Last revised: August 23, 2001
Source: CERT/CC
A complete revision history can be found at the end of this file.
Systems Affected
Overview
"W32/Sircam" is malicious code that spreads through email and potentially through unprotected network shares. Once the malicious code has been executed on a system, it may reveal or delete sensitive information.
As of 10:00EDT(GMT-4) Jul 25, 2001 the CERT/CC has received reports
of W32/Sircam from over 300 individual sites.
W32/Sircam can infect a machine in one of two ways: The virus can appear in an email message written in either English
or Spanish with a seemingly random subject line. All known versions
of W32/Sircam use the following format in the body of the
message:I. Description
Propagation Via Email
| English | Spanish |
Hi! How are you?
[middle line]
See you later. Thanks
|
Hola como estas ?
[middle line]
Nos vemos pronto, gracias.
|
Where [middle line] is one of the following:
| English |
I send you this file in order to have your advice I hope you like the file that I sendo you I hope you can help me with this file that I send This is the file with the information you ask for |
| Spanish |
Te mando este archivo para que me des tu punto de vista Espero te guste este archivo que te mando Espero me puedas ayudar con el archivo que te mando Este es el archivo con la informacion que me pediste |
Users who receive copies of the malicious code through electronic mail might recognize the sender. We encourage users to avoid opening attachments received through electronic mail, regardless of the sender's name, without prior knowledge of the origin of the file or a valid digital signature.
The email message will contain an attachment whose name matches the subject line and has a double file extension (e.g. subject.ZIP.BAT or subject.DOC.EXE). The CERT/CC has confirmed reports that the first extension may be .DOC, .XLS, or .ZIP. Anti-virus vendors have referred to additional extensions, including .GIF, .JPG, .JPEG, .MPEG, .MOV, .MPG, .PDF, .PNG, and .PS. The second extension will be .EXE, .COM, .BAT, .PIF, or .LNK. The attached file contains both the malicious code and the contents of a file copied from an infected system.
When the attachment is opened, the copied file is extracted to both the %TEMP% folder (usually C:\WINDOWS\TEMP) and the Recycled folder on the affected system. The original file is then opened using the appropriate default viewer while the infection process continues in the background.
It is possible for the recipient to be tricked into opening this malicious attachment since the file will appear without the .EXE, .BAT, .COM, .LNK, or .PIF extensions if the "Hide file extensions for known file types" is enabled in Windows. See IN-2000-07 for additional information on the exploitation of hidden file extensions.
W32/Sircam includes its own SMTP client capabilities, which it uses to propagate via email. It determines its recipient list by recursively searching for email addresses contained in all *.wab (Windows Address Book) files in the %SYSTEM% folder. Additionally, it searches the folders referred to by
- HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders\Cache
W32/Sircam first attempts to send messages using the default email settings for the current user. If the default settings are not present, it appears to use one of the following SMTP relays:
- prodigy.net.mx
- NetBIOS name for 'MAIL'
- mail.<defaultdomain> (e.g., mail.example.org)
- dobleclick.com.mx
- enlace.net
- goeke.net
Propagation Via Network Shares
In addition to email-based propagation, analysis by anti-virus vendors suggests that W32/Sircam can spread through unprotected network shares. Unlike the email propagation method, which requires a user to open an attachment to infect the machine, propagation of W32/Sircam via network shares requires no human intervention.
If W32/Sircam detects Windows networking shares with write access, it
- copies itself to \\[share]\Recycled\SirC32.EXE
- appends "@ win\Recycled\SirC32.exe" to AUTOEXEC.BAT
If the share contains a Windows folder, it also
- copies \\[share]\Windows\rundll32.exe to \\[share]\Windows\run32.exe
- copies itself to \\[share]\Windows\rundll32.exe
- when virus is executed from rundll32.exe, it calls run32.exe
Infection process
- When installed on a victim machine, W32/Sircam installs a copy of
itself in two hidden files:
- %SYSTEM%\SCam32.exe
- Recycled\SirC32.exe
Installing in Recycled may hide it from anti-virus software since some do not check this folder by default.
