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Replay Attacks: What Are They & How To Prevent Them?

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PUREVPNCybersecurityReplay Attacks: What Are They & How To Prevent Them?

In your workplace or your private life, how many times do you communicate with others? How many times have you sent a deeply personal or private document? It could be something as professionally serious as your company’s confidential bid for a tender or a document explaining your entire marketing strategy for an upcoming quarter. Now imagine if someone that wasn’t supposed to see any of this gets access to it.

Think that’s bad? Imagine if that same someone could alter any information while it was being sent and make sure the intended destination received it. In this case, they could have altered the figures in the confidential official bid or changed the allocated budget for the marketing campaign.

This is what a replay attack looks like. The effectiveness of such an attack relies on making both the sender and receiver think that the message was delivered unblemished while a massive change has been made. By the time this change is noticed, the damage has probably already been done.

So, if you’re interested to learn more about what exactly a replay attack is, how it works, real-life examples, and most importantly, how you can prevent it, then read on below: 

replay attack

What is Replay Attack?

In the simplest terms, a replay attack is when an unauthorized party gains access to your network traffic and then resumes sending a communication to the originally intended destination. As a result, the unauthorized party is now acting as the sender and can easily access sensitive information that might be received from the original destination.

In other words, think of this unauthorized party as having the ability to eavesdrop on all your conversations, communication, and digital activity taking place through that particular channel. A Wi-Fi network for example.

Also read: How to secure WiFi Router?

There are numerous implications of such an attack since it can render nearly all your communications online vulnerable. More seriously, it will continue to linger as a constant phantom within your future security protocols since there is no way to know for how long your communications have been compromised.

How Does a Replay Attack Work?

A replay attack, often referred to as a playback attack, is one of the primary types of a Man-In-The-Middle (MITM) attack. The unauthorized party gains access to the communications tunnel between a sender and receiver. The party can then manipulate the traffic being sent to the receiver.

What can this mean? Well, suppose you’re sending someone an encrypted document with vital corporate information, and someone intercepts and alters the document while you forward the document to the intended receiver. 

Naturally, this can have devastating consequences for both the sender and receiver. Not to mention, if not adequately resolved, the unauthorized party can continue to access your network and intercept traffic to gain access to similar vital documents or files whenever they want.

What is the difference between a DDoS Attack and a Replay Attack?

Replay attacks and Distributed Denial of Service (DDoS) attacks are cyberattacks with distinct purposes and targets. The main purpose of a replay attack is to intercept and maliciously retransmit data that has been previously recorded without the consent of the owner. 

Meanwhile, a DDoS attack sends a target device or network with malicious traffic or requests, rendering it unavailable to users. 

The replay attacker selects a user he wants to impersonate to gain unauthorized access. In contrast, DDoS attackers target Internet websites, networks, or infrastructure. 

What is a Replay Attack in Blockchain?

In blockchain, when your network upgrades or experiences a hard fork, for example, from Bitcoin Cash (BCH) to Bitcoin (BTC), your blockchain splits into two separate networks. 

The old and new ones have their rules and transactions. Replay attacker captures valid transactions from your one old chain and replays it to the new one with malicious content. 

With this, attackers can easily access your account and use it for double spending or unauthorized transfers as users take the transaction as their own without confirming. 

What Are Replay Attacks on RFID?

Suppose a workplace uses RFID (Radio Frequency Identification) badges for access. Each worker has an RFID badge that carries a unique identifier. When an employee approaches the doorway, they present their badge to an RFID reader, which verifies their identity and approves access.

A replay attacker with malicious intent wants to enter the workplace. What they do is observe an employee presenting their RFID badge to the reader. 

The attacker, using specialized equipment, intercepts and records the data transmitted between the employee’s badge and the RFID reader. This recorded data includes the unique identifier on the badge.

Later, the attacker enters the office building and replays the recorded information from the intercepted RFID transaction to the reader. 

The RFID reader, unable to detect the difference between the original and replayed data, grants the attacker access to the building, allowing them to enter and potentially commit unauthorized activities.

Where Are Replay Attacks Used?

