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WORM_SLENBOT.AB

January 28, 2015
 Analysis by: Michael John Marcos
 ALIASES:

a variant of Win32/Kryptik.SYB (Eset), Trojan.Win32.Genome.aabbm (Kaspersky), Win32.SuspectCrc (Ikarus), W32/Dx.BAGU!tr (Fortinet)

 PLATFORM:

Windows

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Propagates via software vulnerabilities

This worm may be unknowingly downloaded by a user while visiting malicious websites.

It exploits software vulnerabilities to propagate to other computers across a network.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

34,304 bytes

File Type:

EXE

Initial Samples Received Date:

19 Aug 2011

Payload:

Connects to URLs/IPs

Arrival Details

This worm may be unknowingly downloaded by a user while visiting malicious websites.

Installation

This worm drops the following files:

  • \.\rotcetorp
  • %User Profile%\userdiff.sav
  • %System%\userdiff.sav

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It drops the following copies of itself into the affected system:

  • %User Profile%\{random filename}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
MSConfig = "%User Profile%\{random filename}.exe \u"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe"

Propagation

This worm exploits the following software vulnerabilities to propagate to other computers across a network:

Download Routine

This worm connects to the following URL(s) to download its component file(s):

  • http://ypql.{BLOCKED}ackupsvc.su/sys/ybsk2.txt

Other Details

This worm deletes the initially executed copy of itself

NOTES:
It propagates in the network as instructed by the remote malicious user.

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

8.366.17

FIRST VSAPI PATTERN DATE:

19 Aug 2011

VSAPI OPR PATTERN File:

8.367.00

VSAPI OPR PATTERN Date:

19 Aug 2011

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 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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • MSConfig = "%User Profile%\{random filename}.exe \u"

Step 4

Search and delete this file

[ Learn More ]
There may be some files 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.  
  • \.\rotcetorp
  • %User Profile%\userdiff.sav
  • %System%\userdiff.sav
  • %User Profile%\{random filename}.exe

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_SLENBOT.AB. 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 6

Download and apply this security patch Refrain from using these products until the appropriate patches have been installed. Trend Micro advises users to download critical patches upon release by vendors.


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