An external vulnerability scan is a technical assessment that identifies security weaknesses in an organization’s internet-facing digital infrastructure. These weaknesses can range from simple configuration errors to critical vulnerabilities in systems such as websites, web applications, email servers, and other publicly accessible assets.
To simulate an attacker’s perspective, security teams perform these scans from outside the target network using automated tools. These tools detect exposed services, identify open ports, and check for known security flaws, such as outdated software and unpatched vulnerabilities.
Table of Contents
- Benefits of Conducting External Vulnerability Scans
- How Security Teams Use External Vulnerability Scans
- How External Vulnerability Scanning Works
- Difference between Internal and External Vulnerability Scans
- Types of Internal and External Vulnerability Scanning Tools
- Key Takeaways
- FAQs
Benefits of Conducting External Vulnerability Scans
Leaving doors and windows unlocked invites unwanted access—just like unprotected systems, which expose organizations to cyber threats.
Conducting external vulnerability scans helps mitigate this risk by proactively identifying security issues that could potentially lead to breaches or service disruptions. These scans also provide organizations a clearer picture of their external attack surface and help ensure defenses against potential threats are robust.
More specifically, external vulnerability scans offer these benefits:
- Reveal potentially dangerous open ports and services
- Uncover systems running outdated or vulnerable software
- Identify misconfigurations in web applications and other systems
- Detect common vulnerabilities, including some instances of SQL injection and cross-site scripting
- Generate detailed reports that allow security teams to prioritize risks and reduce the likelihood of attacks
How Security Teams Use External Vulnerability Scans
While the ultimate goal remains the same (i.e., protecting an organization from security threats and incidents), external vulnerability scans serve different purposes for different security teams. Let’s take a look at how blue and red teams utilize these scans.
Blue Team
The blue team is responsible for defending an organization against cyberattacks. Their role includes implementing defensive security measures, such as regular external vulnerability scans.
While there is no universally accepted frequency for vulnerability scanning, many organizations conduct scans at least monthly or quarterly. Some also deploy tools for continuous scanning. Frequent scans allow security teams to detect and patch potential weaknesses early—helping ensure ongoing visibility into their security posture.
There are also times when off-schedule scans have to be performed, such as after network changes and after critical security patches are deployed. These event-driven scans help blue teams verify if new patches or network infrastructure (or any significant change, for that matter) did not introduce new vulnerabilities.
Regardless of timing, blue teams typically avoid running intensive scans during critical business operations. Instead, they schedule them during off-peak hours to minimize service disruptions.
Red Team
While the blue team defends an organization from the inside, the red team adopts the perspective of an attacker. Their main objective is to simulate real-world attacks with the goal of uncovering cracks in an organization’s external-facing digital infrastructure.
The red team engages in activities like penetration testing and vulnerability exploitation. But before they can proceed with these, they often first need to identify security flaws through an external vulnerability scan.
Red teams do not typically perform vulnerability scans on a fixed schedule like blue teams do. Instead, they conduct scans as needed. The goal? To assess how effectively the blue team can defend against a real attack.
How External Vulnerability Scanning Works
An external vulnerability scan is just one type of vulnerability assessment. However, regardless of the type, the typical process follows these steps:
- Identifying assets and enriching them with contextual information, such as the technologies running on them
- Scanning the discovered assets and technologies for security issues
- Comparing the issues against a vulnerability database that records common vulnerabilities and exposures (CVEs)
- Validating and prioritizing vulnerabilities based on severity, exploitability, and potential impact
- Alerting the security team when a security issue discovered is critical and requires urgent attention
- Re-scanning after remediation to verify that fixes have been successfully implemented
Difference between Internal and External Vulnerability Scans
Vulnerability scanning can be categorized by scope—internal or external. Here’s a TL;DR version of the difference between internal and external vulnerability scanning, along with some relevant tools for each.
| Characteristic | External Scan | Internal Scan |
| Purpose | Protect against external threats | Protect against internal threats |
| Scope | Internet-facing assets (e.g., websites, email servers, firewalls) | Internal systems (e.g., workstations, databases, network devices, printers) |
| Frequency | – Regularly scheduled (monthly or quarterly) – Can be continuous in the context of external attack surface management (EASM) – After network changes or critical patch releases – On demand (e.g., as part of red team exercises) | – Regularly scheduled (monthly or quarterly) – After network changes or critical patch releases – When new hardware is installed |
| Tools | – Dynamic application security testing (DAST) tools – EASM platforms – Data security solutions | – Network discovery tools – Static application security testing (SAST) – Endpoint detection and response (EDR) solutions – Data security solutions – Agent-based vulnerability scanner |
External Scans
External vulnerability scanning focuses on what a threat actor can see from the Internet when they try to infiltrate an organization’s external infrastructure. These scans can discover security issues, such as:
- Open ports and unnecessary services
- Outdated versions of web servers, email servers, or other software that contain known vulnerabilities
- Web application vulnerabilities
- Misconfigured firewalls, web servers, and other systems that can compromise sensitive data
- Weak passwords or default credentials on publicly accessible systems
- DNS-related security issues like DNS zone transfer vulnerabilities
- Weak cipher suites, expired certificates, and other Secure Sockets Layer/Transport Layer Security (SSL/TLS) misconfigurations
External scans are performed without any authentication or access to the organization’s systems (ie., uncredentialed scanning). Some of the most common techniques used in these scans are port scanning and web application scanning.
