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BKDR_CAPHAW.G

September 21, 2013
 Analysis by: Anthony Joe Melgarejo
 ALIASES:

W32/Caphaw.I (Fortinet), Win32/Caphaw.I trojan (ESET)

 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:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware


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.

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

It steals certain information from the system and/or the user.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

385,024 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

19 Sep 2013

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 injects codes into the following process(es):

  • explorer.exe

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{random}.exe = "%Application Data%\{random folder found}\{filename found in %System%}"

Other System Modifications

This backdoor adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Internet Explorer\Main
NoProtectedModeBanner = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings
DisableCachingOfSSLPages = "1"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings\
Zones\3
2500 = "3"

It modifies the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Internet Settings\
Zones\3
1609 = "3"

(Note: The default value data of the said registry entry is 1.)

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • Download and execute arbitrary files
  • Upload files
  • Update itself
  • Modify system settings
  • Terminate processes

Information Theft

This backdoor steals the following information:

  • CPU Information
  • OS Version and Installation Information
  • Disk Devices list, type and status
  • Computer Name
  • Admin Rights
  • Code Page
  • Web Browser Version (Internet Explorer, Firefox, Chrome)
  • Anti-malware Software Installed
  • Virtual Machine check
  • Startup Programs
  • VMWare Information
  • Installed Software (found under HKEY_LOCAL_MACHINE\SOFTWARE registry subkey)
  • Running Processes
  • Cookies
  • Network traffic

Other Details

This backdoor deletes the initially executed copy of itself

NOTES:
This backdoor drops a copy of itself in random legitimate folders or subfolders found in the %Application Data% folder. It uses the file name of a file found in the %System% folder (e.g., %Application Data%\Microsoft\CryptnetUrlCache\Content\runas.exe).

It generates random subdomains for the following C&C servers. ({random subdomain}.{C&C server}.su:443/ping.html)

  • https://{BLOCKED}oo.su/ping.html
  • https://{BLOCKED}gh.su/ping.html
  • https://{BLOCKED}5ja.cc/ping.html

If a connection to a C&C server is successful, it may download its components/configuration may contain information like targeted online banking sites.

  SOLUTION

Minimum Scan Engine:

9.300

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
    • {random}.exe = "%Application Data%\{random folder found}\{filename found in %System%}"
  • In HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main
    • NoProtectedModeBanner = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings
    • DisableCachingOfSSLPages = "1"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3
    • 2500 = "3"

Step 4

Restore this modified 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\Internet Settings\Zones\3
    • From: 1609 = "3"
      To: 1609 = 1

Step 5

Restart in normal mode and scan your computer with your Trend Micro product for files detected as BKDR_CAPHAW.G. 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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