Internet Security Threats

Trojan.Mdropper.V is a Trojan horse that drops additional malware detected as Trojan.Dropper on the compromised computer. It exploits the Microsoft Word Malformed Object Pointer Remote Code Execution Vulnerability (BID 18037).

It has been reported that the Trojan may arrive as an attachment in spammed email or may be pointed to by a URL in the email.

When Trojan.Mdropper.V is executed, it creates and executes the following file:
%Temp%\ahah.exe - detected as Trojan.Dropper

When %Temp%\ahah.exe is executed, it creates the following files:

%Temp%\sav.exe - detected as Backdoor.Trojan
%Temp%\temp.doc - a clean Microsoft Word file
C:\Program Files\Adobe\acrobat.exe - identical to %Temp%\sav.exe

The Trojan then opens %Temp%\temp.doc and executes %Temp%\sav.exe.

Next, the Trojan creates the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\{41035B86-B82C-CB7C-92D8-2B322604630E}\"stubpath" = "C:\Program Files\Adobe\acrobat.exe s"
HKEY_LOCAL_MACHINE\SOFTWARE\acrobat\"nck" = "[BINARY VALUE]"
HKEY_CURRENT_USER\Software\acrobat\"klg" = "0"

The Trojan uses the file %Temp%\sav.exe to open a back door on the compromised computer that connects to the data.happysunrider.com domain on TCP port 80 allowing a remote attacker to perform the following actions:
Capture screen images on the compromised computer
List running proccess
Terminate running processes
Gather system info, including: OS, CPU speed, free memory, uptime, free disk space
Log keystrokes
Read, write, and create files
List open windows

The Trojan exploits the following vulnerability:
Microsoft Word Malformed Object Pointer Remote Code Execution Vulnerability (BID 18037)

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
• Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. Perform a forensic analysis and restore the computers using trusted media.
• Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.