Disclosed hacktool set - file s.exe

Hunt Hypothesis

This detection identifies adversaries deploying executable files named “s.exe” that exhibit characteristics of disclosed hacking tools, indicating potential reconnaissance or post-compromise activity. Proactively hunting for this behavior in Azure Sentinel is critical to identify early-stage threats leveraging common tool names to evade initial scrutiny and prevent lateral movement within the environment.

YARA Rule

rule Hacktools_CN_WinEggDrop {
	meta:
		description = "Disclosed hacktool set - file s.exe"
		author = "Florian Roth"
		date = "17.11.14"
		score = 60
		hash = "7665011742ce01f57e8dc0a85d35ec556035145d"
	strings:
		$s0 = "Normal Scan: About To Scan %u IP For %u Ports Using %d Thread" fullword ascii
		$s2 = "SYN Scan: About To Scan %u IP For %u Ports Using %d Thread" fullword ascii
		$s6 = "Example: %s TCP 12.12.12.12 12.12.12.254 21 512 /Banner" fullword ascii
		$s8 = "Something Wrong About The Ports" fullword ascii
		$s9 = "Performing Time: %d/%d/%d %d:%d:%d --> " fullword ascii
		$s10 = "Example: %s TCP 12.12.12.12/24 80 512 /T8 /Save" fullword ascii
		$s12 = "%u Ports Scanned.Taking %d Threads " fullword ascii
		$s13 = "%-16s %-5d -> \"%s\"" fullword ascii
		$s14 = "SYN Scan Can Only Perform On WIN 2K Or Above" fullword ascii
		$s17 = "SYN Scan: About To Scan %s:%d Using %d Thread" fullword ascii
		$s18 = "Scan %s Complete In %d Hours %d Minutes %d Seconds. Found %u Open Ports" fullword ascii
	condition:
		5 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 4 specific false positive scenarios for the “Disclosed hacktool set - file s.exe” detection rule, along with recommended filters:

• Scenario: Legitimate deployment of SolarWinds Patch Manager or similar update agents. These tools often create a temporary executable named s.exe (or s_update.exe) in the %TEMP% directory to apply patches during scheduled maintenance windows.

  • Suggested Filter: Exclude processes where the parent process is PatchManagerService.exe and the file path contains \AppData\Local\Temp\. Additionally, whitelist the specific SHA-256 hash of the known good s.exe binary used by your organization’s patching solution.

• Scenario: Execution of Microsoft System Center Configuration Manager (SCCM) or Intune compliance scripts. During routine inventory collection or software installation tasks, SCCM agents frequently spawn a generic helper process named s.exe to execute PowerShell scripts or download payloads.

  • Suggested Filter: Create an exclusion for any s.exe instance where the command line arguments contain keywords like “CCM”, “IntuneManagementExtension”, or specific SCCM site codes (e.g., --site=ABC). Ensure the process is running under a dedicated service account (e.g., DOMAIN\SCCM-Service-Account) rather than an interactive user.

• Scenario: Scheduled maintenance jobs utilizing Sysinternals Suite tools, specifically PsExec or custom batch scripts. IT administrators often use s.exe as a wrapper script for nightly backup verification or log rotation tasks that invoke other utilities like robocopy or vssadmin.

  • Suggested Filter: Implement a time-based exclusion (e.g., allow the rule to trigger only between 08:00 and 17:00) combined with a path filter for known