ALIASES:

Backdoor:Win32/Subseven.2_2, Backdoor:Win32/Litmus.AB (Microsoft); BackDoor-Sub7.svr (McAfee); Backdoor.Litmus.203 (Symantec); PAK:UPX, Backdoor.Win32.SubSeven.22.a (Kaspersky); Trojan.Win32.Ircbot!cobra (v) (Sunbelt)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size: 106,211 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 15 Oct 2012

Arrival Details

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This backdoor drops the following copies of itself into the affected system:

  • %System%\diyihkx.exe
  • %System Root%\EXPLORER.EXE
  • %System%\apka.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

It creates the following folders:

  • %Windows%\litmus

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
RunDLL30 = "%System%\diyihkx.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Active Setup\Installed Components\apka
StubPath = "%System%\apka.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
LTM2 = "%Windows%\litmus\ha.exe"

Other System Modifications

This backdoor modifies the following file(s):

  • %System%\drivers\etc\services

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

It adds the following registry keys:

HKEY_LOCAL_MACHINE\Software\Microsoft\
Active Setup\Installed Components\apka

HKEY_LOCAL_MACHINE\Software\Microsoft\
ENC

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
 ¸â¼¦¨ = "~vœœd"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
§ßæ˜ = "²¸Ù"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
 ¸âº¡™ = "²¸Ù"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
 ¸â¼¦£ = "²¸ÙÍ"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
™µÏ²¢ = "°€ÈÐgj¢¡{ƒÐ¬–i„„«¢8¨£Ñšl¢£ª„£{g™}‚§£2°~¤Òl“ÒÎx~Ÿªli‚†xÐ0ªŸ¢˜–Î¥©}¤«hi…€«Ò5"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
œ´Ï¯£¢ = "{random characters}"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
 ºÞ¹¨˜ = "~wee¾»»°’€g}"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
ENC
™µÏ²¢ = "€ÈÃ}‚°» È¹­§Á²³Ÿ2©ªÕ坜×ät²ä«"

Dropping Routine

This backdoor drops the following files:

  • temp.exe
  • %Windows%\litmus\ha.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows.)

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine: 9.200

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Active Setup\Installed Components
    • apka
  • In HKEY_LOCAL_MACHINE\Software\Microsoft
    • ENC

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • RunDLL30 = "%System%\diyihkx.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Active Setup\Installed Components\apka
    • StubPath = "%System%\apka.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • LTM2 = "%Windows%\litmus\ha.exe"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    •  ¸â¼¦¨ = "~vœœd"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    • §ßæ˜ = "²¸Ù"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    •  ¸âº¡™ = "²¸Ù"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    •  ¸â¼¦£ = "²¸ÙÍ"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    • ™µÏ²¢ = "°€ÈÐgj¢¡{ƒÐ¬–i„„«¢8¨£Ñšl¢£ª„£{g™}‚§£2°~¤Òl“ÒÎx~Ÿªli‚†xÐ0ªŸ¢˜–Î¥©}¤«hi…€«Ò5"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    • œ´Ï¯£¢ = "{random characters}"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    •  ºÞ¹¨˜ = "~wee¾»»°’€g}"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ENC
    • ™µÏ²¢ = "€ÈÃ}‚°» È¹­§Á²³Ÿ2©ªÕ坜×ät²ä«"

Step 5

Search and delete these components

[ Learn More ]
There may be some components that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • temp.exe
  • %Windows%\litmus\ha.exe

Step 6

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Windows%\litmus

Step 7

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_SUB7.22A. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.

Step 8

Restore deleted/modified files and/or registry entries from backup

*Note: Only Microsoft-related files/keys/values will be restored. If this malware/grayware also deleted registry keys/values related to programs that are not from Microsoft, please reinstall those programs on your computer.

    • %System%\drivers\etc\services


Did this description help? Tell us how we did.