In the context of the CompTIA PenTest+ certification, an On-path attack—formerly and commonly referred to as a Man-in-the-Middle (MITM) attack—is a critical exploit where an attacker secretly positions themselves between two communicating parties. The objective is to intercept, relay, and potential…In the context of the CompTIA PenTest+ certification, an On-path attack—formerly and commonly referred to as a Man-in-the-Middle (MITM) attack—is a critical exploit where an attacker secretly positions themselves between two communicating parties. The objective is to intercept, relay, and potentially alter the data flowing between a client and a server without either party suspecting interference. This attack vector severely compromises both the confidentiality and integrity of network traffic.
To successfully execute an On-path attack during an engagement, a penetration tester must first manipulate network protocols to redirect traffic through their control. On local networks (Layer 2), ARP Poisoning is the predominant technique. By flooding the network with forged ARP messages, the attacker links their MAC address with the IP address of a legitimate gateway, forcing victim traffic to route through the attacker’s machine. In wireless environments, an Evil Twin attack serves a similar purpose by mimicking a legitimate access point.
Once the attacker creates this bridge, they can employ tools such as Ettercap, Bettercap, Responder, or mitmproxy. These tools allow for passive sniffing to harvest credentials or active manipulation to inject malicious code. A specific, high-value technique is SSL Stripping, which forces a victim's browser to downgrade from a secure HTTPS connection to unencrypted HTTP, rendering encryption useless and exposing sensitive data like passwords and session tokens in cleartext.
For the PenTest+ exam, understanding remediation is just as vital as execution. Defenses include enforcing strict encryption standards like TLS 1.3 and utilizing HTTP Strict Transport Security (HSTS) to prevent protocol downgrades. Network-level defenses involve implementing Dynamic ARP Inspection (DAI) on switches and using Virtual Private Networks (VPNs) to tunnel traffic securely, preventing local attackers from deciphering the intercepted data streams.
On-path Attacks (MITM) - CompTIA PenTest+ Guide
Introduction and Importance On-path attacks, traditionally known as Man-in-the-Middle (MITM) attacks, are a staple concept in the CompTIA PenTest+ curriculum. They are critical to understand because they demonstrate how an attacker can actively intercept, modify, or relay communications between two parties without their consent. Understanding this attack vector is essential for identifying vulnerabilities in unencrypted protocols (like HTTP, Telnet, and FTP) and weaknesses in Local Area Network (LAN) configurations.
What is an On-path Attack? An On-path attack occurs when an attacker secretly relays and possibly alters the communication between two parties who believe they are directly communicating with each other. The attacker sits logically 'in the middle' of the network connection, gaining the ability to read confidential data (like credentials) or inject malicious data.
How it Works The mechanics of an On-path attack usually involve two phases: Interception and Decryption/Manipulation.
1. Gaining the Position (Interception): The attacker must force traffic to flow through their machine. Common methods include: - ARP Spoofing/Poisoning: The attacker floods the LAN with forged ARP packets, associating their MAC address with the IP address of the default gateway. This causes victims to send traffic to the attacker instead of the router. - LLMNR/NBT-NS Poisoning: Using tools like Responder to answer local name resolution requests when DNS fails. - Evil Twin: Creating a rogue Wi-Fi access point to intercept wireless traffic.
2. Handling the Data: Once the traffic is intercepted, the attacker may use tools to strip encryption (SSL Stripping) to view HTTPS traffic as HTTP, capture session cookies, or replay authentication hashes.
Tools to Know for the Exam Be familiar with these tools for On-path scenarios: - Ettercap & Bettercap: Suites used for ARP spoofing and packet manipulation. - Responder: specific to LLMNR/NBT-NS poisoning. - Wireshark: Used to analyze the traffic or detect the attack (e.g., seeing duplicate IP addresses with different MACs). - Burp Suite/OWASP ZAP: Proxies used to intercept and modify web traffic specifically.
Exam Tips: Answering Questions on On-path attacks (MITM) 1. Identify the 'How': If an exam question asks how an attacker on a local subnet is capturing traffic intended for the internet, the answer is almost always related to ARP Spoofing or ARP Poisoning.
2. Recognize the Symptoms: Look for scenario clues such as: - 'Certificate warnings' (indicating an intercepting proxy). - 'Duplicate MAC addresses' in logs. - 'High network latency' (due to the attacker processing traffic).
3. Remediation & Prevention: For remediation questions, focus on specific defenses: - Dynamic ARP Inspection (DAI) and DHCP Snooping on switches preventing ARP poisoning. - HSTS (HTTP Strict Transport Security) prevents SSL Stripping. - VPNs encrypt traffic, rendering interception useless.
4. Terminology: CompTIA uses 'On-path' and 'Man-in-the-Middle' interchangeably. Do not get confused; they refer to the same concept.