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Email-Worm:W32/Sober.H

Classification

Category: Malware

Type: -

Aliases: Sober.H, I-Worm.Sober.h

Summary


Sober.H appeared on June 11th, 2004. This Sober variant doesn't spread itself in emails. Instead, it mass-mails political statements. It might have been downloaded to computers already infected by earlier Sober variant, Sober.G for example.

Removal


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Technical Details


Sober.H is written in Visual Basic. Its file is a PE executable 59747 bytes long, packed with UPX file compressor. Sober.H has its own SMTP engine.

Installation to system

Sober.H's file is started 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 Sober's executable:

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

After that Sober.H 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 Sober.H 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.

Sending emails

Sober.H sends different email messages with political statements. It doesn't attach itself to these messages.

Before spamming Sober.H 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 these 2 files that Sober.H creates in Windows System folder:

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

When Sober.H is active in memory it blocks access to these files as well as to its executable file.

Sober.H 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"
 
Payload

Sober.H can download and activate an executable file from the following website:

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

The name of the downloaded executable file is 'winhlpx32ll.exe'.

Deactivation of Sober.H

Sober.H periodically looks for a file named 'sysmms32.lla' and it this file is found, it uninstalls itself from memory. Moreover, if this file is present in Windows System folder, Sober.H does not install itself to a system.