Backdoor:W32/IRCBot.BNZ

This IRCBot connects to an IRC server at fixed.milan-fans.com at port 2233 for instructions.

A backdoor is a trojan that allows unauthorized access to a computer system. It is a remote access tool that allows a hacker to gain access to a compromised computer through the "back door" that the trojan has opened (usually a TCP or UDP port).

Usually a backdoor is a standalone file that installs itself to the system after it is run and then remains active in the memory listening on specific network ports for commands from the remote host.

IRCBot.BNZ is downloaded from malicious sites. This download can be initiated by a shellcode executed via an unpatched MS04-011 vulnerability on target machines.

When first run copies of the malware will be created in %WINDOWS%\System32\spool.exe as and C:\%name%.exe where %name% is a random six-digit number.

Note: %WINDOWS% represents the default Windows installation folder.

Launchpoints/Autostart:

IRCBot.BNZ uses the following registry entries to run on startup:

• HKCU\Software\Microsoft\Windows\CurrentVersion\RunMicrosoft Update = "C:\WINDOWS\system32\spool.exe
• HKLM\Software\Microsoft\Windows\CurrentVersion\RunMicrosoft Update = "C:\WINDOWS\system32\spool.exe

Changes the following registry entries:

• HKLM\Software\Microsoft\OleEnableDCOM = "N"
• HKLM\System\CurrentControlSet\Control\Lsarestrictanonymous = "1"
• HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinlogonShell = "EXPLORER.EXE\%name%.exe

Note: %name% represents the name of the file previously dropped by the malware.

Backdoor Functionality:

IRCBot.BNZ has IRC backdoor functionality. With this functionality a remote attacker may:

• Download and execute arbitrary files
• Scan for vulnerable ports on target machines
• Attempt to infect a target vulnerable machine
• Update the bot on the infected machine

IRCBot.BNZ uses an MS04-011 LSASS exploit to inject and execute shellcode on the target machine. Please refer to the following Microsoft website for details on the vulnerability and solutions.

• http://www.microsoft.com/technet/security/bulletin/MS04-011.mspx

Payload

IRCBot.BNZ may download a file from www.[REMOVED].net/c8563/staff.exe which as of February 22, 2008 is a copy of the same malware.