Certified - CompTIA Network +

Network traffic is at constant risk while in transit. Even if endpoints are secure, the data moving between them can be intercepted, altered, or redirected by attackers. This threatens both the confidentiality and the integrity of communication. Many modern attacks don’t require breaking into a system—they simply require standing in the path of the traffic. Once in that position, attackers can observe, manipulate, or reroute data before it reaches its destination. Protecting the flow of traffic is a foundational element of network defense and is regularly tested on the Network Plus exam.
This episode focuses on interception-based attacks: on-path techniques, also known as man-in-the-middle attacks, and DNS poisoning attacks that redirect users to malicious destinations. These attacks are designed to break trust—tricking devices or users into thinking they’re communicating with a legitimate endpoint, when in reality, they’re being deceived. Understanding how these threats are executed—and how to recognize, prevent, and respond to them—is critical for protecting the network and the users who rely on it.
An on-path attack, traditionally known as a man-in-the-middle attack, occurs when an attacker positions themselves between two communicating parties—such as a user and a server—and intercepts or alters the communication without either side being aware. The attacker might relay messages unchanged or modify them to insert malicious commands or extract sensitive information. This kind of attack relies on the attacker’s ability to appear trusted to both endpoints. On the exam, you’ll need to understand how these attacks operate and how trust can be exploited at the network level.
Attackers can establish on-path positions in several ways. One common technique is ARP spoofing, where the attacker sends forged Address Resolution Protocol messages to a switch or host, making it believe the attacker’s MAC address belongs to the gateway or target device. Another method is the deployment of rogue access points—malicious wireless networks that mimic legitimate ones to lure users into connecting. Attackers may also compromise switches or routers to silently observe or manipulate traffic. The exam may ask how attackers establish visibility between endpoints and which protocols can be abused.
HTTPS downgrade and SSL stripping attacks are examples of how encryption can be bypassed or disabled during on-path attacks. In these cases, the attacker intercepts HTTPS traffic and forces a downgrade to HTTP by modifying requests and responses in transit. Without encryption, credentials, session cookies, and personal data are exposed to interception. These attacks rely on users not noticing that a secure connection has become insecure. To stop them, encryption must be enforced, not optional. On the exam, you’ll be expected to identify downgrade techniques and recommend encryption policies to block them.
Credential theft is a primary goal of many on-path attacks. Once in position, attackers can observe login forms, capture usernames and passwords, and reuse those credentials to access systems directly. In more advanced cases, attackers may steal authentication tokens or session cookies and replay them to gain unauthorized access. This makes the compromise difficult to detect, as it appears to come from a legitimate user. Session replay and credential capture are common topics on the exam, particularly in questions involving web authentication and proxy interception.
Session hijacking is a related but distinct tactic in which an attacker takes over an active session between a client and server. This can be done by stealing the session ID, often stored in a cookie, or by injecting themselves into an active stream and impersonating the client. If a user is authenticated but not using secure cookies or encrypted transport, an attacker can seize control of the session and act on the user’s behalf. You’ll need to identify session hijacking techniques and know how to detect and prevent them on the exam.
DNS poisoning, also known as DNS spoofing, is an attack where the attacker sends false DNS responses to redirect users to malicious servers. These responses can redirect a user attempting to visit a legitimate website—like their bank—to a fake site controlled by the attacker. Once redirected, users may unknowingly provide login credentials or download malware. DNS poisoning can occur locally on a device, within a compromised router, or upstream at a vulnerable DNS server. The exam may test your understanding of DNS poisoning as a form of misdirection that undermines trust in domain name resolution.
DNS cache poisoning is a technique used to inject false entries into a DNS server’s cache. When the server receives a query, the attacker quickly sends a fake response with incorrect data, hoping the server accepts it before a legitimate reply arrives. If successful, the poisoned record is cached and served to all future clients until the TTL—time to live—expires. This allows attackers to hijack traffic on a wide scale. On the exam, expect questions that ask how DNS responses are trusted and how cache poisoning manipulates that trust.
The consequences of DNS poisoning are far-reaching. Victims can be directed to phishing sites that steal credentials, download malware from attacker-controlled servers, or lose access to legitimate services. Because the DNS response appears valid, these redirections are hard to detect without close DNS traffic inspection or logging. In some cases, the redirection may last for hours or days. On the exam, be prepared to evaluate attack symptoms and recognize DNS poisoning as a root cause of unexpected traffic redirection.
