Vulnerability scanning and penetration testing are two complementary methods of assessing your security. A vulnerability scan is an automated process that searches networks and systems for issues such as misconfigurations or outdated software. A penetration test goes a step further: once the pen tester has compiled a list of vulnerabilities, they will attempt to exploit them in a simulation of a real-world cyberattack.
Because a penetration test relies on a high level of manual effort, the typical pen test is more time- and labor-intensive than a vulnerability scan. It’s also more thorough, as a pen tester can seek out issues an automated tool might not be able to uncover.
A vulnerability scan requires less time and effort than a pen test, making it possible for companies to run scans on a weekly, daily, or even a continuous basis. Many organizations use both techniques in tandem, coupling continuous scanning with an annual penetration test.
In this article, we’ll discuss each method in turn, before digging into how they compare.
Vulnerability Scanning
A vulnerability scan searches a target network or system for vulnerabilities, checking for open ports, weak passwords, configuration errors, outdated software, and any other weakness that an attacker could exploit. To identify issues, these tools rely on databases of existing vulnerabilities, such as the Common Vulnerabilities and Exposures (CVE) list and the National Vulnerability Database (NVD).
Most scanners present their findings in a clear, legible dashboard, scoring vulnerabilities based on risk so that you can prioritize the most dangerous issues first. Though they are chiefly focused on detection, some tools, such as Nessus, offer remediation guidance and tracking as well.
Many of these automated scanners can run continuously, detecting issues and anomalies in real time. They’ll turn up their share of false positives, though, and may miss some issues a security professional would notice. Not every ‘vulnerability’ a scan turns up can actually be exploited by an attacker. This can lead to a fair bit of overhead, as your IT staff has to investigate the issues.
Penetration Testing
A penetration test is a full-on simulated attack on a system, in which the pen tester identifies vulnerabilities and then attempts to exploit them. Once finished, they will compile their findings into a report, which the organization being tested can then use to improve their security.
Pen testers will often use vulnerability scanners as part of their discovery process. They’ll also use tools such as Nmap to map networks and Metasploit to try out different exploits. These tools are adjacent to vulnerability scanners, with a key difference: they do not spotlight vulnerabilities on their own. Instead, they gather information that a skilled professional can then use in their hunt for vulnerabilities.
Once the pen tester has their list of vulnerabilities, they launch their simulated attacks in earnest. They’ll try anything from SQL injections to phishing emails as they attempt to break into the system – anything a hacker might try, a pen tester will replicate.
Once they make a breakthrough, pen testers will pivot their attacks – what else can they attempt from their new vantage point? Once a pen tester has broken into a system, they might see if a credentialed vulnerability scan would uncover any vulnerabilities an uncredentialed scan may have missed.
Penetration tests come in several different types. The broadest distinction is between black box testing, in which the pen tester starts with minimal knowledge of or access to the system being tested, and white box testing, in which the pen tester starts with broad access.
Comparing Vulnerability Scanning & Penetration Testing
Vulnerability scanning and penetration testing both work towards the same overarching goal: by understanding their weaknesses, a business can strengthen its security posture. Both approaches work together well, but there are some key differences between the two.
Crucially, pen testing requires a high level of manual effort. That makes a pen test more time-intensive and costly than a vulnerability scan, and it also means you can’t run a pen test every day. Pen testing should be scheduled on a recurring basis, but it usually runs closer to an annual than a weekly cadence.
Vulnerability scanning is typically automated, making an individual scan much faster and cheaper than a pen test. That makes it viable to run scans on a weekly, daily, or even continuous basis. Constant scanning will still use computing resources and require administrative overhead, and the costs can add up; a year of continuous scanning can prove more expensive than a once-a-year pen test.
Because pen tests simulates real world attacks, they have the potential to disrupt business operations. Many pen testers will mitigate this by running their tests in a staging environment, or by scheduling them in a business’s off-hours. Vulnerability scans do not attempt to exploit vulnerabilities, so they cause minimal disruption beyond computing and administration overhead.
As you can see, both of these approaches are complementary. An annual pen test will really put your security systems through their paces, and will often identify issues an automated scan wouldn’t surface. Vulnerability scanning, on the other hand, can be deployed year-round, allowing for continuous coverage to identify new issues as they arise.
As such, many compliance standards require regularly scheduled pen testing in tandem with continuous vulnerability scanning. In some cases, smaller businesses might be able to get by with just vulnerability scanning. But the most secure approach uses a combination of both vulnerability scanning and penetration testing, enabling a company to regularly vet their systems and continuously monitor for new issues.
For more information, see our guide to the top pen testing services.
Comparison Table
| Vulnerability Scanning | Penetration Testing |
| Automated | Manual |
| Limited computing and administrative overhead | Time- and labor-intensive |
| Can be scheduled on a weekly, daily, or continuous basis | Typically scheduled on an annual basis |
| Passive scan is unlikely to disrupt operations | Simulated attacks can disrupt business operations |
| Turns up some false positives | Pen testers verify vulnerabilities in their attempts to exploit them |