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TROJ_CRYPDEF.AA

March 24, 2015
 ALIASES:

Trojan-Ransom.Win32.Blocker.grqn (Kaspersky)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

286,720 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

19 Mar 2015

Arrival Details

This Trojan 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 Trojan adds the following folders:

  • %System Root%\{8 alphanumeric characters}

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

It drops the following files:

  • HELP_DECRYPT.HTML
  • HELP_DECRYPT.PNG
  • HELP_DECRYPT.TXT
  • HELP_DECRYPT.URL

It drops the following copies of itself into the affected system:

  • %System Root%\{8 alphanumeric characters}\{8 alphanumeric characters}.exe
  • %Application Data%\{8 alphanumeric characters}.exe

(Note: %System Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %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 Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{7 alphanumeric characters} = "%System Root%\{8 alphanumeric characters}\{8 alphanumeric characters}.exe"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{8 alphanumeric characters} = "%Application Data%\{8 alphanumeric characters}.exe"

It enables its automatic execution at every system startup by dropping the following copies of itself into the Windows Common Startup folder:

  • %User Startup%\{8 alphanumeric characters}.exe

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

Other System Modifications

This Trojan modifies the following file(s):

  • database files
  • web files
  • MS Office files
  • video
  • images
  • script files
  • text files
  • other non-binary files

It adds the following registry keys:

HKEY_CURRENT_USER\Software\{32 alphanumeric characters}

HKEY_CURRENT_USER\Software\{32 alphanumeric characters}\
{16 alphanumeric characters}

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\BITS
Start = "4"

(Note: The default value data of the said registry entry is "3".)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\ERSvc
Start = "4"

(Note: The default value data of the said registry entry is "2".)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wscsvc
Start = "4"

(Note: The default value data of the said registry entry is "2".)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\wuauserv
Start = "4"

(Note: The default value data of the said registry entry is "2".)

Other Details

This Trojan connects to the following URL(s) to get the affected system's IP address:

  • http://ip-addr.es/

It connects to the following possibly malicious URL:

  • http://{BLOCKED}ook.net/img1.php?{letter}={random}
  • http://{BLOCKED}lyblocks.com/404.php
  • http://{BLOCKED}lyblocks.com/img4.php?{letter}={random}
  • http://{BLOCKED}rdening.com/img3.php?{letter}={random}
  • http://{BLOCKED}and-charm.com/img3.php?{letter}={random}
  • http://{BLOCKED}c.net/img3.php?{letter}={random}
  • http://{BLOCKED}and-charm.com/img3.php?{letter}={random}

It deletes the initially executed copy of itself

  SOLUTION

Minimum Scan Engine:

9.750

FIRST VSAPI PATTERN FILE:

11.548.04

FIRST VSAPI PATTERN DATE:

19 Mar 2015

VSAPI OPR PATTERN File:

11.549.00

VSAPI OPR PATTERN Date:

20 Mar 2015

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

Scan your computer with your Trend Micro product and note files detected as TROJ_CRYPDEF.AA

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

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
    • {7 alphanumeric characters} = "%System Root%\{8 alphanumeric characters}\{8 alphanumeric characters}.exe"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • {8 alphanumeric characters} = "%Application Data%\{8 alphanumeric characters}.exe"

Step 6

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\SYSTEM\CurrentControlSet\Services\BITS
    • From: Start = "4"
      To: Start = "3"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ERSvc
    • From: Start = "4"
      To: Start = "2"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wscsvc
    • From: Start = "4"
      To: Start = "2"
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wuauserv
    • From: Start = "4"
      To: Start = "2"

Step 7

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %System Root%\{8 alphanumeric characters}

Step 8

Search and delete these files

[ 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.
  • HELP_DECRYPT.HTML
  • HELP_DECRYPT.PNG
  • HELP_DECRYPT.TXT
  • HELP_DECRYPT.URL

Step 9

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

Step 10

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • database files
  • web files
  • MS Office files
  • video
  • images
  • script files
  • text files
  • other non-binary files

Step 11

The following created files/folders/registry keys/registry entries cannot be identified by the user since there are no reference values in the created key. The only way it can be identified is by comparing the present system information with a backup. Note that the said components do not have to be deleted since it won't be harmful to the system.

  • In HKEY_CURRENT_USER\Software
    • {32 alphanumeric characters}
  • In HKEY_CURRENT_USER\Software\{32 alphanumeric characters}
    • {16 alphanumeric characters}


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