Home/ATT&CK Technique/Trusted Developer Utilities Proxy Execution
ATT&CK Technique

Trusted Developer Utilities Proxy Execution

T1127 · stealth, execution

Adversaries may take advantage of trusted developer utilities to proxy execution of malicious payloads. There are many utilities used for software development related tasks that can be used to execute code in various forms to assist in development, debugging, and reverse engineering. These utilities may often be signed with legitimate certificates that allow them to execute on a system and proxy execution of malicious code through a trusted process that effectively bypasses application control solutions.

Smart App Control is a feature of Windows that blocks applications it considers potentially malicious from running by verifying unsigned applications against a known safe list from a Microsoft cloud service before executing them. However, adversaries may leverage "reputation hijacking" to abuse an operating system’s trust of safe, signed applications that support the execution of arbitrary code. By leveraging Trusted Developer Utilities Proxy Execution to run their malicious code, adversaries may bypass Smart App Control protections.

Windows
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Actors Using This

1
chinaWorok
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Atomic Tests

2
Executable Atomic Red Team test cases for exercising this technique in a lab. Copy a command, run it on the listed platform, confirm your detections fire.
command_promptwindowsLolbin Jsc.exe compile javascript to exe
Use jsc.exe to compile javascript code stored in scriptfile.js and output scriptfile.exe. https://lolbas-project.github.io/lolbas/Binaries/Jsc/ https://www.phpied.com/make-your-javascript-a-windows-exe/ 
copy "#{filename}" %TEMP%\hello.js
#{jscpath}\#{jscname} %TEMP%\hello.js
command_promptwindowsLolbin Jsc.exe compile javascript to dll
Use jsc.exe to compile javascript code stored in Library.js and output Library.dll. https://lolbas-project.github.io/lolbas/Binaries/Jsc/ https://www.phpied.com/make-your-javascript-a-windows-exe/ 
copy "#{filename}" %TEMP%\LibHello.js
#{jscpath}\#{jscname} /t:library %TEMP%\LibHello.js
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Mitigations

3
MITRE ATT&CK mitigations - vendor-agnostic guidance for reducing exposure to this technique.
M1021Restrict Web-Based Content

Restricting web-based content involves enforcing policies and technologies that limit access to potentially malicious websites, unsafe downloads, and unauthorized browser behaviors. This can include URL filtering, download restrictions, script blocking, and extension control to protect against exploitation, phishing, and malware delivery.

Deploy Web Proxy Filtering
  • Use solutions to filter web traffic based on categories, reputation, and content types.
  • Enforce policies that block unsafe websites or file types at the gateway level.
Enable DNS-Based Filtering
  • Implement tools to restrict access to domains associated with malware or phishing campaigns.
  • Use public DNS filtering services to enhance protection.
Enforce Content Security Policies (CSP)
  • Configure CSP headers on internal and external web applications to restrict script execution, iframe embedding, and cross-origin requests.
Control Browser Features
  • Disable unapproved browser features like automatic downloads, developer tools, or unsafe scripting.
  • Enforce policies through tools like Group Policy Management to control browser settings.
Monitor and Alert on Web-Based Threats
  • Use SIEM tools to collect and analyze web proxy logs for signs of anomalous or malicious activity.
  • Configure alerts for access attempts to blocked domains or repeated file download failures.
M1038Execution Prevention

Prevent the execution of unauthorized or malicious code on systems by implementing application control, script blocking, and other execution prevention mechanisms. This ensures that only trusted and authorized code is executed, reducing the risk of malware and unauthorized actions.

