What is eavesdropping?

In cybersecurity, eavesdropping is also known as sniffing or snooping. Both terms refer to similar network security threats. However, as we will see, there are different ways to intercept data. Security teams need measures to protect traffic and block snoopers, whatever techniques they use.

Types of eavesdropping attacks

Eavesdropping attacks target sensitive data during transmission by exploiting weak communication channels. They can occur on wired networks, wireless systems, or physical spaces. Knowing the types of eavesdropping helps businesses build stronger defenses.

Active eavesdropping attacks

In active eavesdropping attacks, threat actors pose as legitimate users or customers to access confidential data flows or conversations.

Attackers leverage information about their targets, such as regular contacts, business activities, and personal data. They know when to send emails or make phone calls to enter conversations and extract information.

Passive eavesdropping attacks

During passive eavesdropping attacks, threat actors remain in the background. They silently monitor emails, phone conversations, video feeds, and file transfers. Attackers do not directly influence data flows, making passive attacks hard to detect.

This type of attack is critical for companies reliant on secure data flows. Unlike active techniques, passive eavesdropping involves silently intercepting network traffic without altering it or interacting with the network. Attackers exploit network vulnerabilities, such as unencrypted communications or weak wireless security, to capture and analyze data. Companies can only mitigate these techniques with targeted cybersecurity measures.

Physical eavesdropping

In this familiar scenario, attackers deploy physical devices to gather audio or visual information. Despite the rise of digital business and cloud computing, companies still use basic surveillance to spy on competitors, and states continue to use bugs to monitor threats.

Companies concerned about surveillance devices can use Technical Security Counter-Measures (TCSM) to sweep environments and detect activity.

Why do eavesdropping attacks occur?

Most eavesdropping attacks occur when users send unencrypted confidential data across unsecured networks.

Encrypted data is hard to intercept and decode. Virtual Private Network connections use 256-bit ciphers to scramble data and protect packet contents from external actors. Without encryption, data travels in its original state, and packets have few protections against unauthorized actors.

Confidential data includes personal or professional data that is highly valuable to organizations and their clients. Employees should always send sensitive information securely, using tools like VPNs, encrypted email, and digital signatures.

Unsecured wireless networks have few protections against eavesdropping, such as firewalls, threat detection systems, and encryption. Hotels, restaurants, and other public places often leave networks unprotected. Employees may not realize this and may use these networks to transmit confidential data.

An eavesdropping attack can also result from phishing activities. Attackers can seed surveillance agents via attachments or fake websites and implant them on target networks via persuasive phishing emails.

Eavesdropping methods

Attackers have many ways to intercept and store data. Some methods target network traffic. Others steal audio or visual feeds. All methods have a similar aim: extracting valuable information to monetize for their gain.

Use this list of the most common eavesdropping attacks to inform your security strategy:

• Packet sniffing. Packet sniffing uses tools called analyzers to intercept and capture data packets. Sniffers can reveal websites visited by users, packet source and destination, or email content. They also gather data about network traffic and transfers. Packet sniffing does not typically involve malware delivery but relies on attackers gaining access to a network. Analyzers can filter and decode packets, often providing sensitive information to attackers for exploitation.
• Man-in-the-Middle attacks. In MITM attacks, attackers place themselves between two nodes in a data transfer of conversation. MITM attacks often exploit unsecured public wi-fi networks. For example, attackers could create fake wifi routers in public places and harvest data from unencrypted connections.
• IP spoofing. Spoofing is an MITM attack type where attackers assign fake IP address headers to data packets. Targets may see IP addresses as legitimate and use fake websites or applications. Attackers can then monitor traffic passing through those sites.
• DNS spoofing. DNS spoofing resembles IP address spoofing. However, in this eavesdropping method, attackers compromise DNS servers and change website records in the DNS cache. Attackers can divert traffic from legitimate sites and extract data without users' knowledge.
• Email hijacking. Eavesdropping attackers also use DNS hijacking to intercept emails before they reach inboxes. Threat actors infiltrate DNS servers and imitate legitimate email destinations. They maintain rogue servers to receive and forward emails, enabling them to extract email data and evade detection.
• Keyloggers. Keyloggers register keystrokes made on user devices. Attackers generally deliver them via malware agents, highlighting the need for advanced network monitoring to detect all eavesdropping attacks.
• VoIP eavesdropping. Voice-over-IP is highly vulnerable to MITM-style eavesdropping attacks. Attackers can imitate SIP traffic used by VoIP services. They can then divert traffic to servers of their choice and record calls made by their victims.
• Physical devices. Physical eavesdropping tools include phone taps, listening posts, hidden microphones, mobile device attacks, and hijacked surveillance cameras.

