Disclosed hacktool set (old stuff) - from files iissample.exe, nesscan.exe, twwwscan.exe

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging legacy or repurposed hacking tools like iissample.exe and nesscan.exe to establish persistence or conduct reconnaissance within the environment. A proactive search is critical in Azure Sentinel because these specific executables often mimic legitimate system processes, allowing attackers to evade standard signature-based detections while executing malicious payloads that could compromise sensitive data.

YARA Rule

rule _iissample_nesscan_twwwscan {
	meta:
		description = "Disclosed hacktool set (old stuff) - from files iissample.exe, nesscan.exe, twwwscan.exe"
		author = "Florian Roth"
		date = "23.11.14"
		score = 60
		super_rule = 1
		hash0 = "7f20962bbc6890bf48ee81de85d7d76a8464b862"
		hash1 = "c0b1a2196e82eea4ca8b8c25c57ec88e4478c25b"
		hash2 = "548f0d71ef6ffcc00c0b44367ec4b3bb0671d92f"
	strings:
		$s0 = "Connecting HTTP Port - Result: " fullword
		$s1 = "No space for command line argument vector" fullword
		$s3 = "Microsoft(July/1999~) http://www.microsoft.com/technet/security/current.asp" fullword
		$s5 = "No space for copy of command line" fullword
		$s7 = "-  Windows NT,2000 Patch Method  - " fullword
		$s8 = "scanf : floating point formats not linked" fullword
		$s12 = "hrdir_b.c: LoadLibrary != mmdll borlndmm failed" fullword
		$s13 = "!\"what?\"" fullword
		$s14 = "%s Port %d Closed" fullword
		$s16 = "printf : floating point formats not linked" fullword
		$s17 = "xxtype.cpp" fullword
	condition:
		all of them
}

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 11 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the Disclosed hacktool set rule, including suggested filters and exclusions:

• Scenario: Legacy IIS Website Diagnostics via iissample.exe

  • Context: The file iissample.exe is often part of older Microsoft IIS diagnostic suites or legacy web server health checks. In an enterprise environment, this process may be triggered nightly by a scheduled task to generate connectivity reports for the web farm.
  • Filter/Exclusion: Create a detection exclusion based on the Process Name iissample.exe running under the Account NT SERVICE\W3SVC or a dedicated service account (e.g., svc-iis-diag). Additionally, exclude events where the Parent Process is TaskScheduler.exe.

• Scenario: Nessus Vulnerability Scanning Agent (nesscan.exe)

  • Context: nesscan.exe corresponds to the Tenable Nessus scanning agent. When the central management server pushes a vulnerability assessment job, this executable launches on endpoints to scan open ports and installed software. The rule flags it as a “hacktool” because it performs network discovery similar to reconnaissance tools used by attackers.
  • Filter/Exclusion: Exclude nesscan.exe when the Process Command Line contains keywords like --scan, --agent, or specific Nessus UUIDs. Alternatively, whitelist the process path if it resides in a known directory (e.g., C:\Program Files\Tenable\NessusAgent\).

• Scenario: T-Web Security Scanner Execution (twwwscan.exe)

  • Context: twwwscan.exe is frequently associated with legacy web security scanning tools (often used in financial or government sectors) that perform automated compliance checks. This process runs during business hours to audit