In the context of the CompTIA PenTest+ certification and the domain of Vulnerability Discovery and Analysis, Nessus, developed by Tenable, stands as one of the industry's most ubiquitous proprietary vulnerability scanners. It serves as a critical tool for security professionals to automate the proc…In the context of the CompTIA PenTest+ certification and the domain of Vulnerability Discovery and Analysis, Nessus, developed by Tenable, stands as one of the industry's most ubiquitous proprietary vulnerability scanners. It serves as a critical tool for security professionals to automate the process of identifying security flaws, configuration issues, and malware within an IT infrastructure.
Functionally, Nessus operates by utilizing a vast database of "plugins," which are individual scripts designed to check for specific vulnerabilities or Common Vulnerabilities and Exposures (CVEs). During a penetration test, an analyst typically configures Nessus to perform various types of scans. These range from basic Discovery Scans (identifying live hosts and open ports) to comprehensive Vulnerability Scans.
A key distinction emphasized in PenTest+ is the difference between non-credentialed and credentialed scans. A non-credentialed scan simulates an external attacker with no privileges, identifying surface-level vulnerabilities accessible from the network. Conversely, a credentialed scan allows Nessus to log into the target system, providing a deeper analysis of the registry, file systems, and installed software versions, leading to fewer false positives and a more accurate risk assessment.
Nessus also supports compliance auditing (checking against benchmarks like CIS or DISA STIGs) and allows for the customization of scan policies to balance network traffic load and scan depth. Upon completion, it generates detailed reports categorizing vulnerabilities by severity (Critical, High, Medium, Low, Info) often based on CVSS scores. For a penetration tester, interpreting Nessus output is vital for the Analysis phase, requiring the verification of findings to eliminate false positives before exploiting them or recommending remediation strategies. Ultimately, mastery of Nessus is essential for efficient vulnerability assessment and effective reporting.
Comprehensive Guide to Nessus Vulnerability Scanner for CompTIA PenTest+
What is the Nessus Vulnerability Scanner? Nessus, developed by Tenable, is the industry standard for vulnerability assessment. In the context of the CompTIA PenTest+ exam, it serves as a primary tool for the Vulnerability Discovery phase. It is an automated tool designed to scan computers and networks to detect known vulnerabilities, misconfigurations, and missing patches. Unlike a simple port scanner (like Nmap), Nessus probes services to determine if they are running vulnerable versions or have insecure settings.
Why is it Important? Nessus is critical for both penetration testers and defenders because it automates the tedious process of checking against thousands of known Common Vulnerabilities and Exposures (CVEs). It provides a baseline of security posture, helps in compliance auditing (PCI-DSS, HIPAA), and prioritizes remediation efforts based on severity. In the exam, understanding Nessus is vital for analyzing scan results and determining the difference between a true vulnerability and a false positive.
How Nessus Works Nessus operates using a client-server architecture and relies heavily on Plugins. Plugins are small programs written in the Nessus Attack Scripting Language (NASL) that check for specific flaws.
The scanning process generally follows these steps: 1. Host Discovery: Identifies live hosts using ping, ARP, etc. 2. Port Scanning: Determines which ports are open (often integrating Nmap). 3. Service Detection: Interrogates open ports to identify running applications and versions. 4. Vulnerability Assessment: Compares findings against a database of plugins. This can be done in two modes: - Non-credentialed Scan: Scans from the outside, seeing what a hacker sees without access. It is limited to network services and remote exploits. - Credentialed Scan: The scanner logs into the target system to audit local patch levels, registry keys, and configuration files. This is more accurate and produces fewer false positives.
Exam Tips: Answering Questions on Nessus vulnerability scanner The CompTIA PenTest+ exam will likely test your ability to interpret Nessus output and configure scans correctly. Keep these tips in mind:
1. Differentiating Scan Types If an exam scenario describes a scan that missed missing patches or local configuration errors, the answer is usually that a Non-credentialed scan was performed. To fix this, you must select Credentialed scanning.
2. Interpreting Output and Logs You may be presented with a screenshot or text log of a vulnerability finding. Look for the Plugin Output section. If the output shows a version number (e.g., 'Apache 2.4.1') that is lower than the fixed version, it is a valid finding. If the output relies solely on a banner grab that might be faked, consider it a potential False Positive.
3. Managing False Positives If a question asks how to handle a vulnerability listed as 'Critical' but the system is not actually vulnerable (e.g., a backported patch was applied but the version number didn't change), the correct action is to verify the finding manually and then mark it as a False Positive in the report.
4. Safe Checks vs. Aggressive Scans Be aware of the configuration setting Safe Checks. If a client requires that production services must not go down during a pentest, you must ensure 'Safe Checks' are enabled to prevent Nessus from running plugins that might crash the target (Denial of Service).
5. Severity Levels Nessus categorizes findings as Info, Low, Medium, High, and Critical. In exam questions asking which vulnerability to prioritize, focus on Critical and High vulnerabilities, especially those with available public exploits.