Worm:W32/Sircam is a mass mailing e-mail worm with the ability to through Windows Network shares.
Sircam is particularly menacing because it includes a routine to add a document from the infected computer to the e-mail messages it sends out to new victims. The document added is chosen from one of the documents in the user's 'My Documents' folder; this behavior may result in confidential material being released.
The worm's body is 137216 bytes long but when it comes as an e-mail attachment, it appears larger in size due to the document attached to its body.
Sircam sends e-mails with variable user names and subject fields, and attaches user documents with double extensions (such as .doc.pif or .xls.lnk) to them. Messages sent by Sircam look like this:
When a Sircam-infected e-mail attachment is opened it shows the document it picked up from the sender machine's. The file is displayed with the appropriate program according to its extension:
This effectively disguises the worm's activity. While the user is checking the document the system get infected (as described above).
When the worm runs on a clean system it copies itself to different locations with different names. The worm copies itself as 'SirC32.exe' to \Recycled\ folder. The default EXE file startup Registry key:
is changed to '""[windows_drive]\recycled\SirC32.exe" "%1" %*"'. This is done to activate a worm's copy every time an EXE file is started. Since the recycled folder name is hard coded, the worm does not work on machines with NTFS filesystem. Most Windows NT and 2000 systems are installed on NTFS. The worm copies itself as 'SCam32.exe' in the System directory. The worm then creates a startup key for this file in the Registry to be started during all Windows sessions:
The worm copies itself as 'rundll32.exe' file to Windows directory. The original 'rundll32.exe' file is renamed to 'run32.exe'. This copy exists only if a computer got infected through a network share (see below).
Sometimes (once out of 33 cases) the worm places its copy to Windows directory with the 'ScMx32.exe' name. In this case another copy of the worm is created in the current user's personal startup folder as 'Microsoft Internet Office.exe'. This copy will be started when a user who got infected logs into a system.
The worm has two payloads. On 16th of October, in one case out of 20, it deletes everything from the drive where Windows is installed. On any other day, in one of 50 cases, it fills up the drive where Windows is installed. In this case it creates a file called ':\recycled\sircam.sys' and continuously fills it with one of below given text strings until the hard drive space is consumed.
Fortunately neither of these payloads work due to bugs in the trigger routine. The random number generator in not initialized in the beginning, so the worm will not activate it's payloads on 16th of October or on any other day.
The e-mails sent by Sircam have the following characteristics.
The body text uses the following first line
One of the following as a second line:
And concludes with the following last line:
If a system's language is set to Spanish, the worm sends messages in Spanish, with the first line of the body text as:
The second line being one of the following:
And the last line:
To find other machines to infect, the worm searches the Windows Address Book ('*.wab files) to collect e-mail addresses. It also tries to look for e-mail addresses in \Temporary Internet Files\ folder ('sho*', 'get*', 'hot*', '*.html'). If a user has a working e-mail account the worm reads the its setting. Otherwise the '[username]@prodigy.mx.net' is used as the default sender's address and 'prodigy.net.mx' is used for the SMTP server name.
The worm has its own SMTP engine and it sends out messages using this engine.
The worm collects a list of files with certain extensions ('.DOC', '.XLS', '.ZIP') into fake DLL files named 'sc*.dll'. The worm then sends itself out with one of the document files it found in the user's 'My Documents' folder.
The attached file has the name of a picked document file with a double extension like '.DOC.EXE', '.XLS.PIF'. The '.COM', '.BAT', '.PIF' and '.LNK' are used as second (executable) extensions. Since the worm can pick any of the user's personal document it might send out confidential information.
This worm also uses Windows network shares to spread.
When doing this, it first enumerates all the network shares available to the infected computer. If there there is a writeable \recycled\ folder on a share, a copy of the worm is put to \\[share]\recycled\' folder as 'SirCam32.exe' file.
The \\[share]\autexec.bat file is appended with an extra line: '@win \recycled\SirC32.exe', so next time when an infected computer is rebooted the worm will be started.
The worm also copies itself as 'rundll32.exe' file to Windows directory of a remote system. The original 'rundll32.exe' file is copied to 'run32.exe' before that.