Analysis by: Jennifer Gumban

ALIASES:

Trojan:Win32/Dynamer!ac (Microsoft)

 PLATFORM:

Windows

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet

This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It logs a user's keystrokes to steal information.

It requires its main component to successfully perform its intended routine.

  TECHNICAL DETAILS

File Size: 415,744 bytes
File Type: EXE
Memory Resident: No
Initial Samples Received Date: 06 Aug 2016
Payload: Steals information

Arrival Details

This backdoor 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 backdoor drops the following copies of itself into the affected system:

  • %Program Files%\SAAS Manager\saasmgr.exe - Windows XP
  • %Program Files%\SAAS Manager\saaspost.exe - Windows 7

(Note: %Program Files% is the Program Files folder, where it usually is C:\Program Files on all Windows operating system versions; C:\Program Files (x86) for 32-bit applications running on Windows 64-bit operating systems.)

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
chrome = "{malware path}\{malware name}"

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
chrome = "{malware path}\{malware name}"

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
SAAS Manager = "%Program Files%\SAAS Manager\saasmgr.exe" - Windows XP

HKEY_LOCAL_MACHINE\Software\Microsoft\
Windows\CurrentVersion\Run
SAAS Manager = %Program Files%\SAAS Manager\saaspost.exe - Windows 7

Information Theft

This backdoor logs a user's keystrokes to steal information.

Stolen Information

This backdoor saves the stolen information in the following file:

  • %Application Data%\{CLSID}\Logs\{os}\KB_{random numbers}.dat

(Note: %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.)

Other Details

This backdoor requires its main component to successfully perform its intended routine.

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 12.702.06
FIRST VSAPI PATTERN DATE: 08 Aug 2016
VSAPI OPR PATTERN File: 12.703.00
VSAPI OPR PATTERN Date: 09 Aug 2016

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

Search and delete this file

[ 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%\{CLSID}\Logs\{os}\KB_{random numbers}.dat

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • chrome = "{malware path}\{malware name}"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • chrome = "{malware path}\{malware name}"
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • SAAS Manager = "%Program Files%\SAAS Manager\saasmgr.exe" - Windows XP
  • In HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    • SAAS Manager = %Program Files%\SAAS Manager\saaspost.exe - Windows 7

Step 5

Scan your computer with your Trend Micro product to delete files detected as BKDR_NANOCOR.CU. 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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