This hypothesis targets the presence of unregistered or stealthy web tool executables, which adversaries often deploy to establish persistent access or perform reconnaissance without triggering standard application whitelisting controls. Proactively hunting for these artifacts in Azure Sentinel allows the SOC to identify low-severity footholds that may indicate early-stage intrusion attempts or lateral movement vectors before they escalate into more impactful compromises.
rule EXEStealth276UnregisteredWebtoolMaster
{
meta:
author="malware-lu"
strings:
$a0 = { EB ?? 45 78 65 53 74 65 61 6C 74 68 20 56 32 20 53 68 61 72 65 77 61 72 65 20 }
condition:
$a0
}This YARA rule can be deployed in the following contexts:
This rule contains 1 string patterns in its detection logic.
Scenario: A developer or DevOps engineer runs a standalone, unregistered build of a web-based API testing tool (e.g., Postman, Insomnia, or a custom internal HTTP client) from a local directory or network share to validate staging endpoints. Since the binary is not signed by a major vendor or registered in the software inventory, it matches the “Unregistered” and “Webtool” criteria.
C:\Users\*\Dev\Tools\ or D:\CI\Artifacts\) or exclude processes where the parent process is a known IDE (e.g., code.exe, idea64.exe) or a build agent (e.g., agent.exe).Scenario: An IT administrator executes a portable, unsigned version of a web-based configuration management utility (e.g., a custom PowerShell GUI wrapper or a lightweight Ansible web interface) to patch a legacy server that cannot run standard agents. The tool is copied to a temporary folder (%TEMP% or C:\Temp) for execution, triggering the stealthy/unregistered heuristic.
services.msc, sc.exe, or powershell.exe running as SYSTEM) and the working directory is a known administrative temp path, or add a specific hash-based exclusion for the known portable tool version.Scenario: A QA team member uses an unregistered, open-source web scraping or monitoring tool (e.g., a custom Python-based HTTP monitor compiled to EXE via PyInstaller) to test load balancing performance. The binary is generated locally and not signed, appearing as an unregistered webtool in the process tree.