How to Prevent and Detect Packet Sniffing Attacks

August 11, 2022 | By IANS Research

Packet sniffing is one method hackers employ to gain access into networks as trusted users—first to perform reconnaissance, then to inflict lasting damage. This piece details what a packet sniffing attack is, how it works, common techniques used, challenges associated with these attacks and how to protect your organization from packet sniffing attacks. 

How Packet Sniffing Attacks Work

In principle, packet sniffers aren’t a hazard. In fact, they’re an important part of most companies’ cybersecurity stack. Legitimate packet sniffing is the process of looking into data throughout your organization. 

As computers share information, access networks or use the internet, packets of data are exchanged. These data packets contain information such as who the user is, what they’re doing, what networks and sites are used, as well as text from messages, login information, IP addresses and various other data. In an organization, “good” packet sniffing software will compile these packages into a single storage point, where your IT team can sift through and look at user data. This keeps the organization safe and ensures employees are staying on task. Alternatively, you might only compile certain types of packets that are deemed higher risk. 

Packet sniffing is a great way to keep your organization safe, but it can also be used by hackers to steal information. A malicious packet sniffing attack employs the same tactics as a legitimate one, but the data goes directly to the hacker instead of your secure storage space. In this type of attack, the hacker is accessing packets filled with critical and confidential information. To put it simply, a hacker is intercepting and looking through data within your network. 

Types of Packet Sniffing Attacks 

How is a packet sniffing attack carried out? There are two different ways — either through an active or passive packet sniffing attack. 

Active Packet Sniffing Attacks 

An active packet sniffing attack is one in which a hacker injects a new protocol into your network or a user’s computer. From there, legitimate packets and traffic will get re-routed to the hacker’s storage device. It might involve attacks like: 

  • Spoofing attacks 
  • DHCP attacks 
  • DNS poisoning

Passive Packet Sniffing Attacks 

In a passive packet sniffing attack, the hacker takes a less direct route by monitoring your hub, or network, and looking at packets as they pass by. 

For this type of sniffing attack, hackers simply look over your shoulder and read the same packets your security team sees. Essentially, they are stealing admin access to the hub, which is much harder to detect, since there is no direct injection or traceable attack. 


READ: How to Build a Proactive Threat Hunting Strategy 


Targets for Packet Sniffing Attacks 

When it comes to targets of these attacks, organizational size varies. Larger organizations are more attractive because most have large networks with ample amounts of transferable data. Additionally, the financial rewards for stealing packets of data from larger organizations are far greater than with smaller firms.  

Once a packet sniffing attack is launched, hackers can continue to gather information from your organization until they have enough to direct a second more lethal attack. This might include a targeted spear-phishing attack, malware injection or logging into network devices to attack from the inside. 

How Packet Sniffing Attacks Work 

In many cases, packet sniffing attacks are only the first phase of a security breach. They’re used to gather a lot of information about a company before rolling out a second or even third phase of attacks. To better understand how a hacker might attack a business with a sniffing attack, here are three steps a hacker might use. 

Step 1: Launch the Sniffing Attack  

The first stage of the attack is to implement the sniffing attack technique the hacker prefers. This might involve injecting malicious code into a computer, spoofing access to a network hub, spoofing MAC addresses or altering a computer’s DNS cache. 

Regardless of the style used, the hacker will discreetly implement the attack to avoid detection. 

Step 2: Collect Data 

From there, the hacker can spend any period of time waiting around and collecting data. There are cases where hackers wait months or even years to collect enough important information to level an organization. 

In other examples, hackers are looking for quick money, so they might only sift through packets for a few days before moving to the next stage. 

Step 3: Launch a Malicious Attack 

The final stage is the most dangerous. With the information gathered, the hacker can decide what the next steps are, but they will almost always implement a second, more malicious attack. 

Attackers might use logins to get into your network and use ransomware to lock up your system. Alternatively, they might threaten to sell trade secrets to your competitors or leak sensitive information to the public to extort the organization. In addition, the stolen packets contain a lot of personal information that can be used to initiate a highly specific, targeted phishing attack. 

The bottom line is the hacker is likely looking to get compensation somehow, and this second step is a good way for them to get started. 


READ: Ransomware: Prevention and Response Tactics 


Common Packet Sniffing Techniques 

There are many packet sniffing techniques and styles hackers might use. Some of the most common examples are: 

  • MAC spoofing. The hacker compiles a list of MAC addresses that are connected through the network. They will then spoof or fake one of the legitimate MAC addresses to gain access to the network. Think of this attack like a hacker putting on a disguise that looks like one of your employees and pretending to be them. 
  • MAC flooding. They might also flood your network with a lot of different MAC addresses. This causes your network switch to get overloaded and stop working for long enough for the hacker to get in. 
  • DNS cache poisoning/evil twin attack. A hacker will navigate around your company’s DNS protocol, allowing them to redirect traffic from different users. As a user tries to go to a harmless site, the hacker can navigate them to a malicious one and download malware onto their device. The re-routed site is referred to as the “evil twin,” since it responds to the DNS request before the legitimate site can. 

Challenges with Packet Sniffing Response

Detection is the most significant challenge packet sniffing attacks pose to security teams. It’s difficult to spot the hacker because they might look like an authorized user or even a system administrator. Once you find the sniffing breach, it’s easy to boot attackers from the network, but initial discovery is hard, and understanding the scope of the hack is even harder. 

Another challenging aspect is determining the level of damage that can be done by a single attack. It’s possible for a hacker to steal enough information to shut down your operation. 

How to Prevent Packet Sniffing Attacks   

Packet sniffing attacks have become commonplace since inexpensive network packet analyzers are widely available to hackers. Best practices to help guard against sniffing attacks and keep both networks and your organization safe include: 

Use a Secured Network 

  • Unsecured networks are much easier for hackers to attack in general. A firewall will help prevent hackers from accessing your secured network, and anti-virus software will scan for active sniffing attacks. 
  • Make sure your network requires a password, and monitor which users access the network. These steps will secure your network.

Use a VPN 

  • Using a VPN makes it harder for hackers to locate and access packets that are sent. A VPN will fully encrypt the data end-to-end, and it will bounce all packets between a few different secured servers before going to your network. This requires the hacker to also get through the different secured servers. 
  • Avoiding unsecured public Wi-fi access while using encryption will make a sniffing attack difficult to carry out. 

READ: Remote Access Security: VPN vs VDI 


Use Sniffer Detection Tools 

  • Use a sniffing detection application so your server will constantly look for active and even passive sniffing attacks. It will detect most of the attacks mentioned earlier before alerting system admins and kicking out the hacker. 
  • Several sniffer detection tools are available. Take the time to research and find the right tool for your organization. 

Packet sniffing attacks can be a serious security threat, with the potential to impact business operations in any size organization. At a minimum, sensitive data can be stolen and used against your organization, putting your business and your employees at risk. Understanding how packet sniffing attacks work, why they’re so damaging and how to prevent them is important. Keep in mind: Prevention is easier than detection. Ensure your network is secured from outside intrusion and your cybersecurity stack is robust. 

Although reasonable efforts will be made to ensure the completeness and accuracy of the information contained in our blog posts, no liability can be accepted by IANS or our Faculty members for the results of any actions taken by individuals or firms in connection with such information, opinions, or advice. 


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