Based on external analyses, there is also a probability that W32/Sircam will copy itself to the %SYSTEM% folder as ScMx32.exe. In that case, another copy is created in the folder referred to by HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders\Startup (the current user's personal startup folder). The copy created in that location is named Microsoft Internet Office.exe. When the affected user next logs in, this copy of W32/Sircam will be started automatically.
- The registry entry HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunServices\Driver32 is set to %SYSTEM%\SCam32.exe so that W32/Sircam will run automatically at system startup.
- The registry entry HKEY_CLASSES_ROOT\exefile\shell\open\command is set to "C:\Recycled\SirC32.exe" "%1" %*", causing W32/Sircam to execute whenever another executable is run.
- A new registry entry, HKEY_LOCAL_MACHINE\Software\SirCam, is created to store data required by W32/Sircam during execution.
- W32/Sircam searches for filenames with .DOC, .XLS, .ZIP
extensions in the folders referred to by
- HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders\Personal
- HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders\Desktop
While the personal folder may vary with configuration, it is often set to \My Documents or \Windows\Profiles\%username%\Personal. A list of these files is stored in %SYSTEM%\scd.dll.
- W32/Sircam attaches its own binary to selected files it finds and stores the combined file in the Recycled folder.
II. Impact
W32/Sircam can have a direct impact on both the computer which was infected as well as those with which it communicates over email.- Breaches of confidentiality: The malicious code will at a minimum search through select folders and mail potentially sensitive files. This form of attack is extremely serious since it is one from which it is impossible to recover. Once a file has been publicly distributed, any potentially sensitive information in it cannot be retracted.
- Limit Availibility (Denial of Service)
- Fill entire hard drive: Based on external analyses, on any
given day, there is a probability that it will create a file named
C:\Recycled\sircam.sys which consumes all free space on
the C: drive. A full disk will prevent users from saving
files to that drive, and in certain configurations impede system-level
tasks (e.g., swapping, printing).
- Propagation via mass emailing: W32/Sircam will attempt
to propagate by sending itself through email to addresses obtained as described above.
This propagation can lead to congestion in mail
servers that may prevent them from functioning as expected.
NOTE: Since W32/Sircam uses native SMTP routines connecting to pre-defined mail servers, propagation is independent of the mail client software used.
- Fill entire hard drive: Based on external analyses, on any
given day, there is a probability that it will create a file named
C:\Recycled\sircam.sys which consumes all free space on
the C: drive. A full disk will prevent users from saving
files to that drive, and in certain configurations impede system-level
tasks (e.g., swapping, printing).
- Loss of Integrity: Published reports indicate that on October 16 there is a reasonable probability that W32/Sircam will attempt to recursively delete all files from the drive on which Windows is installed (typically C:).
III. Solution
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.
Exercise Caution When Opening Attachments
Exercise caution when receiving email with attachments. Users should never open attachments from an untrusted origin, or ones that appear suspicious in any way. Finally, cryptographic checksums should also be used to validate the integrity of the file.
The effects of this class of malicious code are activated only when the file in question is executed. Social engineering is typically employed to trick a recipient into executing the malicious file. The best advice with regard to malicious files is to avoid executing them in the first place. The following tech tip offers suggestions as to how to avoid them:
Filter the Email or use a Firewall
Sites can use email filtering techniques to delete messages containing subject lines known to contain the malicious code, or they can filter all attachments.
Likewise, a firewall or border router can be used to stop the W32/Sircam outbound SMTP connections to mail servers outside of the local network. This filtering strategy will prevent further propagation of the worm from a particular host when the local mail configuration is not used.
Appendix A. - Vendor Information
Aladdin Knowledge Systems
Central Command, Inc.
Command Software Systems
Computer Associates
Data Fellows Corp
McAfee
Norman Data Defense Systems
Panda Software
Proland Software
Sophos
Symantec
Trend Micro
You may wish to visit the CERT/CC's Computer Virus Resources Page located at:
http://www.cert.org/other_sources/viruses.html
Authors: Roman Danyliw, Chad Dougherty, Allen Householder
Copyright 2001 Carnegie Mellon University.
Revision History
Jul 25, 2001: Initial release Jul 25, 2001: The virus does NOT search the Desktop registry key for address books. Additionally, correct EST to EDT. Aug 23, 2001: Updated contact information