Trojan-Downloader:W32/Chymine.A

Summary

A trojan that secretly downloads malicious files from a remote server, then installs and executes the files.

Disinfection & Removal

Allow F-Secure Anti-Virus to disinfect the relevant files.

For more general information on disinfection, please see Removal Instructions.

Technical Details

Trojan-Downloader:W32/Chymine.A exploits a recently discovered vulnerability (CVE-2010-2568) in Microsoft Window's handling of shortcut icons in order to execute a file and drop a keylogger component on the affected machine. The keylogger is capable of capturing keyboard strokes entered into the infected system.For more information on the vulnerability, please refer to Microsoft Security Bulletin 2286198 (http://www.microsoft.com/technet/security/advisory/2286198.mspx).This malware is also mentioned in our Labs Weblog:

• LNK Vulnerability: Chymine, Vobfus, Sality and Zeus

Execution

The actual exploit is performed by a shortcut (.LNK) file detected as Exploit:W32/Wormlink.B. On execution, the exploit loads the downloader component (the actual file detected as Trojan-Downloader:W32/Chymine.A) from a shared folder shared over the Internet:

• \205.209.171.[...]\DlaT\GdWbpvo.dll

Which in turn downloads an EXE file (detected as Trojan-Spy:W32/Chymine.A) from a remote site:

• http://205.209.171.[...]/bin.exe

To a temporary file. During execution, the malware creates a file on the system, where the downloaded bin.exe file drops a DLL file, the actual keylogger component. In the sample we analyzed, the created file was:

• %windir%\system32\[5250].dll

The file name, in this instance [5250], may be a random number. This DLL component (and its file) is also detected as Trojan-Spy:W32/Chymine.A.

Registry

In order to run, the keyloggger component makes changes to a number of registry keys and injects code into a number of processes. The malware also creates the following launchpoints, which are involved in launching the keylogger component:

• HKLM\SYSTEM\CurrentControlSet\Services\Iprip\Parameters ServiceDll = .\5250~1\ by %windir%\system32\rundll32.exe [Launchpoint: ServiceDll]
• HKLM\System\CurrentControlSet\Services\Iprip ImagePath = %SystemRoot%\system32\svchost.exe -k netsvcs by %windir%\system32\services.exe [Launchpoint: Service]