TROJ_DLOADER.DNO

 Analysis by: Jaime Benigno Reyes

 ALIASES:

Downloader.Generic14.BKJ (AVG); Win32/TrojanDownloader.Hancitor.A (Nod32)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Via email, Downloaded from the Internet, Dropped by other malware

This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It executes then deletes itself afterward.

It does not have any propagation routine.

It does not have any backdoor routine.

It executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system. As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

77,824 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

26 Sep 2014

Payload:

Downloads files

Arrival Details

This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

It 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 and executes them:

  • %User Temp%\winlogin.exe

(Note: %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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It executes then deletes itself afterward.

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
winlogin = "%User Temp%\winlogin.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Active Setup\Installed Components\05F16C88-71D3-42C1-BB4F-E9BAF7DB4A9E

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

HKEY_CURRENT_USER\Software\Microsoft\
Active Setup\Installed Components\05F16C88-71D3-42C1-BB4F-E9BAF7DB4A9E
cfg = "{random}GRGRGRGR}{hostname} "

Propagation

This Trojan does not have any propagation routine.

Backdoor Routine

This Trojan does not have any backdoor routine.

Download Routine

This Trojan accesses the following websites to download files:

  • http://{BLOCKED}4qc2r4bn63.{BLOCKED}b.org:443
  • https://{BLOCKED}4qc2r4bn63.{BLOCKED}b.org/gate.php

It saves the files it downloads using the following names:

  • %User Temp%\___{random}.exe

(Note: %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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

As of this writing, the said sites are inaccessible.

Other Details

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

  • http://icanhazip.com:443

NOTES:

This Trojan connects to the following URLs to download and install a certificate so it could connect to the malicious site which is in a Tor2web proxy network:

  • http://www.download.windowsupdate.com/msdownload/update/v3/static/trustedr/en/authrootseq.txt
  • http://www.download.windowsupdate.com/msdownload/update/v3/static/trustedr/en/authrootstl.cab
  • http://www.download.windowsupdate.com/msdownload/update/v3/static/trustedr/en/B1BC968BD4F49D622AA89A81F2150152A41D829C.crt

The following registry key would be added after installing the certificate:

  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\B1BC968BD4F49D622AA89A81F2150152A41D829C

The following registry entry would be added after installing the certificate:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates\B1BC968BD4F49D622AA89A81F2150152A41D829C
Blob = {hex value}

The following files would be added after installing the certificate:

  • %Application Data%\Microsoft\Crypto\RSA\{User's Security Identifier}\{random 1} (Windows Vista and higher versions) - installing certificate
  • %Application Data%\Microsoft\Crypto\RSA\{User's Security Identifier}\{random 2} (Windows Vista and higher versions)
  • %Application Data%\Microsoft\CryptnetUrlCache\Content\{random 3} (Versions lower than Windows Vista)
  • %Application Data%\Microsoft\CryptnetUrlCache\Content\{random 4} (Versions lower than Windows Vista)

It does not have rootkit capabilities.

It does not exploit any vulnerability.

  SOLUTION

Minimum Scan Engine:

9.700

VSAPI OPR PATTERN File:

11.177.00

VSAPI OPR PATTERN Date:

28 Sep 2014

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

Identify and terminate files detected as TROJ_DLOADER.DNO

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 4

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\Run
    • winlogin = "%User Temp%\winlogin.exe"

Step 5

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.

  • In HKEY_CURRENT_USER\Software\Microsoft\Active Setup\Installed Components
    • 05F16C88-71D3-42C1-BB4F-E9BAF7DB4A9E
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\SystemCertificates\AuthRoot\Certificates
    • B1BC968BD4F49D622AA89A81F2150152A41D829C

Step 6

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.  
  • %Application Data%\Microsoft\Crypto\RSA\{User's Security Identifier}\{random 1} (Windows Vista and higher versions) - installing certificate
  • %Application Data%\Microsoft\Crypto\RSA\{User's Security Identifier}\{random 2} (Windows Vista and higher versions)
  • %Application Data%\Microsoft\CryptnetUrlCache\Content\{random 3} (Versions lower than Windows Vista)
  • %Application Data%\Microsoft\CryptnetUrlCache\Content\{random 4} (Versions lower than Windows Vista)

Step 7

Scan your computer with your Trend Micro product to delete files detected as TROJ_DLOADER.DNO. 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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