Application Control
  • Use Case: Use tools like AppLocker or Windows Defender Application Control (WDAC) to create whitelists of authorized applications and block unauthorized ones. On Linux, use tools like SELinux or AppArmor to define mandatory access control policies for application execution.
  • Implementation: Allow only digitally signed or pre-approved applications to execute on servers and endpoints. (e.g., `New-AppLockerPolicy -PolicyType Enforced -FilePath "C:\Policies\AppLocker.
xml"`) Script Blocking
  • Use Case: Use script control mechanisms to block unauthorized execution of scripts, such as PowerShell or JavaScript. Web Browsers: Use browser extensions or settings to block JavaScript execution from untrusted sources.
  • Implementation: Configure PowerShell to enforce Constrained Language Mode for non-administrator users. (e.g.
, Set-ExecutionPolicy AllSigned) Executable Blocking
  • Use Case: Prevent execution of binaries from suspicious locations, such as %TEMP% or %APPDATA% directories.
  • Implementation: Block execution of .exe, .bat, or .ps1 files from user-writable directories.
Dynamic Analysis Prevention
  • Use Case: Use behavior-based execution prevention tools to identify and block malicious activity in real time.
  • Implemenation: Employ EDR solutions that analyze runtime behavior and block suspicious code execution.
M1042Disable or Remove Feature or Program

Disable or remove unnecessary and potentially vulnerable software, features, or services to reduce the attack surface and prevent abuse by adversaries. This involves identifying software or features that are no longer needed or that could be exploited and ensuring they are either removed or properly disabled.

Remove Legacy Software
  • Use Case: Disable or remove older versions of software that no longer receive updates or security patches (e.g., legacy Java, Adobe Flash).
  • Implementation: A company removes Flash Player from all employee systems after it has reached its end-of-life date.
Disable Unused Features
  • Use Case: Turn off unnecessary operating system features like SMBv1, Telnet, or RDP if they are not required.
  • Implementation: Disable SMBv1 in a Windows environment to mitigate vulnerabilities like EternalBlue.
Control Applications Installed by Users
  • Use Case: Prevent users from installing unauthorized software via group policies or other management tools.
  • Implementation: Block user installations of unauthorized file-sharing applications (e.g., BitTorrent clients) in an enterprise environment.
Remove Unnecessary Services
  • Use Case: Identify and disable unnecessary default services running on endpoints, servers, or network devices.
  • Implementation: Disable unused administrative shares (e.g., C$, ADMIN$) on workstations.
Restrict Add-ons and Plugins
  • Use Case: Remove or disable browser plugins and add-ons that are not needed for business purposes.
  • Implementation: Disable Java and ActiveX plugins in web browsers to prevent drive-by attacks.
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Detection Coverage

2/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) 19
Analytics (MITRE CAR) 1
Runtime / container (Falco) none
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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CAR Analytics

1
MITRE Cyber Analytics Repository - field-tested detection logic for this technique, written as pseudocode/queries you adapt to your own SIEM (Splunk, Sentinel, EQL). Each is a ready starting point for a detection rule, not just a description.
CAR-2020-11-008High coverageMSBuild and msxsl

Trusted developer utilities such as MSBuild may be leveraged to run malicious code with elevated privileges. This analytic looks for any instances of msbuild.exe, which will execute any C# code placed within a given XML document.

and msxsl.exe, which processes xsl transformation specifications for XML files and will execute a variaty of scripting languages contained within the XSL file. Both of these executables are rarely used outside of Visual Studio.

Pseudocode - Pseudocode - msbuild
processes = search Process:Create
target_processes = filter processes where (
  (exe="C:\Program Files (x86)\Microsoft Visual Studio\*\bin\MSBuild.exe" OR exe="C:\Windows\Microsoft.NET\Framework*\msbuild.exe" OR exe="C:\users\*\appdata\roaming\microsoft\msxsl.exe") AND
  image_path!="*Microsoft Visual Studio*")
output target_processes
Splunk - Splunk Search - msbuild
(index=__your_sysmon_index__ EventCode=1) (Image="C:\\Program Files (x86)\\Microsoft Visual Studio\\*\\bin\\MSBuild.exe" OR Image="C:\\Windows\\Microsoft.NET\\Framework*\\msbuild.exe" OR Image="C:\\users\\*\\appdata\\roaming\\microsoft\\msxsl.exe") ParentImage!="*\\Microsoft Visual Studio*")
LogPoint - LogPoint Search - msbuild
norm_id=WindowsSysmon event_id=1 (image IN ["C:\Program Files (x86)\Microsoft Visual Studio\*\bin\MSBuild.exe", "C:\Windows\Microsoft.NET\Framework*\msbuild.exe", "C:\Users\*\appdata\roaming\microsoft\msxsl.exe") -parent_image="*\Microsoft Visual Studio*")
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