What are the consequences of an eavesdropping attack?

Businesses need measures to counter eavesdropping as the consequences of losing critical data are often severe.

The main risk associated with eavesdropping attacks is financial loss. Companies routinely transmit credit card and banking information about their accounts and those of clients. Attackers can use this information to withdraw funds.

Attackers may also monetize stolen data via the Dark Web. Markets exist for personally identifiable data (PII) and protected health information (PHI). With a single person's PII retailing for $169 on average, eavesdropping can be a lucrative option for opportunistic cybercriminals.

Data breaches also lead to compensation and regulatory payments. In 2024, the average cost of a data breach reached $4.88 million worldwide and $9.36 million in the USA.

Moreover, eavesdropping attackers often prepare the ground for identity theft and phishing attacks. Attackers use extracted information to build target profiles. These profiles help them run social engineering attacks, leading to further damage.

Companies that fall victim to an eavesdropping attack inevitably suffer reputational harm. Customers expect high data security standards. MITM attacks resulting from practices like using public wi-fi networks create a bad public impression. Customers may take their business elsewhere.

Real-world examples of eavesdropping attacks should convince companies to enhance their cybersecurity.

For example, in 2017, credit rating company Equifax suffered a major data breach. In response, it set up a website to help customers find out whether they were affected. Unfortunately, this website was targeted by DNS spoofing attacks exploiting shared SSL certificates. As a result, criminals diverted millions of worried customers to fake websites, which harvested personal data.

Eventually, Equifax paid a settlement of $575 million and agreed to spend over $1 billion on remedial security work.

How to prevent eavesdropping attacks

Given the harmful consequences described above, companies need robust security controls and policies to prevent eavesdropping attacks. Here are some critical elements of an anti-eavesdropping security strategy.

Apply encryption

Use military-grade encryption to conceal data transferred across the network boundary and within the network. VPNs apply encryption to remote access connections and allow secure off-site working. IP address re-assignment also makes it harder for attackers to identify targets.

Use network segmentation

Network segmentation can be implemented by creating firewall barriers to create secure zones inside your network. Users can only enter segments with the correct permissions and credentials. Segmentation makes it harder to access network traffic flows and limits the harm attackers can do if eavesdropping attacks succeed.

Implement network monitoring

Some eavesdropping attacks rely on packet analyzers or keyloggers that remain in the background and reside on network devices. Network monitoring detects suspicious activity and quarantines malicious agents. Monitoring can also track data flows and deliver alerts about unauthorized data extraction.

Train staff in secure practices

Companies can avoid many MITM attacks by training employees effectively. Enforce strict policies on using public wi-fi networks, including the need for VPNs and anti-malware software. Train staff to spot phishing emails and suspicious phone calls that could be evidence of active eavesdropping attacks.

Regularly update applications

Eavesdroppers often exploit out-of-date applications to access networks and spread malware. Ensure all internet-facing apps have appropriate patches. Pay special attention to security tools like anti-malware scanners to keep threat databases current.

Apply physical access controls

Companies concerned about physical surveillance must secure devices and work environments. Implement key cards or biometrics to control access. Lock sensitive devices away when not in use. Install security cameras to detect infiltrators and scan environments regularly to detect bugs.

Conceal sensitive information with cybersecurity protection

Every organization needs security policies and tools to prevent and handle eavesdroppers. In the modern digital economy, attackers constantly seek private data for sale or other malicious actions. Every company is vulnerable, even small businesses with a handful of clients.

NordLayer can help you counter eavesdropping threats. Our Business VPN provides AES-256 and ChaCha20 encryption for remote connections, reducing risks from public Wi-Fi and man-in-the-middle attacks. Cloud Firewall, Device Posture Security, IP allowlisting, and multiple multi-factor authentication options help establish strong network access control policies and segment network access rights.

Strengthen your security posture and block snoopers with proactive threat prevention, encryption, and robust access controls. Threat prevention capabilities like DNS filtering and web protection stop users from accessing malicious websites. Download Protection ensures every download is scanned for malware, and Deep Packet Inspection (DPI) solutions let organizations restrict the use of unsecure apps, vulnerable ports, and protocols.