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Packet Sniffing: Types, Methods, Examples, and Best Practices

20th Sep, 2023
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    Packet Sniffing: Types, Methods, Examples, and Best Practices

    Today we live in a digitalized environment where computers and other devices are continually transferring data over the network in the form of packets. These packets are data segments sent from one computer to another over a network and are involved in almost everything. From browsing the internet to managing the entire database of your organization, packets are transferred constantly over the network. As per benign or malicious purposes (for example by network administrators and cyber criminals respectively) These packets can be captured, modified, and destroyed before they reach their destination. So, to obtain a strong foothold in today's world of cyber security, a firm grasp of fundamental terminologies like packet sniffing is crucial. This article will explain what packet sniffing is, how it is done, different types of packet sniffing, and how to prevent packet sniffing, along with best practices. So, let's get started.

    What is a Packet Sniffing Attack?

    A packet sniffing attack, or simply a sniffing attack, is a cyber-attack that involves intercepting and misusing content (like reading sensitive data) passing through a network in the form of packets. Unencrypted email communications, login passwords, and financial information are common targets for a packet sniffing attack. Besides this, an attacker may also use sniffing tools to hijack packets by injecting malicious code into the packet itself, which executes once it reaches the target device.

    Packet Sniffing Attack

    Credit: Toolbox

    Example of Packet Sniffing Attack

    A good example of a packet sniffing attack is DNS cache poisoning, DNS is the protocol that translates the domains into IP for the understanding of the computer and to avoid unneeded lookup browser stores the IP address of such servers in their cache, in DNS cache poisoning attacker sniffs the request through Burpsuite or other interception tools and modify it to malicious DNS servers and cache stores that in this way the DNS amplification type of attacks can be performed. 

    If that sounds interesting, be sure to check out the CEH Course, where we go over major packet-sniffing techniques along with other hacking techniques.

    Types of Packet Sniffing Attacks

    Generally, there are two types of sniffing attacks, depending upon the tools that are used to carry out the attack.  

    1. Hardware Packet Sniffers

    A hardware packet sniffer is intended to connect to and analyze a network. A hardware packet sniffer can ensure that no packets are lost owing to filtering, routing, or other purposeful or unintentional reasons by inserting directly into the physical network at the proper point. A hardware packet sniffer either stores or transmits the intercepted packets to a collector, which logs the data gathered by the hardware packet sniffer for further analysis. 

    2. Software Packet Sniffers

    Nowadays, the majority of packet sniffers are software-based. While each network interface connected to a network can receive all network traffic that passes across it, most are configured to not do so as it can be used to send malicious code. A software packet sniffer modifies this setting, causing the network interface to receive all network traffic up the stack. For most network adapters, this is known as promiscuous mode. Once in promiscuous mode, a packet sniffer's functionality consists of isolating, reassembling, and recording any software packets that flow through the interface, independent of their destination addresses. All traffic that goes across the physical network interface is collected by software packet sniffers. That traffic is then recorded and utilized.

    How Does Packet Sniffing Work?

    Let us briefly look at how packet sniffing in cyber security is actually carried out at a fundamental level. A network interface card (NIC) is a hardware component in any computer that allows it to connect with a network. Non-addressed traffic is ignored by default by NICs. Sniffing attacks necessitate the use of promiscuous mode on the NICs, which is a mode that allows the NICs to accept all network traffic (more on that later). By carrying out data packet sniffing and decoding the encoded information in data packets, sniffers may listen in on all communication travelling through the NICs. Weak or unencrypted data packets make sniffing attacks much more accessible for hackers. 

    Sniffing can be done in two ways, active or passive.  

    1. Active Sniffing

    Active sniffing attacks employ the use of advanced pieces of hardware known as switches. Unlike hubs that send data to all ports even when it isn't needed, switches send data to specified MAC addresses of computers on a network. Active sniffing attacks are often initiated by injecting Address Resolution Protocols (ARPs) into a network in order to overflow the Switch Content Address Memory (CAM) table. The rerouted traffic to other ports allows the attacker to sniff the traffic from the switch. 

    2. Passive Sniffing

    This type of sniffing is generally carried out at the hub. Unlike active sniffing, the hub may be immediately injected with a sniffer device to simply collect data packets. However, hubs are rarely utilized nowadays, therefore passive sniffing attacks are also rarely recorded.

    How Packet Sniffing Attack Works

    Uses of Packet Sniffing

    We’ve already went over some of the malicious uses of Packet Sniffing, but there are other legitimate uses. Let’s take a quick look at both of the following:

    1. Legal Uses

    Networks are extremely complicated, with different sorts of packets flowing in, out, and across the networked machines. This complication makes it easy for things to go wrong. Packet sniffing tools provide network managers with real-time visibility into what is going on in their networks. These technologies assist them in monitoring network traffic, determining whether everything is functioning well, pinpointing bottlenecks, and providing the information required to troubleshoot problems or detect whether the systems are under malicious attack. Wireshark is one of the most commonly used sniffing tool used for legitimate reasons. 

