Reconnaissance and OSINT in Penetration Testing

Hacking doesn't start with a port scan.

The popular image of a cyber attack begins with someone launching Nmap against a target network — green text scrolling down a black screen, open ports appearing one by one. It makes for good cinema. It's also almost entirely wrong.

By the time a skilled attacker sends a single packet to your network, they already know what they're looking for. They know your technology stack, your email address format, the names of your IT administrators, which VPN appliance you run, which cloud provider you use, and possibly the passwords of several of your employees. They gathered all of this without touching your systems — without generating a single log entry, without tripping a single alert.

This is reconnaissance. It's the phase that determines whether an attack succeeds or fails, and it's the phase that most organisations never see, never test, and never think about when evaluating their security posture.

In a well-conducted penetration test, reconnaissance isn't a warm-up exercise before the "real" testing begins. It is the testing — or at least, it's the intelligence-gathering phase that shapes every decision the tester makes from that point forward. Understanding what an attacker can learn about you without ever touching your systems is one of the most valuable things a pen test can deliver.

What reconnaissance and OSINT actually mean.

Reconnaissance is the systematic gathering of information about a target before launching an attack. It's the military term applied to cyber operations: understanding the terrain before committing forces.

OSINT — Open Source Intelligence — is a subset of reconnaissance that uses only publicly available sources. No hacking, no exploitation, no illegal access. Just careful, methodical collection and analysis of information that the target (or third parties) have made publicly available, intentionally or otherwise.

Reconnaissance divides into two categories, and the distinction matters because they carry very different detection profiles:

A penetration tester simulates both phases. But the passive phase is where the strategic advantage is built — and it's the phase that most directly mirrors how real adversaries operate.

Where attackers find your information.

The volume of information available about any organisation through public sources is staggering — and it grows every time someone posts a job advert, pushes code to GitHub, registers a certificate, or creates a LinkedIn profile. Here's what a skilled OSINT practitioner can extract, source by source.

What we found in 90 minutes without touching a system.

To illustrate the power of passive reconnaissance, here's a composite of what we typically uncover during the OSINT phase of an engagement — all gathered before a single active probe is launched. The target is a fictional but representative mid-size UK professional services firm.

Ninety minutes. No packets sent. No alerts generated. And the attacker now knows: the VPN appliance model and version (vulnerable), the email platform (Exchange 2016, approaching end of support), the full technology stack (from a job advert), the IT Director's name and a breached password, database credentials committed to GitHub, internal IP ranges from an indexed PDF, three new starters who are prime phishing targets, and a forgotten staging environment with no WAF.

This isn't exceptional. This is normal. We find intelligence of this quality or better in the majority of engagements.

How recon shapes every subsequent phase.

Reconnaissance isn't a standalone exercise — it directly determines the effectiveness of every phase that follows. The quality of the intelligence gathered in recon is the single largest predictor of whether an attack (or a pen test) succeeds.

The blind spots in your external posture.

Most organisations have some awareness of their external attack surface — they know their main website, their VPN portal, their email server. What they consistently underestimate is the shadow attack surface: the systems, data, and information that exist publicly but aren't on anyone's radar.

The limits of automated discovery.

Vulnerability scanners and automated attack surface monitoring tools are valuable, but they operate in the active reconnaissance domain — they probe systems that are already known. They don't replicate the creative, cross-referencing intelligence work that characterises skilled passive OSINT.

Automated tools find what's technically exposed. Human OSINT finds what's strategically exposed — the intelligence that transforms a scattered collection of technical observations into a coherent attack plan. Both are necessary. Neither is sufficient alone.

Managing your OSINT exposure.

You can't eliminate your OSINT footprint — your organisation exists publicly and some exposure is inherent to doing business. But you can manage it: reducing unnecessary exposure, monitoring for leaked intelligence, and ensuring that the information available to attackers doesn't give them an easy path in.

How recon fits into our testing process.

Reconnaissance isn't a separate deliverable we bolt onto an engagement — it's integrated into the first phase of every external and social engineering assessment we conduct. Here's how it fits into the workflow.

The recon phase typically consumes 15–20% of the total engagement time. It's the highest-leverage time in the entire test — the intelligence gathered here determines the efficiency and effectiveness of everything that follows. Skipping it, or reducing it to a quick Nmap scan, is like navigating without a map.

What you receive from the OSINT phase.

The OSINT findings don't just inform our testing — they're reported to you as a standalone section of the engagement report. This is some of the most immediately actionable intelligence in the entire deliverable, because many of the exposures can be remediated without waiting for the full pen test to complete.

The bottom line.

Reconnaissance is the phase that determines everything. Real attackers spend more time gathering intelligence than they do exploiting vulnerabilities — because good intelligence makes exploitation faster, quieter, and more effective.

A penetration test that skips or rushes the reconnaissance phase is testing blind. It will find vulnerabilities — scanners always do — but it won't find the attack paths: the specific chains of intelligence and weakness that a real adversary would follow from public information to your crown jewels.

The most important thing you can do today is see yourself the way an attacker sees you. The information is already out there. The only question is whether you find it first.