Email-Worm:W32/Sober.J

The worm is written in Visual Basic. The worm's file is a UPX packed PE executable about 43 kilobytes long. The unpacked worm's file size is over 140 kilobytes. The worm adds random garbage to the end of its file every time it installs itself on a computer.

Installation to system

When the worm's file is started it opens Write text editor with the following text as a decoy:

Then the worm installs itself to system. It copies itself to Windows System folder with a semi-randomly generated name and EXE extension. The following text strings are used to generate the file name of the worm's executable:

sys host dir expoler win run log 32 disc crypt data diag spool service smss32

After that the worm creates startup keys for its file in Windows Registry. The key names are also semi-randomly generated from the above given list. The following keys are created:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

During its installation cycle the worm creates the following files in Windows System folder:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

These files have zero length and they are used to disable previous variants of Sober if they are installed on an infected computer.

Additionally the worm creates the following files:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

The 'dgsfzipp.gmx' file is a MIME-encoded ZIP archive with the worm's file. This file will be used for spreading of the worm in email messages. The 'datamx.dam' file contains email addresses collected by the worm on an infected computer.

Additionally the worm creates the 'read.me' file that contains the following text:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

Spreading in emails

The worm sends email messages with English and German texts and its file attached. The attachment is a ZIP archive containing the worm's executable. The worm composes two different email messages. Here's an example of an English message sent by the worm:

Before spreading the worm scans files with certain extensions on all hard disks to harvest email addresses. Files with the following extensions are scanned:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

The found email addresses and user names are saved in the file that the worm creates in Windows System folder:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

When the worm is active in memory it blocks access to these files as well as to its MIME-encoded files and its executable file.

The worm ignores email addresses that contain any of the following substrings:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

If the worm sends infected messages to domains with suffixes '.de', '.ch', '.at', it composes a message in German, otherwise English message is composed.

The worm composes the following English message:

Subject:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

Body:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

Attachment:

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

or

[HKCU\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe" [HKLM\Software\Microsoft\Windows\CurrentVersion\Run] "" = "%WinSysDir%\.exe"

The ZIP archive sent by the worm contains the worm's executable file with the following name:

mail_text-info.txt .pif

The worm does not use any exploits to start its file automatically on a recipient's system.

Deactivation

The worm does not infect a computer if the file with the 'stopruns.zhz' name is found in Windows System folder.