Prevent a Replay Attack from Disrupting Your Business Operations

Image of a VHS tape.
Replay attacks have nothing to do with rewinding a VHS tape!

Have you been curious about replay attacks? A replay attack occurs when a cyberattacker intercepts a message and delays or replaces it with another message. This is very similar to a ‘man-in-the-middle’ (MiTM) attack. However, in a replay attack, the interceptor doesn’t need to decrypt the data packets.

In effect, a replay attack is much easier to use than an MiTM attack. A cyberattacker also doesn’t need much technical knowledge to leverage one to their advantage. In essence, replay attacks are more accessible than MiTM attacks, so they’re more dangerous.

In this article, I’ll delve into what replay attacks are and how you can protect yourself from them. First, let’s start with a definition!

What Is a Replay Attack?

A replay attack is a network-based attack where a cyberattacker intercepts traffic between network nodes and conducts packet sniffing. Attackers often look for session IDs and passwords from end users accessing server-based services.

A replay attack requires access to the target network. Cybercriminals often conduct it as a physical-based attack on site. That said, attackers can also use devices like LAN turtles to relay data offsite. Cyberattackers typically install these LAN turtles between a target’s network interface card and the rest of the network. 

When onsite, a cyberattacker may often use a redirect attack or ARP poisoning attack. This way, they can route traffic to the attacker without adding more hardware to the network.

Once the attacker has access to a target user’s traffic messages and server, for instance, the packets get sniffed and rerouted to the destination. Once a cyberattacker receives something valuable, like a user’s username and password, they can use this information even if the user is offline.

The goal of a replay attack is similar to an MiTM attack: to steal user information or credentials. After that, attackers can access core business platforms for further exploitation. The difference is that MiTM attacks use Wi-Fi interception to help steal network credentials. In addition, MiTM packet sniffing mostly occurs from outside the network. 

On the other hand, replay attacks usually happen from within the network to help escalate privileges. They also help access segmented areas in the business. You can use traffic encryption protocols with router-based VPNs to ensure even mobile device packets are safe from packet sniffing. 

Now that you know what replay attacks are, let’s take a look at how they can get used against you!

How Can a Replay Attack Affect a Business?

Replay attacks often help a criminal access segmented parts of your business and escalate permissions. To do this, the attacker targets personnel with elevated privileges and little cybersecurity experience. Examples include CEOs or board members that had access to the system when the business was growing. It also includes division leads, project champions, and low-level or new IT administrators. Cyberattackers can also use replay attacks to access server-based platforms or most front-end onsite platforms. 

Once an attacker has all the credentials they need, they could implement malware and perform other evil actions. These include:

  • Implementing ransomware across the network 
  • Accessing intellectual property to sell to others 
  • Destroying or creating fake users; they do this to send “new” employee details to HR for processing access cards to onsite premises

Now, let’s take a look at how you can prevent replay attacks!

How You Can Prevent Replay Attacks

To stop replay attacks from occurring, you can do a few things. First, implement Secure Socket Layer (SSL) or Transport Layer Security (TLS) for all communications with an HTTPS everywhere policy. This will then encrypt your communication, which can reduce the attackers’ ability to sniff out information.

You can also salt hashes with a session ID and timestamp. This way, the attacker can’t use hashes again, as they’re only valid for a certain session ID or timestamp. Furthermore, the attacker won’t reuse the intercepted packets.

In addition, make sure user cookies get removed periodically from browsers. Cookies often contain session IDs. And attackers can use these IDs to pose as you. Even more, an attacker can look at what you’ve been doing on the internet. 

One more thing to consider is to make sure you prevent end users from customizing their browsers. In fact, customization provides attackers with ways to identify users, habits, and future attack vectors. Taking this one step further, some companies try to keep end-user hardware the same for this reason as well. Management may want to use lightweight laptops with screen sizes, resolutions, firmware, and hardware configurations that can also single them out.  

Now you know everything you need to keep your business safe! Let’s wrap up.

Final Thoughts

You can stop replay attacks using basic security measures as part of your operations security (OPSEC) and infrastructure hardening processes. When these measures are in place, an attack on your network will become less likely. 

You should be using HTTPS for everything to encrypt traffic. If possible, consider using routers with VPNs to help encrypt traffic automatically sent from mobile devices. This stops user errors or automatic updates from sending unencrypted traffic through the network. If you combine HTTPS and password salting with a timestamp and session ID, you can effectively stop a replay attack.

Do you have any more questions on replay attacks? Check out the FAQ and Resources sections below!


What is a replay attack?

Replay attacks occur when a message gets intercepted by a cyberattacker on a network, who then delays or replaces it with another message. They do this to steal credentials and access server-side platforms by monitoring an end user’s traffic. This attack doesn’t need much skill to implement as it doesn’t necessarily need decoding; messages are repeated to access platforms. 

How can I prevent replay attacks?

Follow an SSL/TPS/HTTPS everywhere policy. You’ll reduce the likelihood of cyberattackers reusing messages to access server-side platforms. Salt hashes with timestamps and session IDs can also help. Also, ensure users can’t customize their browsers, as this can easily identify them as targets. One last thing you can do is to clear your browser cookies from time to time.

Is a VPN good enough to prevent a replay attack?

No, you should consider implementing timestamps and session IDs with HTTPS everywhere. If you’re using VPNs, use one that has end-point protection to reduce the risk of replay attacks intercepting VPN server communications. Also, ensure your users are clearing browser cookies often.

How do cyberattackers use replay attacks against me?

Replay attacks often help criminals steal credentials from users. Then, the cybercriminals can conduct attacks that require escalated permissions or access to certain platforms like ERP systems. One use could be to help propagate ransomware to mission-critical locations of the business. To mitigate replay attacks, consider using HTTPS, SSL/TPS, and salt hashes with timestamps and session IDs. 

Will using timestamps help prevent a replay attack?

Traffic timestamps stop cybercriminals from replaying credentials. Once the traffic goes out, it can’t get resent and accepted. You should also encrypt your traffic using SSL or TPS and implement an HTTPS everywhere policy. Lastly, use a router that supports automatic VPN connections to prevent accidentally sending any unencrypted data, especially during automatic updates.


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