Automated vulnerability scanners help you quickly identify security flaws across your networks, hosts, and applications. This guide covers best practices for deploying these tools, understanding their results, and validating your findings to ensure a secure environment.
flowchart TD
A["Define Scope (Depth & Breadth)"] --> B[Automated Scanning]
B --> C{Scan Type}
C -->|Network| D[Port & Service Discovery]
C -->|Web App| E[Crawling & Flaw Detection]
C -->|Passive| F[Metadata & Traffic Analysis]
D --> G[Correlate Results]
E --> G
F --> G
G --> H[Manual Validation]Setting Your Scope
Before running any automated tools, you need to define the boundaries of your test. A well-scoped scan prevents accidental disruptions and ensures you gather the right data.
Breadth: What are you testing? This includes target networks, specific segments, host machines, or application inventories.
Depth: How thoroughly are you testing? This determines whether you are just checking if a vulnerability is visible from the outside, or if you are using authenticated access to dig deeper into the system.
Always validate your scope before and after testing. For example, if your breadth included 100 machines, verify that all 100 were actually online and reachable during the scan.
Types of Automated Scanners
Automated testing utilizes software to interact with a target, examine responses, and flag potential vulnerabilities. This drastically reduces the time required compared to manual checks.
Network and General Scanners
Network scanners help you obtain a basic overview of what is available on your target network.
Port-Based Scanners: These tools check all 65,535 possible network ports to see if they are "Open" (able to receive data) or "Closed". If a port is open, the scanner makes an educated guess about potential vulnerabilities based on standard port usage (e.g., flagging port 23 for insecure Telnet).
Service-Based Scanners: These are more precise. Instead of just looking at the port number, they communicate using different protocols to verify exactly what service is running (e.g., confirming that port 8000 is actually running an HTTP web server).
Banner Grabbing: The scanner connects to a port and reads the identification string returned by the host, which often reveals the specific application name and version number.
Web Application Scanners
Web app scanners start with a URL and crawl the site by following links and directory structures.
Once the site is mapped, the scanner performs audits against the discovered pages. It might attempt SQL injection on form fields, look for cross-site scripting (XSS) vulnerabilities, or check for sensitive information leaked in error messages.
Watch out for Denial of Service (DoS)
Scanners often use "Directory Brute Forcing" to guess hidden folder names. Because this sends thousands of rapid requests, it can overwhelm and crash a production web server. Always monitor server health closely when running these scans.
Insecure HTTP Methods
Web scanners will often check for insecure web server methods that could allow attackers to manipulate your site.
| HTTP Method | Potential Risk |
|---|---|
| OPTIONS | While not inherently dangerous, it allows attackers to easily see which other HTTP methods your server accepts. |
| PUT / DELETE | If misconfigured, attackers could use PUT to upload malicious files, or DELETE to remove your web content. |
| WebDAV | These extensions (like PROPFIND or MKCOL) interact with core OS components and can expose systems to buffer overflows or privilege escalation. |
| TRACE | Contains a flaw that can echo requests back to the client, leading to unauthorized information disclosure. |
Protocol-Specific Scanners
Conventional scanners often fail to negotiate complex protocols. You may need specialized tools for:
VPNs: To accurately fingerprint Internet Key Exchange (IKE) devices and identify weak pre-shared keys.
VoIP / Voice Networks: To ensure voice networks are properly segmented and cannot be leveraged to access core infrastructure.
Validating Scan Results
Automated tools are incredibly efficient, but they are prone to false positives (flagging a vulnerability that doesn't actually exist). You should never rely solely on automated output without validation.
- 1
Correlate your findings
If you use multiple tools, group the results to avoid skewed risk profiles. You can correlate specifically (grouping by exact CVE or vulnerability ID) or categorically (grouping by compliance frameworks, like NIST password complexity rules).
- 2
Consult vulnerability databases
Cross-reference the reported CVEs (Common Vulnerabilities and Exposures) with public databases like OSVDB, Bugtraq, or vendor advisories. Ensure the vulnerability actually applies to your specific OS and environment.
- 3
Test in an isolated lab
Whenever possible, set up a virtual machine (VM) replica of the target environment. Testing exploits in an isolated lab ensures your findings are reliable and prevents accidental damage to production systems.
- 4
Perform manual visual confirmation
Manually connect to the flagged service or application. Visually inspecting the target helps identify custom logic or uncommon port configurations that the automated scanner may have misunderstood.
Passive Scanning Techniques
Not all scanning requires direct interaction with the target. Passive techniques gather information without triggering intrusion detection systems (IDS).
Metadata Analysis
Files (like Microsoft Office documents) often contain hidden metadata such as author names, internal server paths, creation dates, and internal IP addresses. Scanners can extract this data from publicly available documents to map out internal structures. Always purge metadata before publishing documents.
Traffic Monitoring
By connecting to an internal network and silently capturing data, you can analyze traffic offline. Misconfigured switches (like those with improper ARP cache timing) or load balancers can leak sensitive data across the network without any active probing.
Check for Default Passwords
Automated scanners might miss simple human errors. Always manually check identified systems against online databases of common, default, or backdoor passwords. Many breaches occur simply because an administrator never changed the factory default credentials.