Analysis by: Kiyoshi Obuchi
ALIASES:

Virus:ALisp/Bursted.BL(Microsoft), Virus.Acad.Bursted.b(Kaspersky), ALS:Acad-T [Trj](Avast)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware

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: 1,797,990 bytes
File Type: LSP
Memory Resident: No
Initial Samples Received Date: 20 Mar 2019
Payload: Hides 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.

Other System Modifications

This Trojan modifies the following registry entries to hide files with Hidden attributes:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
SHOWALL
CheckedValue = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
NOHIDDEN
CheckedValue = "0"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Explorer\
Advanced\Folder\Hidden\
NOHIDDEN
DefaultValue = "0"

Other Details

This Trojan does the following:

  • It appends the contents of {Current AutoCAD search path}\acaddoc.lsp to the following files:
    • {AutoCad's directory containing customization file }\doc.lsp
    • {AutoCad's directory containing customization file }\{Configuration Filename}.mnl
    • {Current .dwg file path}\acaddoc.lsp
  • Used to load and execute the following file:
    • acad2006doc.lsp
  • It turns off echoing
  • It turns on dialog boxes
  • It terminates itself if the malware does not find the following file:
    • {Current AutoCAD search path}\acaddoc.lsp
  • It hides the following files:
    • {AutoCad's directory containing customization file }\doc.lsp
    • {AutoCad's directory containing customization file }\{Configuration Filename}.mnl
    • {Current .dwg file path}\acaddoc.lsp
    • {Current AutoCAD search path}\acaddoc.lsp
  • It undefines and replaces the functionalities of the following AutoCAD commands:
    • qsave(Save current drawing) -> erase(Remove object from drawing)
    • saveas(Save current drawing) -> modifies the current .dwg file and appends the contents of {Current AutoCAD search path}\acaddoc.lsp
    • wblock(Write block) -> princ(Display an expression on the command line or write an expression to an open file)
    • insert(Insert block) -> princ(Display an expression on the command line or write an expression to an open file)
    • pline(Creates a 2D polyline) -> princ(Display an expression on the command line or write an expression to an open file)

NOTES:
This malware arrives to the system as an AutoLISP script bundled with a drawing (.DWG) file. Once the drawing file is opened, AutoCAD then loads and executes this malware.

  SOLUTION

Minimum Scan Engine: 9.850
FIRST VSAPI PATTERN FILE: 14.888.05
FIRST VSAPI PATTERN DATE: 22 Mar 2019
VSAPI OPR PATTERN File: 14.889.00
VSAPI OPR PATTERN Date: 23 Mar 2019

Step 1

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 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 Trojan.ALS.BURSTED.AJP

[ 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

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\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALL
    • From: CheckedValue = "0"
      To: CheckedValue = "User Preference"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\NOHIDDEN
    • From: CheckedValue = "0"
      To: CheckedValue = "User Preference"
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\NOHIDDEN
    • From: DefaultValue = "0"
      To: DefaultValue = "User Preference"

Step 5

Scan your computer with your Trend Micro product to delete files detected as Trojan.ALS.BURSTED.AJP. 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 the following Trend Micro Support pages for more information:


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