RANSOM_CRYPACP.B

September 11, 2015

Analysis by: Anthony Joe Melgarejo

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:

788,480 bytes

File Type:

EXE

Initial Samples Received Date:

30 Aug 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:

%All Users Profile%\Desktop\how to decrypt files.lnk
%System Root%\{random numbers}\lsass86vl.exe
%System Root%\{random numbers}\howtodecryptaesfiles.htm
%System Root%\{random numbers}\howtodecryptaesfiles2.htm
%System Root%\{random numbers}\{random numbers}.list
%System Root%\ProgramData\svtstcrs\stplsctkvbs.dll
%System Root%\ProgramData\svcfnmainstvestvs\stppthmainfv.dll
%System Root%\ProgramData\svcfnmainstvestvs\xerrors.txt
%System Root%\ProgramData\{random numbers 1}\svchost.exe
%System Root%\ProgramData\{random numbers 2}\svchost.exe
%System Root%\ProgramData\{random numbers 3}\{random numbers}.bat
%System Root%\ProgramData\{random numbers 3}\{random numbers}.txt
%System Root%\ProgramData\{random numbers 3}\{random numbers}.dlls
%System Root%\ProgramData\{random numbers 4}\{random numbers}.dll
%System Root%\ProgramData\{random numbers 4}\{random numbers}fspall1.dll
%System Root%\ProgramData\{random numbers 4}\BKR{random numbers}.dll
%System Root%\ProgramData\{random numbers 4}\BKR2{random numbers}.dll
%System Root%\ProgramData\{random numbers 4}\BDR{random numbers}.dll
%System%\{random numbers}.dll
%System%\default2.sfx
%System%\decryptaesfiles.htm
%System%\btlogoffusrsmtv.bat
%System%\wblsys32vt86exkdll.dll
%System Root%\{random numbers}\svchost.exe

(Note: %All Users Profile% is the All Users folder, where it usually is C:\Documents and Settings\All Users on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData 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 Root% is the Windows root folder, where it usually is C:\ on all Windows operating system versions.. %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

It creates the following folders:

%System Root%\{random numbers}
%System Root%\ProgramData\svcfnmainstvestvs
%System Root%\ProgramData\svtstcrs
%System Root%\ProgramData\{random numbers 1}
%System Root%\ProgramData\{random numbers 2}
%System Root%\ProgramData\{random numbers 3}
%System Root%\ProgramData\{random numbers 4}

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

Autostart Technique

This Trojan registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\WinSamSs
ImagePath = {malware file path}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\WinSamSs
DisplayName = "Windows Security Accounts Manager"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\WinSamSs
Description = "The startup of this service signals to other services that the Security Accounts Manager (SAM) is ready to accept other requests. Disabling this service will prevent other services in the system from being notified when the SAM is ready, which may in turn cause those services to fail to start correctly. This service should not be disabled."

It creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
%System Root%\{random numbers}\howtodecryptaesfiles = %System Root%\{random numbers}\howtodecryptaesfiles.htm

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\WinSamSs

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
PCHealth\ErrorReporting
ForceQueueMode = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
PCHealth\ErrorReporting
IncludeShutdownErrs = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\Windows Error Reporting
Disabled = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\Windows Error Reporting
DisableArchive = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\Windows Error Reporting
DisableQueue = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\Windows Error Reporting
DontSendAdditionalData = "1"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\Windows Error Reporting
ForceQueue = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\Windows Error Reporting
LoggingDisabled = "1"

It modifies the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
PCHealth\ErrorReporting
IncludeMicrosoftApps = "0"