PE_CAOLYWA.A-O

 Analysis by: Mark Joseph Manahan

 ALIASES:

Worm:Win32/Otwycal.gen!A (Microsoft), Worm.Win32.Otwycal.c (Kaspersky), W32.SillyDC (Symantec)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: File infector

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Downloaded from the Internet, Via removable drives, Infects files


This file infector arrives via removable drives. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites. It may be dropped by other malware.

It infects by appending its code to target host files. It infects certain file types by inserting code in the said files. It creates an infection marker in infected files.

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size:

14,680 bytes

File Type:

EXE

File Compression:

WinUpack

Memory Resident:

Yes

Initial Samples Received Date:

08 Apr 2009

Payload:

Compromises system security, Terminates processes, Downloads files

Arrival Details

This file infector arrives via removable drives.

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

It may be dropped by the following malware:

  • PE_CAOLYWA.A

Installation

This file infector drops the following copies of itself into the affected system:

  • %Windows%\Tasks\0x01xx8p.exe

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

It drops the following files:

  • {drive letter}:\MSDOS.bat
  • c:\zzz.sys

It drops the following non-malicious files:

  • %Windows%\Tasks\explorer.ext (backup of explorer.exe)
  • %Windows%\Tasks\SysFile.brk (backup of explorer.exe)

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

File Infection

This file infector infects the following file types:

  • .exe
  • .cmd
  • .bat
  • .com
  • .scr

It infects by appending its code to target host files.

It infects files with the following file extensions by inserting code in the said files:

  • .do
  • .htm
  • .html
  • .shtm
  • .shtml
  • .asp
  • .aspx
  • .php
  • .jsp
  • .cgi
  • .xml
  • .GHO

It creates an infection marker in infected files.

It avoids infecting folders containing the following strings:

  • Program Files

It avoids infecting the following files:

  • qq.exe
  • QQDoctor.exe
  • QQDoctorMain.exe

Propagation

This file infector drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[AutoRun]
open=MSDOS.bat
shell\open={characters}
shell\open\Command=MSDOS.bat
shell\open\Default=1
shell\explore={characters}
shell\explore\Command=MSDOS.bat

Backdoor Routine

This file infector executes the following commands from a remote malicious user:

  • Visit URL(s)
  • Download and execute files
  • Infect files
  • Spread via removable drives

Process Termination

This file infector terminates the following processes if found running in the affected system's memory:

  • avp.exe
  • kvsrvxp.exe
  • kissvc.exe

Download Routine

This file infector saves the files it downloads using the following names:

  • %System%\windows.txt

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

Information Theft

This file infector accesses the following site to download its configuration file:

  • http://c.{BLOCKED}m.com/config.txt

  SOLUTION

Minimum Scan Engine:

9.300

VSAPI OPR PATTERN File:

5.955.00

VSAPI OPR PATTERN Date:

09 Apr 2009

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Remove the malware/grayware file that dropped/downloaded PE_CAOLYWA.A-O

     PE_CAOLYWA.A

Step 3

Search and delete AUTORUN.INF files created by PE_CAOLYWA.A-O that contain these strings

[ Learn More ]
  • [AutoRun]
  • open=MSDOS.bat
  • shell\open={characters}
  • shell\open\Command=MSDOS.bat
  • shell\open\Default=1
  • shell\explore={characters}
  • shell\explore\Command=MSDOS.bat

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

Search and delete these files

[ Learn More ]
There may be some component 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.
  • %Windows%\Tasks\spoolsv.ext
  • %Windows%\Tasks\SysFile.brk
  • %System%\windows.txt
  • {drive letter}:\MSDOS.bat
  • c:\zzz.sys

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as PE_CAOLYWA.A-O. 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.


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