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BKDR_REMCOS.TICOGBF

May 29, 2018
 Analysis by: John Donnie Celestre
 ALIASES:

Exploit.Win32.BypassUAC.lmq (KASPERSKY), W32/Kryptik.GEAB!tr (FORTINET)

 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.

  TECHNICAL DETAILS

File Size:

337,240 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

23 May 2018

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 a copy of itself in the following folders using different file names:

  • %Application Data%\Microsoft\csrss.exe (w/ no admin rights)
  • %System%\Microsoft\csrss.exe (w/ admin rights)

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It drops the following files:

  • %Application Data%\remcos\logs.dat

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

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
csrss = "%Application Data%\Microsoft\csrss.exe" (w/ no admin rights)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
csrss = "%Application Data%\Microsoft\csrss.exe" (w/ no admin rights)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
csrss = "%System%\Microsoft\csrss.exe" (w/ admin rights)

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
csrss = "%System%\Microsoft\csrss.exe" (w/ admin rights)

Other System Modifications

This Backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\Qt01lk2A-M2MXUN

It adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\Qt01lk2A-M2MXUN
EXEpath = {hex data}

It modifies the following registry keys:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Policies\
System
EnableLUA = 0

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

Other Details

This Backdoor connects to the following possibly malicious URL:

  • http://1.{BLOCKED}i.club
  • http://{BLOCKED}.{BLOCKED}.106.2

  SOLUTION

Minimum Scan Engine:

9.850

FIRST VSAPI PATTERN FILE:

14.268.05

FIRST VSAPI PATTERN DATE:

23 May 2018

VSAPI OPR PATTERN File:

14.269.00

VSAPI OPR PATTERN Date:

24 May 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
    • csrss = "%System%\Microsoft\csrss.exe"   (w/ admin rights)
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • csrss = "%Application Data%\Microsoft\csrss.exe"   (w/ no admin rights)
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • csrss = "%System%\Microsoft\csrss.exe"   (w/ admin rights)
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • csrss = "%Application Data%\Microsoft\csrss.exe"   (w/ no admin rights)

Step 5

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
    • From: EnableLUA = "0"
      To: EnableLUA = 1

Step 6

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.
  • %System%\Microsoft\csrss.exe   (w/ admin rights)
  • %Application Data%\Microsoft\csrss.exe   (w/ no admin rights)
  • %Application Data%\remcos\logs.dat

Step 7

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