RANSOM_CRYPFINI.A

December 05, 2015
 Analysis by: Anthony Joe Melgarejo
 ALIASES:

Ransom:Win32/Finicrypt.A (Microsoft)

 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.

  TECHNICAL DETAILS

File Size:

496,128 bytes

File Type:

EXE

Initial Samples Received Date:

17 Nov 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 drops the following files:

  • ReadDecryptFilesHere.txt - to all folders with encrypted files

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

  • %User Profile%\{Computer Name}{Volume Serial Number}.exe

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

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
Microsoft Corporation = "%User Profile%\{Computer Name}{Volume Serial Number}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\CryptInfinite

HKEY_CURRENT_USER\Software\CryptInfinite\
Info

HKEY_CURRENT_USER\Software\CryptInfinite\
Files

It adds the following registry entries:

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
KEYFREE = "{10 random characters}"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
KEY = "{70 random characters}"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
KEYFREE = "{10 random characters}"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
1 = "000000"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
c = "23"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
m = "59"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
s = "59"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
FreeFile = "{file name of 10th encrypted file}"

HKEY_CURRENT_USER\Software\CryptInfinite\
Info
Finish = "True"

HKEY_CURRENT_USER\Software\CryptInfinite\
Files
{number starting from 1 until number of encrypted files (multiple entries)} = "{file name of encrypted file}"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://{BLOCKED}6k7iivyki2.onion.direct/lending/bot.php

It renames encrypted files using the following names:

  • {original file name and extension}.crinf