Nmap/Short Course/Lecture 11

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Lab: Nmap/Short Course/Lab 11

Summary and Objective

This lecture will explore how Nmap's capabilities can be amplified by using its output and findings in conjunction with other common cybersecurity tools.

Objective: To demonstrate how Nmap can be integrated into a broader security toolchain, using its output to inform packet analysis with Wireshark, guide rule creation for Intrusion Detection Systems like Snort/Suricata, and complement dedicated vulnerability scanners like Nessus/OpenVAS.

Notes

Recap and Power of Tool Integration

Quick Recap of Lecture 10

In our last session, we focused on using Nmap for security auditing and compliance. We discussed how to identify policy violations (like prohibited services or weak SSL/TLS ciphers), detect rogue devices, and verify firewall rules and network segmentation. This highlighted Nmap's utility in actively testing and validating security controls from a Blue Team perspective.

Why Integrate Nmap? The "Force Multiplier" Effect

No single security tool is a silver bullet; each has its strengths and weaknesses. The real power in a security operations or auditing toolkit comes from tool integration – making different tools work together. By combining the strengths of Nmap with other specialized tools, security professionals can gain deeper insights, improve workflow efficiency, and achieve a more comprehensive understanding of their security posture. Nmap often serves as the initial reconnaissance and discovery engine, with its findings feeding into other tools for more specialized analysis or action.

Introducing a Conceptual Security Toolchain

Think of a common workflow or "toolchain":

1. Nmap: Used for network discovery, port scanning, service identification, OS fingerprinting, and initial vulnerability checks (via NSE). It tells you what's there and what might be weak.
2. Wireshark: When Nmap finds something unusual or you need to understand specific network conversations in detail, Wireshark (a packet analyzer) allows you to look at the raw packets.
3. Snort/Suricata: These are Intrusion Detection/Prevention Systems (IDS/IPS). Nmap's findings can help you write more effective IDS rules to detect or block malicious activity targeting services Nmap identified.
4. Nessus/OpenVAS: These are dedicated vulnerability scanners. Nmap can provide them with a list of live hosts and open ports to make their scans more targeted and efficient. Nmap's versatile output formats, especially XML (-oX), are key to enabling these integrations, as XML is easily parsed by other scripts and tools.

Nmap and Wireshark: From Scan to Packet Analysis

Nmap tells you what ports are open and what services might be running; Wireshark can show you the actual conversation happening on those ports.

How Nmap Findings Guide Wireshark Analysis

Nmap scans often reveal interesting situations that warrant a deeper look at the packet level:

• Unusual Open Ports/Services: If Nmap discovers an unexpected open port or a service banner that seems out of place (e.g., a non-standard service on a common port), you can use Wireshark to capture traffic to/from that specific port on that host. This allows you to see what kind of data is being exchanged and understand the protocol in use, even if Nmap's service detection was unsure.
• Investigating NSE Script Behavior: If an NSE script reports an interesting finding (e.g., a vuln script indicates a potential vulnerability, or a discovery script elicits a strange response), you might want to see the exact packets the script sent and what the server sent back. Capturing this interaction with Wireshark can provide valuable context.
• Troubleshooting Nmap Scans: If Nmap has trouble (e.g., ports consistently show as filtered, OS detection is unreliable for a specific host), capturing the scan traffic with Wireshark can help diagnose the issue. You can see if Nmap's probes are actually reaching the target, if firewalls are dropping them, or if responses are malformed.

Practical Workflow Example

1. Run Nmap: Perform your Nmap scan (e.g., sudo nmap -sS -sV <target_IP>). Let's say it identifies an open TCP port 12345 with an "unknown" service.
2. Start Wireshark Capture: Launch Wireshark and start a capture, ideally filtering for the target IP and port to reduce noise (e.g., Wireshark display filter: ip.addr == <target_IP> and tcp.port == 12345).
3. Interact or Re-Scan: While Wireshark is capturing, you could re-run a very targeted Nmap scan against that specific port (sudo nmap -sV -p 12345 <target_IP>), or use Ncat (ncat <target_IP> 12345) to try and interact with the service manually.
4. Analyze in Wireshark: Stop the capture and examine the packets. Look at the TCP handshake (if any), the data payloads, and any error messages. This can help identify the protocol, understand why Nmap couldn't fully classify it, or see if the service is behaving suspiciously.

No Direct Nmap Command for Wireshark

Nmap and Wireshark are separate tools. The integration is a manual process of using Nmap's output to inform where and what to look for with Wireshark. Having both tools readily available and understanding how to use Wireshark's capture and display filters is key. Being able to follow TCP/UDP streams in Wireshark is particularly helpful when analyzing traffic related to Nmap findings.

Nmap and Snort/Suricata: Informing Intrusion Detection

Nmap can identify potential weaknesses or policy violations; IDS/IPS like Snort or Suricata can then be configured to monitor for attempts to exploit or interact with them.