Internal Scans
As the name suggests, internal vulnerability scanning focuses on non-web-facing assets such as databases, endpoints (e.g., desktops, laptops, and mobile devices), and storage systems. But why do these components need to be scanned?
One reason is to identify internal security risks and issues such as infected devices within the network perimeter, unsecured shared folders, or unencrypted sensitive data stored on internal servers. These vulnerabilities can expose critical resources to unauthorized access or compromise.
Another key purpose is to detect signs of an attacker’s lateral movement, including the presence of known indicators of compromise (IoCs) or malware signatures. Internal scans can also uncover weaknesses that facilitate lateral movement, such as weak or reused credentials and unpatched third-party systems, both of which attackers could exploit to escalate privileges and move deeper into the network.
Types of Internal and External Vulnerability Scanning Tools
Vulnerability scanning tools vary in scope and functionality. Some tools are primarily designed for internal scanning (e.g., SAST tools and EDR solutions), while others are commonly used for external scans (e.g., DAST tools and EASM platforms). Other tools can perform both internal and external scans, but even then, each tool has specific areas of focus. Below is a comparison of common tools used by security teams.
| Solution | Pros | Cons | Type of Scan |
| DAST tools | Finds runtime vulnerabilities like SQL injection and cross-site scripting (XSS) vulnerabilities; no source code access needed | Limited coverage compared with static analysis; may produce false positives; can disrupt live applications | Primarily external scan |
| EASM platforms | Provides a comprehensive view of the external attack surface; helps discover shadow IT; combines passive and active scanning techniques | Can generate a large volume of data; effectiveness depends on the accuracy of discovery algorithms | External scan |
| Network discovery tools | Maps IP address network topology; discovers unknown devices; essential for asset inventory | Can generate significant network traffic and affect performance | Primarily internal |
| SAST tools | Can identify vulnerabilities before an application is compiled or deployed | Cannot detect vulnerabilities that manifest only during runtime | Internal scan |
| EDR solutions | Provides detailed endpoint visibility; enables rapid incident response | Can generate a large volume of data so may affect endpoint performance | Internal scan |
| Data security solutions | Prevents unauthorized access to sensitive data; helps comply with data privacy regulations | Can be complex to implement; may impact data accessibility | Can be internal and external, depending on data location |
| Agent-based vulnerability scanners | Provides deep visibility into system-level vulnerabilities; effective for remote or offline systems; Bypasses network restrictions like firewalls | Requires agent deployment and management; may impact system performance; can raise privacy concerns | Internal scan |
Key Takeaways
- External vulnerability scans proactively identify weaknesses in internet-facing systems.
- These scans simulate an attacker’s perspective, helping security teams assess exposure to external threats.
- Blue teams use external vulnerability scans to monitor for vulnerabilities and strengthen defenses, while red teams conduct them to identify exploitable weaknesses for simulated attacks.
- External vulnerability scans detect security risks such as open ports, outdated software, misconfigurations, and web application vulnerabilities.
- Tools like EASM and DAST secure internet-facing assets, while EDR and agent-based scanners protect internal systems.
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FAQs
How Do External Vulnerability Scans Differ from Risk Assessments?
External vulnerability scans are technical assessments that aim to detect security weaknesses in external systems—they pinpoint what vulnerabilities exist. Risk assessments, on the other hand, are broader. They analyze how likely a vulnerability will be exploited and what the consequences would be.
What Is a Credentialed versus Uncredentialed Scan?
Credentialed scans involve providing the vulnerability scanner with login credentials to access systems. They allow security experts to identify vulnerabilities that require privileged access and are common in internal scans.
Meanwhile, uncredentialed scans are performed without requiring a system login. They are commonly used in external vulnerability scans, where analysts simulate an external attacker’s perspective to identify security issues accessible without authentication.
What Happens after Performing an External Vulnerability Scan?
The rest of the real work begins—analyzing vulnerabilities, prioritizing risks, and implementing remediation measures. Vulnerability scanning is only a step in the whole vulnerability assessment process. Security teams must now test, analyze, and rank vulnerabilities, create a remediation plan, and document their actions.