TROJ_ENCPDF.A

 Analysis by: kathleenno

 ALIASES:

Troj/EncPdf-A (Sophos); W32/EncPdf.A!tr (Fortinet)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • 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:

685,568 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

08 Apr 2011

Payload:

Modifies HOSTS file, Drops files

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:

  • %System%\mstap32.exe - also detected as TROJ_ENCPDF.A
  • %System%\htdns.dll - non-malicious file
  • %User Temp%\GeoIP.dat - non-malicious file
  • %Windows%\pdoor.exe - non-malicious file

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.. %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.. %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

Autostart Technique

This Trojan modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = %System%\userinit.exe,%System%\mstap32.exe

(Note: The default value data of the said registry entry is %System%\userinit.exe,.)

Other System Modifications

This Trojan adds the following registry entries:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLUA = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0002
EnableForRas = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0002
EnableForRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0002
EnableForOutboundRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0003
EnableForRas = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0003
EnableForRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0003
EnableForOutboundRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0004
EnableForRas = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0004
EnableForRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0004
EnableForOutboundRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0005
EnableForRas = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0005
EnableForRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\
0005
EnableForOutboundRouting = 0

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasMan\Parameters
IpOutLowWatermark = 1

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasMan\Parameters
IpOutHighWatermark = 5

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasMan\Parameters
NbfOutLowWatermark = 1

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasMan\Parameters
NbfOutHighWatermark = 5

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasMan\Parameters
NbfInLowWatermark = 1

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\RasMan\Parameters
NbfInHighWatermark = 5

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

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\BAP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\PPP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASBACP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASCCP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASEAP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASIPCP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASIPHLP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASMAN

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASPAP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASQEC

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASSPAP

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Tracing\RASTAPI

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\Eventlog\Application\
Microsoft H.323 Telephony Service Provider

HOSTS File Modification

This Trojan adds the following strings to the Windows HOSTS file:

  • 69.90.81.66 {username}

  SOLUTION

Minimum Scan Engine:

8.900

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\system
    • EnableLUA = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0002
    • EnableForRas = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0002
    • EnableForRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0002
    • EnableForOutboundRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0003
    • EnableForRas = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0003
    • EnableForRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0003
    • EnableForOutboundRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0004
    • EnableForRas = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0004
    • EnableForRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0004
    • EnableForOutboundRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0005
    • EnableForRas = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0005
    • EnableForRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002bE10318}\0005
    • EnableForOutboundRouting = 0
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\Parameters
    • IpOutLowWatermark = 1
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\Parameters
    • IpOutHighWatermark = 5
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\Parameters
    • NbfOutLowWatermark = 1
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\Parameters
    • NbfOutHighWatermark = 5
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\Parameters
    • NbfInLowWatermark = 1
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\RasMan\Parameters
    • NbfInHighWatermark = 5

Step 4

Delete this registry key

[ 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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • BAP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • PPP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASBACP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASCCP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASEAP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASIPCP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASIPHLP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASMAN
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASPAP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASQEC
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASSPAP
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Tracing
    • RASTAPI
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Eventlog\Application
    • Microsoft H.323 Telephony Service Provider

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 NT\CurrentVersion\Winlogon
    • From: Userinit = %System%\userinit.exe,%System%\mstap32.exe
      To: %System%\userinit.exe,

Step 6

Remove these strings added by the malware/grayware/spyware in the HOSTS file

[ Learn More ]
    69.90.81.66 {username}
"

Step 7

Search and delete this file

[ Learn More ]
There may be some component 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%\htdns.dll
%User Temp%\GeoIP.dat
%Windows%\pdoor.exe

Step 8

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