How Nmap Findings Improve IDS Rules

Nmap scans provide valuable intelligence that can be directly translated into more effective IDS rules:

• Monitoring Vulnerable Services: If Nmap (perhaps via an NSE vuln script or by identifying an old software version with -sV) discovers a known vulnerable service on a specific host, you can write a Snort/Suricata rule to specifically alert on or block traffic patterns associated with known exploits for that vulnerability, targeting that host and port.
• Detecting Policy Violations: If Nmap identifies an unauthorized service running on a host (e.g., a Telnet server on a critical machine), you can create an IDS rule to alert any time traffic is seen going to or from that prohibited service on that machine.
• Baseline Deviations: If Nmap (via Ndiff) detects a new, unexpected service appearing on a host, you can quickly add an IDS rule to monitor traffic to this new service until it can be investigated and either authorized or removed.

Developing IDS Rules for Reconnaissance Detection (with caveats)

While sophisticated attackers use techniques to evade standard IDS signatures for Nmap scans (like timing adjustments, fragmentation, decoys), you can still create IDS rules to detect more basic or noisy scanning activity. Different Nmap scan types (SYN, FIN, Xmas, Null, UDP scans) have distinct packet characteristics. IDS rules can be written to look for:

• A large number of SYN packets to different ports on one host from a single source (indicative of a SYN scan).
• TCP packets with unusual flag combinations (FIN only, Null, Xmas).
• Excessive ICMP unreachable messages coming from your network (could indicate a UDP scan against closed ports). It's a cat-and-mouse game, but having some rules can catch less sophisticated probes.

Basic Snort Rule Syntax Example

A basic Snort rule has a header and options. Nmap's output provides the details needed for the header (action, protocol, source/destination IPs, ports).

# Nmap found Apache Struts CVE-2017-5638 potentially on 192.168.1.100
alert tcp $EXTERNAL_NET any -> 192.168.1.100 80 (msg:"EXPLOIT ATTEMPT Apache Struts CVE-2017-5638"; flow:to_server,established; content:"Content-Type"; content:"multipart/form-data"; content:"%{(#_=multipart/form-data"; nocase; reference:cve,2017-5638; classtype:web-application-attack; sid:1000001; rev:1;)

In this conceptual example, 192.168.1.100 and port 80 would come from Nmap's findings. The content matches are specific to the exploit. Nmap tells you what is running and where; you then use that to craft targeted IDS rules. The lab for this lecture could involve students analyzing Nmap XML output and then writing a pseudo-Snort rule based on an identified service or vulnerability.

Nmap and Nessus/OpenVAS: Complementary Vulnerability Scanning

Nmap has NSE vuln scripts, but dedicated vulnerability scanners offer more comprehensive capabilities. The tools are complementary.

Distinguishing Nmap's NSE from Dedicated Scanners

Nmap with NSE vuln scripts:

• Excellent for quick checks for specific, often network-exploitable, known vulnerabilities.
• Highly flexible and scriptable, allowing for customized checks.
• Provides a network-centric view, often identifying issues based on how services respond over the network.
• Generally performs unauthenticated (black-box) network checks.

Nessus / OpenVAS (Dedicated Vulnerability Scanners):

• Maintain extensive, commercially curated (Nessus) or community-driven (OpenVAS) databases of tens of thousands of vulnerabilities.
• Perform more in-depth checks, including application-level flaws, misconfigurations, and patch levels.
• Can perform authenticated (credentialed) scans, allowing them to log into systems and check for local vulnerabilities and patch status much more accurately.
• Provide detailed reporting, risk scoring, and remediation advice. Nmap's vuln scripts are useful for targeted checks, while dedicated scanners provide broader, deeper coverage.

How Nmap Complements Dedicated Scanners

Nmap can significantly improve the efficiency and effectiveness of dedicated vulnerability scanners:

1. Target Scoping: Run Nmap first to perform host discovery (-sn) and identify live systems across the target network ranges.
2. Port/Service Identification: Use Nmap to determine which ports are open and what services are running (-sS -sV).
3. Feeding Targets to Nessus/OpenVAS: Export the list of live hosts and open ports from Nmap (e.g., from -oG or parsed -oX output). Import this list into Nessus/OpenVAS as the target list. This ensures the dedicated scanner doesn't waste time probing dead hosts or ports Nmap already knows are closed/filtered, making its scans faster and more focused on active services.

Verification and Deeper Investigation

Nmap can also be used to:

• Verify Findings: If Nessus/OpenVAS reports a network-level vulnerability, you might use a specific Nmap NSE script or manual Ncat interaction to get a second opinion or understand the context better.
• Investigate Specific Ports: If a vulnerability scanner flags a particular port or service as problematic, you can use Nmap for deeper enumeration of that specific service (using relevant NSE discovery scripts) to gather more information before attempting remediation.

The synergy is clear: Nmap provides the initial map of the terrain and identifies points of interest. Nessus/OpenVAS then perform a more exhaustive geological survey for valuable (or dangerous) resources at those points. Using them together provides a more robust vulnerability management process.

Lab

Students take XML output from a scan in Scenario 3 (Web/Cloud). They write a basic Snort/Suricata rule to detect scanning activity or connection attempts to a "vulnerable" port/service identified by Nmap. (Optionally, provide sample PCAPs for Wireshark analysis related to Nmap findings).

Nmap/Short Course/Lab 11