EXEStealthv276WebToolMaster

Hunt Hypothesis

This rule detects the presence of a specific web-based tooling artifact, likely used by adversaries to establish persistence or facilitate lateral movement through browser extensions or web shells. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify low-severity footholds that may be overlooked by standard endpoint detections, thereby reducing the risk of undetected adversary activity within the environment.

YARA Rule

rule EXEStealthv276WebToolMaster
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 65 45 78 65 53 74 65 61 6C 74 68 20 56 32 20 2D 20 77 77 77 2E 77 65 62 74 6F 6F 6C 6D 61 73 74 65 72 2E 63 6F 6D 20 59 4F 55 52 20 41 44 20 48 45 52 45 21 50 69 52 41 43 59 20 69 53 20 41 }

condition:
		$a0 at pe.entry_point
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A developer or DevOps engineer uses a portable, unsigned, or minimally stripped version of a web-based management tool (e.g., a custom build of Portainer, KubeSphere UI, or a standalone Grafana binary) that has been compiled with specific optimizations or obfuscation to reduce size, causing it to match the EXEStealth signature.

  • Filter/Exclusion: Whitelist the specific file path or hash of the known legitimate web tool binaries (e.g., C:\Tools\Portainer\portainer.exe) and exclude files located in standard application directories like C:\Program Files\ or C:\Apps\ if the tool is installed via a standard installer.

• Scenario: An IT administrator runs a lightweight, single-file web server or dashboard (such as Caddy, LiteServer, or a custom Node.js-based admin panel) from a network share or USB drive for quick internal testing or temporary hosting, where the executable is not signed by a major vendor and matches the stealth characteristics.

  • Filter/Exclusion: Exclude processes where the parent process is a known terminal or file explorer (e.g., cmd.exe, powershell.exe, explorer.exe) and the executable path resides in a designated “Tools” or “Temp” directory, or add an exclusion for known lightweight web server binaries like caddy.exe or liteserver.exe.

• Scenario: A CI/CD pipeline or automated build agent executes a custom, statically linked web-based testing harness or mock server (e.g., a Go or Rust binary compiled with -ldflags "-s -w" to strip symbols) that serves as a local endpoint for integration tests, triggering the rule due to its small size and lack of standard PE metadata.

  • Filter/Exclusion: Exclude executables