DNS-related vulnerabilities arise from a lack of response validation, lack of encryption, and trust in the first answer received. Standard DNS queries and responses are unencrypted, allowing attackers to spoof replies. Because DNS uses UDP, there’s no handshake to validate sender authenticity. If a source IP can be forged and the timing is right, poisoning is possible. Many servers also don’t check for unexpected responses, increasing exposure. For the exam, you’ll need to understand how these vulnerabilities are exploited and how to counter them through secure DNS practices.
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Defending against on-path attacks starts with strong encryption. All traffic—especially traffic containing credentials or sensitive data—should be encrypted using protocols like HTTPS, TLS, and SSH. Relying on optional encryption leaves the door open for downgrade attacks, so enforcement tools like HTTP Strict Transport Security, or HSTS, are essential. HSTS ensures that browsers always use HTTPS for specific domains, blocking attempts to redirect users to unencrypted versions of a site. Certificates must also be validated properly; expired, self-signed, or mismatched certificates should trigger alerts. On the exam, expect to select encryption-based solutions to counter on-path threats.
DNSSEC, or Domain Name System Security Extensions, is a defense against DNS poisoning. DNSSEC uses digital signatures to verify the authenticity of DNS records. When a client queries a domain, it also receives a signature that can be validated using a chain of trust. If the record has been tampered with, the signature won’t match and the response will be rejected. This adds integrity checking to a protocol that normally lacks it. On the exam, you may be asked how DNSSEC protects against cache poisoning and how it fits into a secure name resolution strategy.
Good network configuration practices are key to preventing attackers from inserting themselves into communication paths. Static ARP entries can prevent spoofing on critical systems by ensuring that known MAC addresses are always associated with expected IPs. Monitoring for unauthorized DHCP or DNS servers on the network can prevent rogue devices from handing out malicious configurations. Infrastructure devices should be hardened—this includes disabling unnecessary services, securing management interfaces, and applying regular updates. The exam may ask which practices reduce the risk of redirection or traffic interception at the local level.
Monitoring and detection provide visibility into attacks as they happen. Network administrators can analyze ARP tables for unexpected mappings, monitor DNS traffic for abnormal response behavior, or use intrusion detection systems to catch signs of packet tampering. IDS tools may be configured to alert when traffic patterns suggest a man-in-the-middle setup or when spoofed DNS responses are detected. Unusual name resolution behavior, such as multiple redirects or uncommon top-level domains, can also be signs of manipulation. On the exam, expect questions about how to recognize these anomalies using monitoring tools.
Client-side protections add another layer of defense. Users should be trained to verify URLs and certificate warnings in browsers. Systems should be configured to reject expired or invalid certificates automatically. Operating systems and browsers should remain updated to patch protocol-level weaknesses. Users should also avoid untrusted or public Wi-Fi networks when accessing sensitive systems, or use VPNs to ensure encrypted tunnels when remote. On the exam, be prepared to recommend endpoint or user-based mitigations that help protect against on-path attacks and DNS hijacking.
DNS logging is a valuable resource for detecting poisoning attempts. Logs can show which domains were queried, what responses were returned, and whether any mismatches occurred between expected and actual IP addresses. Alerting tools can flag uncommon domains or repeated queries to known malicious infrastructure. This is particularly useful for identifying command-and-control communication during malware infections or lateral movement attempts. On the exam, you’ll need to know how DNS logs support forensic analysis and early threat detection in compromised environments.
Exam scenarios often present symptoms of interception—such as redirected traffic, credential theft, or mixed HTTP and HTTPS sessions. You’ll need to recognize these as signs of on-path or DNS-based compromise. You’ll also be expected to identify the protocols used, the weak points exploited, and the most effective countermeasures. That includes knowing which DNS settings support validation, how ARP spoofing is detected, and how encryption protocols are applied to protect confidentiality and integrity across the network.
To summarize, interception attacks like on-path manipulation and DNS poisoning are designed to break the trust users place in their networks. These threats hijack data, redirect traffic, and exploit visibility gaps to steal credentials, inject malware, or conduct surveillance. Defending against them requires layered strategies: encrypting traffic, validating name resolution, hardening devices, and monitoring behavior. Whether you’re preparing for the Network Plus exam or defending a production environment, your understanding of how attackers manipulate traffic—and how to stop them—will be critical to maintaining secure communication.
To conclude Episode One Hundred Forty-Eight, interception threats expose the fragility of trust on modern networks. From ARP manipulation to DNS redirection, attackers look for ways to place themselves invisibly between endpoints. Preventing this requires a security-first mindset, one that prioritizes encryption, validation, and continuous monitoring. These concepts are a cornerstone of both exam success and real-world network defense, and your ability to recognize and respond to them makes all the difference in securing data in motion.