Original release date: July 25, 2001
Last revised: August 23, 2001Source: CERT/CC
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.
I. Description
W32/Sircam can infect a machine in one of two ways:- When executed by opening an email attachment containing the malicious code
- By copying itself into unprotected network shares
Propagation Via Email
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:| English | Spanish |
Hi! How are you?
[middle line]
See you later. Thanks
| Hola como estas ?
[middle line]
Nos vemos pronto, gracias.
|
| 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 |
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 Recycledfolder 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
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 byHKEY_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
- 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.
- 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.