    2. Illegal Uses

    We've talked about how administrators may utilize packet sniffing techniques to obtain a better knowledge of their networks, diagnose problems, and detect threats. But what happens when a malicious attacker does their own packet sniffing on the organization’s network traffic? Many packets that move across a network can be intercepted and logged by packet sniffers. This opens another point of vulnerability, especially if sensitive data goes across the network in an unencrypted manner. An attacker can enter the network and capture all of the packets that flow across it. This can provide them with access to sensitive information of the company or its network users. 

    Methods Used for Packet Sniffing Attacks

    When carrying out packet sniffing attacks, threat actors can use various methods: 

    1. TCP Session Hijacking

    Session hijacking, also known as Transmission Control Protocol (TCP) session hijacking, involves stealing a web user's session ID and impersonating the authorized user. Once the attacker has obtained the user's session ID, they can easily use it to disguise themselves as that user and do any network-enabled tasks that the user is permitted to perform. 

    2. DNS Poisoning

    DNS poisoning, also known as DNS cache poisoning or DNS spoofing, is an another fraudulent cyberattack in which hackers divert internet traffic to phishing websites. DNS poisoning poses a risk to both individuals and businesses. One of the most serious issues with DNS poisoning is that once a device has been infected, resolving the problem may be difficult since the device may default to the illegitimate site. 

    3. JavaScript Card Sniffing Attacks

    An attacker uses a JavaScript sniffing attack to inject lines of code (i.e., a script) onto a website, which then collects personal information input by users into online forms: often, online payment forms. The most typically targeted user data is credit card information, names, addresses, passwords, and phone numbers. 

    4. Address resolution protocol (ARP) Sniffing

    Hackers often transmit fake ARP messages over a local area network, which is known as ARP poisoning or ARP spoofing. These attacks are intended to redirect traffic away from its intended destination and toward an attacker. The attacker's MAC address is connected to the target's IP address, which only works on ARP-enabled networks. 

    5. DHCP Attack

    A DHCP attack is a type of active packet sniffing example used by attackers to gather and modify sensitive data. DHCP is a client/server protocol that assigns a computer an IP address. Along with the IP address, the DHCP server gives configuration data such as the default gateway and subnet mask. When a DHCP client device boots up, it sends out broadcasting traffic, which may be intercepted and modified via a packet sniffing attack. 

    You can follow our IT Security Certifications to learn more about different methods that are used for packet sniffing.

    Packet Sniffing Attack Prevention [Best Practices]

    It’s no doubt that Packet Sniffing attacks are now more common than ever, and this is largely due to the wide availability of different packet sniffers intended for legitimate use which are later modified by the attackers. However, there are some precautionary measures that you can take which might stop or protect you from falling victim to these sorts of attacks.  

    1. Prevent Using Unsecured Networks

    Because an unsecured network lacks firewall and anti-virus protection, the information transmitted over the network is unencrypted and easily accessible. When consumers expose their devices to insecure Wi-Fi networks, network sniffing attacks can easily be carried out. Attackers use unsecured networks to install packet sniffers, which intercept and read any data sent over the network. An attacker can also monitor network traffic by creating a bogus "free" public Wi-Fi network. 

    2. Start Using VPN to Make Messages Encrypted

    Encryption of data increases security by making it necessary for attackers to decrypt it before it can be used, which isn’t an easy task. All incoming and outgoing communication is encrypted before being shared over a virtual private network or VPN. Any attacker sniffing would be unable to see the websites visited or the data transmitted and received. 

    3. Regularly monitor and scan enterprise networks

    Network administrators of an organization should scan and monitor their networks using bandwidth monitoring or network mapping tools to enhance the network environment and identify sniffing attacks.  

    4. Adopt a sniffer detection application

    Some popular applications that are built to detect sniffing tools on your device include Anti Sniff, Neped, ARP Watch and Snort.  

    5. Before browsing online, look for secure HTTPS protocols

    The URL of encrypted websites start with "HTTPS" (hypertext transfer protocol secure), suggesting that user interaction on those websites is secure and guarantees that data is encrypted before it is transmitted to a server. Websites that begin with "HTTP" cannot provide the same level of security, so to avoid packet sniffing, it is advisable to visit websites that begin with "HTTPS." 

