Transparent Firewall Validation: Obfuscating Target OS Information Against External Reconnaissance

This technical validation is intentionally documented in English for the global engineering community and NIS2 compliance officers.

Overview: Why “Hidden” OS Data is Your First Line of Defense

The conclusion of this validation is clear: By inserting a Transparent Mode Firewall into an existing network, you can effectively obfuscate the Operating System (OS) information of target devices from external attackers.

During the reconnaissance phase of a cyber attack, adversaries use tools like Nmap to identify OS versions and target specific vulnerabilities. Our real-world testing proves that a transparent-mode FortiGate acts as a “digital camouflage,” deceiving scanners and significantly reducing the accuracy of automated reconnaissance.

The Strategic Value: Beyond Just “A Firewall”

• OS Fingerprint Obfuscation: Forces scanners into “guess-mode,” preventing precise exploit targeting.
• Zero Network Design Change: Achieve high-level security by simply “adding” a layer—no IP changes or routing re-designs required.
• Evidence-Based Security: Moving beyond consultant-speak to prove protection via raw packet-level behavior.

Technical Deep Dive: Disrupting the Nmap Fingerprinting Engine

While AI summaries might simply state “OS not detected,” a professional analysis of the Raw Zenmap Logs reveals exactly how the FortiGate transparent engine protects the host. Below is the actual evidence from our validation lab.

1. Evidence: Raw Nmap/Zenmap Signature Scan

Note the “tcpwrapped” status and the “No exact OS matches” warning. This is the sound of an attacker’s reconnaissance failing in real-time.

Starting Nmap 7.98 ( https://nmap.org ) at 2026-03-25 15:20 +0900
Nmap scan report for 192.168.100.100
Host is up (0.0018s latency).
Not shown: 993 closed tcp ports (reset)
PORT     STATE SERVICE      VERSION
135/tcp  open  msrpc          Microsoft Windows RPC
139/tcp  open  netbios-ssn    Microsoft Windows netbios-ssn
445/tcp  open  microsoft-ds?
2000/tcp open  tcpwrapped
5060/tcp open  tcpwrapped
5357/tcp open  http           Microsoft HTTPAPI httpd 2.0 (SSDP/UPnP)
8008/tcp open  http

Aggressive OS guesses: Microsoft Windows 11 21H2 (98%), Microsoft Windows 10 (94%)
No exact OS matches for host (If you know what OS is running on it, see https://nmap.org/submit/ ).

TCP/IP fingerprint:
OS:SCAN(V=7.98%E=4%D=3/25%OT=135%CT=1%CU=37785%PV=Y%DS=1%DC=D%G=Y%M=FC6198%
OS:TM=69C37F66%P=i686-pc-windows-windows)SEQ(SP=102%GCD=1%ISR=104%TI=I%TS=A
OS:)OPS(O1=M5B4NW8ST11%O2=M5B4NW8ST11%O3=M5B4NW8NNT11%O4=M5B4NW8ST11)
...[Full Fingerprint Captured]...

2. Analysis of the “tcpwrapped” Defense

The appearance of “tcpwrapped” on ports 2000 and 5060 confirms that the FortiGate is intercepting the TCP three-way handshake. The firewall validates the connection but refuses to pass application-layer data to the scanner, effectively closing the door before the attacker can peek inside.

3. Predictable Deployment (L1 Timer Consistency)

The strategic advantage of this “surgical” insertion is its predictability. As documented in our Downtime Verification Report, the insertion downtime is strictly tied to the 10-second L1 Link-up timer. This makes it a low-risk, high-reward implementation for production environments.

Strategic Implications for NIS2 Compliance in Finland

For Finnish enterprises navigating NIS2 requirements, the ability to “add” robust reconnaissance protection without a multi-month network migration is a critical competitive edge. Large SIs often overlook these precision-based deployments in favor of massive infrastructure overhauls.

Seeking a non-disruptive security audit or NIS2-compliant architecture?

We specialize in “add-on” security that preserves business continuity while disrupting attacker reconnaissance.
Contact for Deployment Validation

Practical Notes

• Testing was conducted in a controlled environment using FortiGate (Transparent Mode).
• OS obfuscation results may vary depending on deep packet inspection (DPI) settings and target OS versions.
• Real-world downtime was measured at 10.8 seconds, aligning with theoretical L1 recovery intervals.

→ Read our Philosophy: Why we prioritize non-disruptive design