Threat Descriptions

Trojan:W32/Lethic

Classification

Category :

Malware

Type :

Trojan

Platform :

W32

Aliases :

Trojan.TR/Crypt.XPACK.[variant]

Summary

Lethic is a spambot that constantly connects to a remote server and may download additional malware into the system it infected. It utilizes process injection method to inject malicious code in explorer.exe and resume its malicious activities.

Removal

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    Note: If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note: You need administrative rights to change the settings.

Technical Details

Infection Vector

Lethic gain access into a system via attachments in spam emails.

Behavior

Upon execution, Lethic will first check for the presence of virtual and debugging environment. If found, it will proceed to terminate itself as a way to evade detection and analysis.

If no virtual or debugging environment found, it will proceed to add a registry key to gain persistence and then start locating the explorer.exe module for it to inject malicious code into. It will also add a mutual exclusion object (mutex) into the injected process to ensure that only one instance of itself is running.

Afterwards, it tries to connect to a malicious command and control (C&C) server using Winsock API and then waits for further instructions.

Files created

  • C:\RECYCLER\S-1-5-21-0243556031-888888379-781862338-196818750\backwindow32.exe

Registry Changes

Lethic adds the following registry keys to run during startup:

  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce

Name: backwindow32
Data: [dropped_path and filename].exe

Network activity

It connects to the following remote server:

  • hxxp://93.190[.]139.161:7700
  • It also connect to multiple IP addresses via TCP port 25.

Other Behavior

Lethic is capable of performing these tasks:

  • Check for virtual and debugging environment by checking the running process for:
    • Regmon.exe, filemon.exe, procdump.exe, procexp.exe, wireshark.exe, prcview.exe, sysinspector.exe, sniff_hit.exe, proc_watch.exe, apimonitor.exe, tcpview.exe, petools.exe, vmtoolsd.exe, autoruns.exe, vmusrvc.exe, vmsrvc.exe, xsvc_depriv.exe, xenservice.exe
  • Check if it is being debugged or sandboxed by checking if the following DLL file exist:
    • api_log.dll, log_api32.dll, dir_watch.dll, pstorec.dll, vmcheck.dll, wpespy.dll, snxhk.dll
  • Check the username for these matches:
    • MALTEST, TEQUILABOOMBOOM, SANDBOX, VIRUS, MALWARE
  • Check the filepath if it contains these items:
    • SAMPLE, MALWARE, SANDBOX, VIRUS
  • Check multiple registry keys for the following virtual environment:
    • QEMU, VMWARE, VBOX, BOCHS

Analysis on file: 7a60ae98b7707de05764d78d508dc3bc946d3108