f-secure.com/v-descs/nimda.shtml
NAME:Nimda
ALIAS:W32/Nimda.A@mm
ALIAS:W32/Nimda@mm, I-Worm.Nimda
SIZE:57344
This worm was found on September 18th, 2001. It quickly spread around the
world.
Nimda is a complex virus with a mass mailing worm component which spreads
itself in attachments named README.EXE. If affects Windows 95, Windows 98,
Windows Me, Windows NT 4 and Windows 2000 users.
Nimda is the first worm to modify existing web sites to start offering
infected files for download. Also it is the first worm to use normal end
user machines to scan for vulnerable web sites. This technique enables Nimda
to easily reach intranet web sites located behind firewalls - something
worms such as Code Red couldn't directly do.
Nimda uses the Unicode exploit to infect IIS web servers. This hole can be
closed with a Microsoft patch, downloadable from:
http://www.microsoft.com/technet/security/bulletin/ms00-078.asp
TECHNICAL DETAILS
Nimda is a complex mass-mailer, network worm and virus. It is a 57kb PE DLL
file with an EXE extension.
When run the worm first checks the name of the file it was run from. If the
name of worm's file is ADMIN.DLL, the worm creates a mutex with
'fsdhqherwqi2001' name, copies itself as MMC.EXE into \Windows\ directory
and starts this file with '-qusery9bnow' command line. If the worm is
started from README.EXE file (or a file that has more than 5 symbols in its
name and EXE extension) the worm copies itself to temporary folder with a
random name and runs itself there with '-dontrunold' command line option.
If the worm is run for the first time (as README.EXE) it loads itself as a
library, looks for some resource there and checks its size. If the resource
size is less than 100, the worm unloads itself, otherwise the worm checks if
it was launched from a hard drive and deletes its file in case it was
launched from other type of media. If the worm's file that is delete is
locked, the worm creates WININIT.INI file that will delete the worm's file
on next Windows startup. If the worm was launched from a hard drive, it
checks one of its resources, extracts it to a file and launches it. Checking
the resource size is done to be able to detect if a worm runs from and
infected EXE file. In this case the original executable part is extracted
and run by the worm to disguise its presence.
Then the worm gets current time and generates a random number. After
performing multiplication and division with this number the worm checks the
result. If a result is bigger than worm's counter, the worm starts to search
and delete README*.EXE files in temporary folder.
The worm tries to create the
[SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces] key in the
Registry. It also queries 'NameServer' value from
[System\CurrentControlSet\Services\VxD\MSTCP] key. After that the worm
updates its resources and deletes and re-creates its file. If the file is
locked, the worm creates WININIT.INI file that will delete the previously
locked file on next Windows startup.
After that the worm prepares its MIME-encoded copy by extrating a
pre-defined multi-partite message from its body and appending its
MIME-encoded copy to it. The file with a random name is created in temporary
folder.
The worm looks for EXPLORER process, opens it and assigns its process as
remote thread of Explorer. Then the worm gets API creates a mutex with
'fsdhqherwqi2001' name, startups Winsock services, gets an infected computer
(host) info and sleeps for some time. When resumed, the worm checks what
platform it is running. If it is running on NT-based system, it compacts its
memory blocks to occupy less space in memory and copies itself as LOAD32.EXE
to Windows system directory. Then it modifies SYSTEM.INI file by adding the
following string after SHELL= variable in [Boot] section:
explorer.exe load.exe -dontrunold
This will start the worm's copy every time Windows starts. The worm also
copies itself as RICHED32.DLL file to system folder and sets hidden and
system attributes to this file as well as to LOAD.EXE file. Then the worm
enumerates shared network resources and scarts to recursively scan files on
remote systems. If the worm finds an EXE file on a remote system, it reads
the file, deletes it and then writes a new file where the worm body is
placed first and the original EXE file is present as a resource. Later when
this affected file will be run, the worm will extract the EXE file resource
and run it. The worm checks the file name for 'WinZip32.exe' and doesn't
affect this file if it is found.
When searching for files in remote systems the worm collects names of DOC
files and then copies its file to folders where DOC files are located with
RICHED32.DLL name. The copied file has system and hidden attributes. This is
done to increase the chances of worm activation on remote systems as
Windows' original RICHED32.DLL component is used to open OLE files. But
instead the worm's RICHED32.DLL file will be launched as Windows first
checks current directory for needed DLLs.
Also when the worm browsing the remote computers' directories it creates
.EML and .NWS (rarely) files that have the names of document files that the
worm could find on a remote system. These .EML and .NWS files are worm's
multi-partite messages with a worm MIME-encoded in them. When scanning the
worm can also delete the .EML and .NWS files it previously created.
The worm adjusts the properties of Windows Explorer, it accesses
[Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced] key and
adjusts 'Hidden', 'ShowSuperHidden' and 'HideFileExt' keys. This affects
Windows' (especially ME and 2000) ability to show hidden files - worm's
files will not be seen in Explorer any more.
After that the worm adds a 'guest' account to infected system account list,
activates this account, adds it to 'Administrator' and 'Guests' groups and
shares C:\ drive with full access priviledges. The worm also deletes all
subkeys from
[SYSTEM\CurrentControlSet\Services\lanmanserver\Shares\Security] key to
disable sharing security.
The worm accesses [SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths] key
reads subkeys from there and affects all files listed in the subkeys the
same way it does affect remote EXE files (see above). The worm doesn't only
infect WinZip32.exe file. Also the worm reads user's personal folders from
[Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders] key and
infects files in these folders as well.
Finally the worm starts to search local hard drives for HTML, .ASP, and .HTM
files and also for files with 'DEFAULT', 'INDEX', 'MAIN' and 'README' words
in their filenames and if such files are found, the worm creates README.EML
file (which is the multi-partite message with MIME-encoded worm) in the same
directory and adds a small JavaScript code to the end of found files. That
JavaScript code would open README.EML file when the infected HTML file is
loaded by a web browser. As a result the MIME-encoded wor m will get
activated because of a security hole and a system will get infected. It
should be noted that the worm will not always do the above described
operation, it depends on a random number the worm generates prior to this
action.
The worm's file runs from a minimized window when downloaded from an
infected webserver. This technique affects users who are browsing the web
with Internet Explorer 5.0 or 5.01.
E-Mail spreading:
The worm searches trough all the '.htm' and '.html' file in the Temporary
Internet Files folder for e-mail addresses. It reads trough user's inbox and
collects the sender addresses. When the address list is ready it uses it's
own SMTP engine to send the infected messages.
IIS spreading:
The worm uses backdoors on IIS servers such as the one CodeRed II installs.
It scans random IP addresses for these backdoors. When a host is found to
have one the worm instructs the machine to download the worm code
(Admin.dll) from the host used for scanning. After this it executes the worm
on the target machine this way infecting it.
The worm has a copyright text string that is never displayed:
Concept Virus(CV) V.5, Copyright(C)2001 R.P.China
It should be said that the worm has bugs that cause crashes or inability to
spread itself in certain conditions.
F-Secure Anti-Virus detects the worm with updates released at September
18th, 2001 19:20 EET.
[Analysis: Katrin Tocheva, Gergely Erdelyi, Alexey Podrezov, Sami Rautiainen
and Mikko Hypponen; F-Secure Corp.; September 18th, 2001]
Good luck
Toby
Toby Henderson
Technology Manager
Perfect Information Ltd
Michael House
35 Chiswell Street
London, EC1Y 4SE
Tel: +44 (0)20 7892 4294
Fax: +44 (0)20 7892 4201
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