WORM_COREFLOOD.A

Upon execution, it terminates EXPLORER.EXE and restarts the process with its code injected in it. It then attempts to resolve the host to any certain servers. Once a user opens a browser, it will perform a HTTP POST request containing system information. It expects to receive backdoor commands from the server. The server replies with certain commands such as to download, execute, and save the downloaded copy of itself.

It scans the network for random IP addresses to search for target systems. It then attempts to drop and execute the copy of itself to target IP addresses.

It downloads a non-malicious component from its server. It then uses this downloaded file to unpack the archive file it downloads from the server. The said archive file contains an updated copy of this worm.

It monitors certain applications. It logs user keystrokes when affected users visit websites. It logs the status of its installation to the affected system and to all the network shares it tried to infect to certain files. It may also steal data from HTTPS sessions.

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

Arrival Details

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

It may be downloaded from the following remote sites:

• http://savupdate.{BLOCKED}evalidate.net/ctfup32.rar
• http://health.{BLOCKED}plus.net/ctfup32.rar

Installation

This worm drops the following files:

• %User Temp%\~~{random number}.tmp - also detected as BKDR_OFICLA.AI
• %System%\{random file name}.dat - encrypted data
• %System%\{random file name}.ocx - copy of itself

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.. %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

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

HKEY_CLASSES_ROOT\CLSID\{random CLSID}
(Default) = {random registry value}

HKEY_CLASSES_ROOT\CLSID\{random CLSID}\
InprocServer32
(Default) = %System%\{random file name}.ocx

HKEY_CLASSES_ROOT\CLSID\{random CLSID}\
InprocServer32
ThreadingModel = Apartment

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
ShellIconOverlayIdentifiers\{random key}
(Default) = {random CLSID}

Other Details

Based on analysis of the codes, it has the following capabilities:

• Backdoor Routines

  Upon execution, it terminates EXPLORER.EXE and restarts the process with its code injected in it. It then attempts to resolve the host to any of the following servers:

  • http://{BLOCKED}ate.licensevalidate.net
  • http://{BLOCKED}s.hostfarmville.net

  Once a user opens a browser, it will perform a HTTP POST request with the following parameters containing system information:

  • http://{malware server}/index.php/r={parameter}&i=&v={version}&os={operating system}&s=&h=&d={parameter}&b={parameter}&u={parameter}&k={parameter}&m={parameter}&panic={parameter}&ie={parameter}&input={parameter}&c={country of affected system}&l={parameter}

  It will then expect to receive backdoor commands from the server.

  As of writing, the server replies with commands that does the following:

  • Assign a unique ID for the bot
  • Move a file named "c:\myservice.log" - not present in the system
  • Download, execute, and save the file downloaded from the website http://savupdate.{BLOCKED}evalidate.net/login.php as %User Temp%\tmsfoload.exe. Trend Micro detects this executable file as WORM_COREFLOOD.A. As of writing, the downloaded file is an updated copy of itself.

• Propagation via Network Shares

  • It scans the network for random IP addresses to search for target systems.
  • It then attempts to drop and execute the following copy of itself to target IP addresses:
  • %Windows%\System\ctfmnt.exe

• Download Routine

  It downloads a non-malicious component file named rar.exe from its server. It will then use this downloaded file to unpack the next file it will download from the server, ctfup32.rar, which is an archive file containing an updated copy of the malware.

  Initially, the malware will save all the downloaded files to the %User Temp% folder. Afterwards, it will install the contents of the archive ctfup32.rar to the %Windows%\System folder.

• Information Theft

  It monitors certain applications such as the following:

  • Firefox
  • Opera
  • Skype

  It logs user keystrokes when affected users visit Web sites with the following strings:

  • answer
  • challenge
  • clave
  • codigo
  • firma
  • identifica
  • memorable
  • parol
  • passphras
  • password
  • secret
  • secur
  • segur

• Other Details

• It logs the status of its installation to the affected system and to all the network shares it tried to infect to the following files:
• %User Temp%\tlmlg1.log
• %User Temp%\tlmlg2.log
• It uploads the file %User Temp%\cmtemp.tmp to its server.
• It may also perform the following:
  • Steal data from HTTPS sessions.
  • Read these component files, which are currently not found on systems: ie.dat, input.dat, other.dat, panic.dat.