TROJ_CRYPTODEF.C
Ransom:Win32/Crowti (Microsoft); Trojan.Cryptodefense (Symantec); Trojan-Ransom.Win32.Cryptodef.vsd (Kaspersky); Mal/Generic-L (Sophos); Trojan.Win32.Generic!BT (Sunbelt); Trojan horse Inject2.CKTJ (AVG)
Windows
![](/vinfo/imgFiles/legend.jpg)
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 itself after execution.
TECHNICAL DETAILS
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 drops the following copies of itself into the affected system:
- %System Root%\{Random 8 Characters}\{Random 8 Characters}.exe
- %Application Data%\{Random 8 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
{First 7 Characters of {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
{Second to the Sixth Characters {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\RunOnce
{Last Seven Characters of {Random 8 Characters}} = "%Application Data%\{Random 8 Characters}.exe"
HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
{Random 8 Characters} = "%Application Data%\{Random 8 Characters}.exe"
It drops the following file(s) in the Windows Startup folder to enable its automatic execution at every system startup:
- %User Startup%\{Random 8 Characters}.exe
(Note: %User Startup% is the current user's Startup folder, which is usually C:\Documents and Settings\{user}\Start Menu\Programs\Startup on Windows 2000 and XP, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup on Windows Vista, 7, and 8.)
Other System Modifications
This Trojan adds the following registry keys:
HKEY_CURRENT_USER\Software\{random string}
It adds the following registry entries:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SystemRestore
DisableSR = "1"
Other Details
This Trojan connects to the following possibly malicious URL:
- http://{BLOCKED}r.es
- http://matheusprado.{BLOCKED}m.br
- {BLOCKED}5.164.184
- {BLOCKED}5.209.102
- {BLOCKED}8.47.225
- {BLOCKED}5.17.12
It deletes itself after execution.
NOTES:
This Trojan is capable of encrypting files in the affected system.
It drops HELP_DECRYPT.HTML, HELP_DECRYPT.PNG, HELP_DECRYPT.TXT, and HELP_DECRYPT.URL to all folders where files are encrypted.
SOLUTION
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
Step 3
Delete this registry key
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
- {random string} = ""
- {random string} = ""
Step 4
Delete this registry value
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 8 Characters} = "%Application Data%\{Random 8 Characters}.exe"
- {Random 8 Characters} = "%Application Data%\{Random 8 Characters}.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
- {First 7 Characters of {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
- {First 7 Characters of {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
- {Second to the Sixth Characters {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
- {Second to the Sixth Characters {Random 8 Characters}} = "%System Root%\{Random 8 Characters}\{Random 8 Characters}.exe"
- In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce
- {Last Seven Characters of {Random 8 Characters}} = "%Application Data%\{Random 8 Characters}.exe"
- {Last Seven Characters of {Random 8 Characters}} = "%Application Data%\{Random 8 Characters}.exe"
- In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SystemRestore
- DisableSR = "1"
- DisableSR = "1"
Step 5
Search and delete this file
*Note: The file name input box title varies depending on the Windows version (e.g. Search for files or folders named or All or part of the file name.).
• For Windows Vista, Windows 7, Windows Server 2008, Windows 8, Windows 8.1, and Windows Server 2012:
- Open a Windows Explorer window.
- For Windows Vista, 7, and Server 2008 users, click Start>Computer.
- For Windows 8, 8.1, and Server 2012 users, right-click on the lower left corner of the screen, then click File Explorer.
- In the Search Computer/This PC input box, type:
DATA_GENERIC - Once located, select the file then press SHIFT+DELETE to delete it.
*Note: Read the following Microsoft page if these steps do not work on Windows 7.
Step 6
Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_CRYPTODEF.C. 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.
Did this description help? Tell us how we did.