Replay attacks are used mostly where there is a record or history of data. Here are some examples of areas where you should be aware of replay attacks:

  • In network communications through data packets or traffic.
  • In the authentication system, through login processes, by replicating session cookies.
  • In blockchain transactions, during a network fork or upgrade.
  • In wireless protocol, by replaying wireless signals to gain access to WiFi.
  • In access control through RFID-based access or biometrics data.
  • In payment systems that require NFC or RFID-based payments.
  • A remote control system, like unlocking a car through the key fob.

All these systems use unique passwords and identification numbers to allow access to their system. For instance, in network security, replay attacks can compromise data integrity, while in access control systems, they can lead to unauthorized entry.

Ways to Prevent Replay Attacks

At this point, it is safe to assume that you will have realized the dire severity of such an attack and just how costly and dangerous it can be for both your infrastructure as well as virtually all your communications, internal and external.

So, now that you know how big of a deal it is, what can you do about it? That’s where things get a little chummier since if you take the proper precautions and implement them effectively, chances are that you won’t have to deal with such an attack, to begin with. Hence, here’s everything you can do to make sure you never fall prey to a replay attack:

Have An Intrusion Detection System In Place

How do you make sure that no one can simply intrude into your house? You set up an intruder alert system, right? Think the same for your digital communications. An Intrusion Detection System (IDS) is explicitly designed to ensure that no unwanted parties can access or alter the communications you have on your networks. It has a relatively simple operating mechanism as it is meant to trigger an alert almost instantaneously after it detects a network breach.

Moreover, you can take the extra step and have a Security Information and Event Management (SIEM) system in place. It acts as a complementary feature to the IDS as it collects vital information about the unauthorized party that tried to gain access to your network traffic. This is important because of the data it can help you collect, such as what kind of methodology was used. As you may have guessed, this kind of information can prove immensely vital in coming up with future replay attack prevention plans.

Have An Incident Response Plan In Place

A trusted indicator of a company’s preparedness for such an attack lies in how well aware are its employees about their roles in such a scenario. An Incident Response Plan (IRP) is meant to ensure that everyone responsible for preventing and dealing with a replay attack knows precisely what they’re supposed to do.

In addition to increasing both the effectiveness and efficiency of such a plan, it is incredibly beneficial in limiting the damage a replay attack can have. You can limit the severity while also ensuring that the plan can come into effect the moment your IDS detects an attack.

However, just how effective your IRP is, depends on how well trained your staff is, in addition to just how meticulous your plan is. The slightest hint of ambiguity can provide the unauthorized party behind the replay attack with the window of opportunity they need to infiltrate your network successfully. 

Have A Security Breach Response Team In Place

Think of this as an extension of the IRP mentioned above. There’s an old saying that even the strongest chain is only as strong as its weakest link. Needless to say, human negligence might very well be the most vulnerable part of your organization’s plan against any possible replay attacks.

The Incident Response Team (IRT) needs to be appropriately trained, skilled, and motivated to ensure they can carry out your IRP as effectively and efficiently as possible. This means having people with the right set of skills and experience in place.

Often, most companies tend to go for third-party IRTs that specialize in ensuring that no network falls prey to a replay attack. While it is a standard industry practice, you do not necessarily have to follow it to the letter as you can have your internal staff dedicated to it. Such teams within an organization are known as Computer Security Incident Response Team (CSIRT), which specializes in preventing incidents like data or network breaches.

Have A Data Backup In Place

This is more of a preparation for the worst scenario, but you’d be surprised at how little of a headache you might have to deal with if all your sensitive data is appropriately backed up. This means creating a remote data backup of vital information that you can fall back on if a network breach is detected.

This will guarantee that any data loss is minimal while also allowing you to identify where and how any crucial data has been altered. There are different ways companies and organizations create data storage. This ranges from simply copy-pasting their entire data to having a detailed Disaster Recovery (DR). Each of these solutions has its distinct pros and cons in addition to varying expenses.

Get A Reliable VPN

What if you had a tool that could not only encrypt all your incoming and outgoing traffic. Using their own protocols, a VPN, provided that it is a really good VPN, can essentially keep you safe from most replay attacks since it will foolproof your network traffic from being altered in any way while in transit. The network tunnel they create allows you to change your IP address, spoof your location online, and, you guessed it, helps you add another layer of anonymity to all your internet traffic.