    6. Strengthen your defenses at the endpoint level

    Endpoints such as laptops, PCs, and mobile devices when connected to networks, allow security threats such as packet sniffers to infiltrate easily into the organization’s network. Therefore, a powerful antivirus tool should be used to prevent malware from infecting a system by recognizing anything that shouldn't be on a computer, such as a sniffer. 

    7. Implement an intrusion detection system

    An intrusion detection system (IDS) is software that monitors network traffic for any unusual activity and alerts prospective intruders. It can scan a network or system for harmful activity or policy breaches, and any potentially dangerous behavior or breach is often notified to an administrator or consolidated through a security information and event management (SIEM) system.  

    8. Keep an eye on social engineering tactics

    Social engineering is often widely employed by attackers in order to get the victim into making security mistakes or giving away sensitive information. With respect to sniffing attacks, watch out for emails that seem fake and also avoid clicking on suspicious links, among other things.  

    Tools Used for Packet Sniffing

    Currently, many different network sniffing tools have been developed and are actively being used in the industry. They can be hardware based sniffing devices, or software-based tools. Let’s go over few of the main ones:

     Packet Sniffing Tools

    Credit: Software Testing Help

    1. Wireshark

    Wireshark is a popular open-source, cross-platform network protocol analyzer, or a packet sniffer in other words, that captures packets from a network connection. It is widely used, from home computers to IT industries.

    2. tcpdump

    Another packet analyzer known as tcpdump is run from the command line, as opposed to others having a nice GUI. It may be used to study network traffic by intercepting and displaying packets sent or received by the machine on which it is executing. It is compatible with Linux and other UNIX-like operating systems.

    3. dSniff

    dSniff is a collection of password sniffing and network traffic analysis tools designed to parse various application protocols and extract pertinent data. It can obtain information by analyzing a number of protocols (FTP, Telnet, POP, rLogin, Microsoft SMB, SNMP, IMAP, and so on).

    4. NetworkMiner

    NetworkMiner is usually used as a passive network sniffer/packet capture program to discover operating systems, sessions, hostnames, open ports, and so on without causing any network traffic. NetworkMiner is one of the most widely used network analysis tools for detecting hosts and open ports via packet sniffing. It can also be used offline.

    5. Kismet

    Kismet is a WIDS (wireless intrusion detection) framework and a wireless network and device detector which is often used to carry out wireless packet sniffing attacks. Kismet supports Wi-Fi and Bluetooth interfaces, as well as certain SDR (software defined radio) hardware and other specialized capture hardware.

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    Packet sniffing attack is a serious threat in a society where we are more reliant on networked technology to perform personal and professional tasks. It enables hackers to obtain access to data traffic traveling over a network - and with so much sensitive information transmitted over the internet, protecting against packet sniffing attacks is critical. Sophisticated sniffers may exploit vulnerabilities and potentially breach the network security, putting companies at huge risk. The greatest defense against malicious packet sniffing is to monitor the network landscape on a frequent basis, looking for strange activity or abnormalities. Recently, organizations are investing in advanced artificial intelligence methods to protect their data against sniffing. These solutions can be employed to identify even minor changes in network behavior, which IT managers can rectify instantly.

    If you found this article informative, consider reading a bit about our KnowledgeHut’s CEH Course which goes over industry-leading ethical hacking training to protect your organization against the most sophisticated threats.

    Frequently Asked Questions (FAQs)

    1How do hackers use packet sniffers?

    Sniffing tools are commonly available to download, as most are open-source software for educational or legitimate purposes like we discussed before. But that also means that they can be easily accessed by hackers, who can use them to monitor unencrypted data in packets to uncover what information is being sent or received by the victim. If passwords and authentication tokens are delivered in these packets, they can be intercepted.

    2Are Packet Sniffing and Spoofing Both Same?

    Sniffing is the method by which an attacker gains access to a network and listens in on its traffic. Spoofing is the process of making a false IP address the source of a packet in order to gain some benefit from it.

    3Does VPN prevent packet sniffing?

    Any sniffer attempting to monitor traffic across a VPN will only see scrambled data, rendering it worthless to the hacker, and ultimately preventing packet sniffing.

    4Can packet sniffing be detected?

    Sniffers are usually passive and simply collect data. As a result, sniffers are particularly difficult to detect, especially when operating on a shared Ethernet network. Detecting network sniffers might be difficult, but it is certainly not impossible.

    5What is a sniffer?

    A sniffer is a tool that is used to carry out packet sniffing, either for legitimate or malicious reasons.


    Sulaiman Asif


    Sulaiman Asif is an information security professional with 4+ years of experience in Ethical Hacking and a degree of Master in Information Security, he is an EC- Council CEH Certified and has also been engaged with University of Karachi and Institute of Business Management as a cyber security faculty.

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