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BKDR_CAPHAW.LEK

September 01, 2018
 Analysis by: Michael Jhon Ofiaza
 ALIASES:

Backdoor:Win32/Caphaw.D (Microsoft)

 PLATFORM:

Windows

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

  • 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.

However, as of this writing, the said sites are inaccessible. It deletes itself after execution.

  TECHNICAL DETAILS

File Size:

249,856 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

23 Oct 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 drops the following copies of itself into the affected system:

  • %Application Data%\{random folder found}\{filename found in %System%}

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

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 base64 chars} = "%Application Data%\{random folder found}\{filename found in %System%}"

Other System Modifications

This Backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Multimedia\Audio Compression Manager

HKEY_CURRENT_USER\Software\Microsoft\
Multimedia\Audio Compression Manager\MSACM

HKEY_CURRENT_USER\Software\Microsoft\
Multimedia\Audio Compression Manager\Priority v4.00

It adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.imaadpcm
fdwSupport = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.imaadpcm
cFormatTags = 2

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.imaadpcm
aFormatTagCache = {Value}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.imaadpcm
cFilterTags = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msg711
fdwSupport = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msg711
cFormatTags = 3

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msg711
aFormatTagCache = {value}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msg711
cFilterTags = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msgsm610
fdwSupport = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msgsm610
cFormatTags = 2

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msgsm610
aFormatTagCache = {value}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msgsm610
cFilterTags = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msadpcm
fdwSupport = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msadpcm
cFormatTags = 2

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msadpcm
aFormatTagCache = {value}

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.msadpcm
cFilterTags = 0

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.l3acm
fdwSupport = 1

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.l3acm
cFormatTags = 2

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
AudioCompressionManager\DriverCache\msacm.l3acm
aFormatTagCache = {value}

Other Details

This Backdoor connects to the following possibly malicious URL:

  • It uses domain generation algorithm (DGA) for its C&C servers. Where the domain could be one of the following:
    • http://eoz5u{BLOCKED}mc6r0f.fey.su:443
    • http://yv4lfo{BLOCKED}c.exy.su:443
    • http://tvlobc{BLOCKED}.enp.cc:443

However, as of this writing, the said sites are inaccessible.

It deletes itself after execution.

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.478.01

FIRST VSAPI PATTERN DATE:

31 Aug 2018

VSAPI OPR PATTERN File:

14.479.00

VSAPI OPR PATTERN Date:

01 Sep 2018

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {random base64 chars} = "%Application Data%\{random folder found}\{filename found in %System%}"

Step 5

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
    • AudioCompressionManager
  • In HKEY_CURRENT_USER\Software\Microsoft\Multimedia
    • Audio Compression Manager

Step 6

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