ICMP Timestamp Scan (`-PP`) with Nmap

Introduction

Network scanning is a critical aspect of cybersecurity, allowing security professionals and network administrators to map, monitor, and secure their infrastructure. Among various scanning techniques, the ICMP Timestamp Scan (-PP) is one of the lesser-known but valuable methods for gathering intelligence about a target system. This article explores the ICMP Timestamp Scan (-PP) using Nmap, explaining its purpose, how it works, and its implications for network security.

What is ICMP Timestamp Scan?

ICMP (Internet Control Message Protocol) provides various functionalities beyond simple echo requests (ping). One of these functionalities is the ICMP Timestamp Request and Reply mechanism. The ICMP Timestamp Scan (-PP) in Nmap leverages this functionality to determine whether a target is online and to analyze the system’s clock settings.

This type of scan can be useful for:

• Checking system availability: Identifying live hosts on a network.
• Measuring network latency: Determining response times of hosts.
• Fingerprinting system clocks: Gathering system clock data to identify time zone differences and potential operating system details.

Unlike traditional ICMP Echo Requests (ping), which are often blocked by firewalls, ICMP Timestamp Requests may still be allowed, making this scan a useful alternative for host discovery.

How ICMP Timestamp Requests Work

The ICMP Timestamp Request (Type 13) and ICMP Timestamp Reply (Type 14) messages are part of the ICMP protocol suite. These messages function as follows:

1. The scanning system sends an ICMP Timestamp Request packet to the target.
2. If the target host is reachable and responds, it sends an ICMP Timestamp Reply containing:
   • Originate Timestamp: The time when the request was sent from the scanner.
   • Receive Timestamp: The time when the request was received by the target.
   • Transmit Timestamp: The time when the reply is sent back to the scanner.
3. The scanner calculates round-trip time (RTT) and compares timestamps to determine the system clock settings and possible time zone information.

By analyzing these values, security professionals can infer potential time drift issues, OS fingerprints, and network latency.

Using ICMP Timestamp Scan (-PP) in Nmap

Nmap is a powerful network scanning tool that includes the -PP flag for ICMP Timestamp Scanning. To use this scan, simply run the following command:

nmap -PP <target>

Example Usage

1. Scanning a single target:

   nmap -PP 192.168.1.1
   

   This command sends an ICMP Timestamp Request to 192.168.1.1 and waits for a reply.

2. Scanning a range of IPs:

   nmap -PP 192.168.1.0/24
   

   This scans all hosts in the 192.168.1.0/24 subnet using ICMP Timestamp Requests.

3. Combining with other scan techniques:

   nmap -PP -sP 192.168.1.0/24
   

   This combines ICMP Timestamp Scan (-PP) with a Ping Sweep (-sP), increasing the chances of detecting active hosts.

4. Evading firewall restrictions:

   nmap -PP --spoof-mac 00:11:22:33:44:55 192.168.1.1
   

   This command spoofs the MAC address to attempt bypassing security mechanisms.

Interpreting Scan Results

After running an ICMP Timestamp Scan, Nmap provides output similar to the following:

Starting Nmap 7.94 ( https://nmap.org ) at 2024-03-26 10:15 UTC
Nmap scan report for 192.168.1.1
Host is up (0.0045s latency).

• “Host is up”: Confirms that the system responded to the ICMP Timestamp Request.
• Latency (0.0045s): Measures the response time, which can be useful for network troubleshooting.

If the scan does not return results, it could indicate:

• The host is offline.
• The host’s firewall blocks ICMP Timestamp Requests.
• The network is filtering ICMP traffic.

Security Implications of ICMP Timestamp Requests

While ICMP Timestamp Requests are useful for network discovery, they also introduce security risks. Some key concerns include:

1. Potential for Host Enumeration

   • Attackers can use -PP scans to identify live hosts in a network.
   • This information may aid in further reconnaissance and targeted attacks.

2. Time-Based Attacks

   • If an attacker determines the system clock settings, they can exploit timestamp-based vulnerabilities.
   • Time drift information may help identify system types or configurations.

3. Firewall Evasion

   • Since many networks block ICMP Echo Requests but allow ICMP Timestamp Requests, attackers may use this method to bypass simple security policies.

Mitigation Strategies

To reduce risks associated with ICMP Timestamp Requests:

• Disable ICMP Timestamp Replies unless necessary.
• Use firewall rules to block ICMP Timestamp Requests at the perimeter.
• Enable logging and monitoring for unexpected ICMP activity.
• Use network security tools (e.g., IDS/IPS) to detect and mitigate scanning attempts.

On Linux systems, disabling ICMP Timestamp Responses can be done with:

sysctl -w net.ipv4.icmp_ignore_bogus_error_responses=1

Or by adding the following to /etc/sysctl.conf:

net.ipv4.icmp_ignore_bogus_error_responses = 1

When to Use ICMP Timestamp Scanning

ICMP Timestamp Scanning can be beneficial in several scenarios:

• Network Administration: Checking network latency and host availability.
• Security Testing: Identifying vulnerable systems in penetration testing.
• Network Troubleshooting: Diagnosing connectivity issues between devices.

However, ethical considerations and legal compliance must always be observed. Unauthorized scanning of networks without proper permission may violate laws and corporate policies.

Conclusion

The ICMP Timestamp Scan (-PP) with Nmap is a useful technique for discovering hosts and analyzing network response times. While often overlooked, it can provide valuable information for security professionals and network administrators. However, due to the security risks associated with ICMP Timestamp Replies, organizations should implement proper security measures to prevent unauthorized reconnaissance.

By understanding and effectively utilizing ICMP Timestamp Scanning, network professionals can enhance both their offensive and defensive security strategies.