Have A Replay Attack Recovery Plan In Place

Simply preventing a replay attack is not enough. While it is ideal to stop the attack from happening at all, the next best thing is to limit the damage it can do to your system. To wit, you need to have a recovery plan in place that a company can follow immediately after thwarting a replay attack.

The most common step that most companies take at this point is to conduct a thorough audit of nearly all their files, in addition to any files and documents they may have sent or received during this time. Afterward, companies usually format all data they suspect of being compromised while restoring them via remote backup.

Simultaneously, most companies initiate the process to find out where the attack originated and what improvements need to be made within their current plan to improve their replay attack prevention techniques further.

Have A Regular Penetration Testing Schedule In Place

Of course, the best way to judge whether your organization, as well as the several plans you have in place to prevent any kind of replay attack, is to keep testing yourself against yourself. Penetration testing has long been considered a highly effective way to identify any gaps or vulnerabilities in your system, so you can fix them before someone exploits them.

Think of these tests as a mock attack that helps test your organization’s preparedness against a replay attack. Ideally, it would help run these mock attacks each time you make a significant change or addition to your company’s hardware or software.

Properly Catalogue All Company IT Assets

This might not be the first thing you think about when it comes to preventing replay attacks, but it can go a long way in ensuring you never have to face such an attack in the first place. Having all your IT devices properly cataloged can help you identify which resources need what kind of protection in case of a replay attack. Moreover, such an audit is crucial in helping you maintain a real-time update of what kind of devices you have connected to your network, what kind of vulnerabilities they might have, and which resources need to be decommissioned and replaced.

Recent Replay Attacks To Know About

The most recent and perhaps the most ominous example of a replay attack has been on the ZigBee Devices for their Internet-of-Things applications. ZigBee has long been a pioneer when it comes to creating applications that utilize IoT mechanisms. However, this has also made them a target for several replay attacks that have affected their devices exponentially, owing to both the software and hardware involved.

The good thing is that ZigBee has yet to face a significant setback since their current plans to thwart such attacks have been successful. Some of their devices that have been attacked include Phillips Hue bulbs, their Xbee S1 and S2C modules, in addition to several network adapters.

Some countermeasures that ZigBee has come up with include in-built mechanisms in each device that would maximize the effectiveness of ZigBe’s replay attack prevention plans.

Some Final Words

Sometimes, even foolproof systems can be rendered fallible owing to a simple mistake. More appropriately, a mistake that could have easily been avoided to begin with. It might seem a little too cynical, but you’d be surprised at just how true this holds. Most replay attack prevention plans fail because the people behind these plans failed to consider minute details.

When it comes to replay attacks or any other man-in-the-middle attacks, the devil is in the details. No detail can be too trivial to ignore, no issue too small to matter. Having the right tool can often help you a lot more than you might realize.

Frequently Asked Questions (FAQs):

Here are some other questions you might have if you’re interested in knowing more about Replay Attacks:

Is there a difference between session replay attacks and regular replay attacks?

No, it’s just another name for a replay attack. Most replay attacks allow a potential hacker to intercept your outgoing and incoming communications. The thing that makes replay attacks so compelling is that it is so subtle that the victims usually don’t realize that they’ve been a victim.

What are the most common network traffic packets captured and used in a replay attack?

By far, the most common traffic packets captured and used in replay attacks are the Authentication ones. You can probably guess why since these packets allow the third party to successfully pass themselves off as the original sender to the receiver.

Does using IPSec provide any additional protection against session replay attacks?

Yes, sort of. A VPN that uses IPSec in addition to some form of Asymmetric encryption ensures that all your outgoing and incoming traffic is adequately encrypted, thus insulating you from any replay attacks. However, there is a catch. At this point, your VPN provider is the one that has control of the secure tunnel that keeps you protected against a replay attack. So, make sure the VPN provider you go for is both trustable and has an encryption protocol that guarantees maximum anonymity for you online.


Yasir Nawaz


September 5, 2023


10 months ago

Yasir Nawaz enjoys writing on issues related to cybersecurity, digital privacy, and online streaming. A firm advocate of digital equality and freedom of access throughout the web, he believes no piece of consumable information should be restricted online. When he’s not busy writing on such immensely important issues, he finds solace in chess, reading, and staring into the abyss in his best Luke Skywalker impression.

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