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What is a replay attack?

Hackers can eavesdrop and intercept your internet traffic and then use it to gain access to your accounts and online profiles. While this might sound like the plot from an action movie, it’s exactly what a replay attack is all about. What are the common methods in replay attacks, and how can you protect yourself?

What is a replay attack?

Table of Contents

Table of Contents

What is a replay attack?

A replay attack is a network attack when an attacker intercepts a network communication between two parties to delay, redirect, or repeat it. Then, the cybercriminal pretends to be one of the legitimate parties and retransmits the traffic to replicate or manipulate the original action.

How does a replay attack work?

To launch a replay attack, criminals must gain access to your network to eavesdrop on your internet data. There are several ways to achieve this, but usually, hackers implant malware on the victim’s device or set up a fake hotspot, which they can control remotely. A replay attack is a more specific type of man-in-the-middle attack, so they share some similarities.

In a replay attack, a hacker intercepts your data and resends the same web request to a server, so it looks like that data is coming from your browser. When the server sends back a response, the hacker will receive it. But what type of data attracts hackers?

  • Session ID (a piece of data that allows a user to be identified on a website).
  • Login credentials and password hash (a method in which a password is turned into an unreadable string of characters).

Let’s say you want to log into your account on social media, internet forums, or any other website. You type your login credentials into a website, and then your browser sends the username and the password hash to the corresponding server. If an attacker intercepts your password hash and session ID, they can initiate a new session and pretend to be you. All of this can be done without the server knowing they’ve been attacked.

Since hackers can resend messages over the network without decrypting them, it’s easy to trick the receiver into thinking this message is authentic.

What are the risks of a replay attack?

A replay attack is particularly dangerous because it doesn’t require superior hacking skills to decode the information captured from the transmission. The attacker can resend the message to the original recipient just as it is, tricking the other party into believing that the query is legitimate.

The essence of a replay attack is to gain unauthorized access to secure systems, leading to data theft or service disruptions. This attack is particularly dangerous in financial systems because replaying transaction messages can result in unauthorized transactions, leading to fraud or manipulation of financial accounts.

Methods of a replay attack

As we’ve just discussed, a replay attack is a dangerous cybersecurity issue that may significantly breach your network’s privacy. So, it’s important to understand that these attacks may come in different disguises, and it is essential to get the gist of the main ones to secure your network correctly. So, let’s explore various techniques hackers use to carry out replay attacks.

Network replay attack

In a network replay attack, the attacker collects bits and pieces of data while sniffing around a network. For example, you enter a password to log into a social media platform. The hacker listens to this data transmission between your device and a server, captures the password, and then resends it to the server. The server trusts the malicious sender and allows access to the network. This technique exploits a system’s security vulnerabilities when the data transmission process between the sender and receiver is not properly encrypted.

Wireless replay attack

In a wireless replay attack, a hacker targets wireless networks (Bluetooth or Wi-Fi) by intercepting and recording data transmission between a wireless device and an access point. The main goal of such an attack is to manipulate wireless communication and make the two points believe the replayed data is authentic. Hackers exploit this vulnerability to gain unauthorized access to networks or disrupt services.

Session replay attack

A session replay attack involves the attacker intercepting network traffic and obtaining unique session tokens or cookies. This information allows them to imitate the legitimate user within a web application or service, giving the attacker unauthorized access to website functions as if they were the user.

HTTP replay attack

During an HTTP replay attack, a hacker captures and resends plain text HTTP requests to the receiver. Bad actors can do this through sniffing, unsecure networks, or installing malware on the victim’s device. This attack is often used against websites that don’t employ secure HTTPS for communications. Typically, this replay attack method aims to gain unauthorized access, carry out session hijacking, or disrupt services.

Examples of a replay attack

For an even better understanding of a replay attack, look at how it exploits different vulnerabilities across various platforms ranging from web applications to communication protocols and hardware.

JWT replay attack

During a JSON web token (JWT) replay attack, an attacker intercepts a JWT authentication token and reuses it to gain unauthorized access to the system. For example, if the attacker captures a JWT during your login process, they can replay this token to impersonate you and access your sensitive data without being detected.

Cookie replay attack

In a cookie replay attack, a threat actor captures a session cookie from a user’s interaction with the web. They may use the obtained data to impersonate the user on the same web application. For instance, suppose a user logs into their bank account, and an attacker intercepts the cookie session. They can then replay this cookie to access the user’s banking account and conduct unauthorized transactions.

Kerberos replay attack

As the name implies, a Kerberos replay attack targets the Kerberos network authentication protocol and occurs when a hacker captures authentication tokens to impersonate a user. For instance, obtaining a ticket-granting ticket (TGT) or a service ticket may allow hackers to access networks or services without authorization.

Nonce replay attack

Nonce in cryptography is used to protect networks from replay attacks. However, if configured poorly, it can cause more damage than good. During a nonce replay attack, an attacker manipulates a nonce to bypass security mechanisms. For example, if they intercept a transaction in a blockchain where the nonce is not implemented correctly, the attacker can attempt to replay transactions and access the network without permission.

HackRF replay attack

In a HackRF replay attack, an intruder uses a hardware platform for radio frequencies (RF) to intercept and retransmit signals to access systems. Think of an attacker using a HackRF device to obtain the signal from a car’s key fob and later replay it to unlock the car without actually having the fob.

SAML replay attack

During a security assertion markup language (SAML) replay attack, a hacker intercepts a valid SAML assertion, captures it, and replays it to get into a system maliciously. A hacker might capture a SAML assertion during a user’s login process to an application and replay it to gain unauthorized access.

Active replay attack vs. passive replay attack: What are the differences?

While the attacker takes direct action against the target during an active replay attack, passive replay attacks only involve monitoring the targeted system. This means that active attacks are more dangerous than passive ones. However, take a look at the differences between the two to get a better grasp of how they work.

Replay attacks can do a lot of damage to individuals and businesses, but with certain measures, it’s possible to fight them. Here are a few ways to enhance your security for replay attack prevention.

Active replay attackPassive replay attack
NatureThe attacker intercepts and actively retransmits messages to gain unauthorized access to the system.The attacker monitors the targeted system and captures data but doesn’t immediately use it.
ObjectiveTo initiate unauthorized transactions, access, or actions by replaying captured data.To gather information for future use, such as passwords or encryption keys.
DetectionEasier to detect due to the immediate hacker’s actions on the system or network.Hard to detect because it involves only monitoring and capturing data.
ImpactImmediate and direct, affecting systems, data integrity, or user access.Indirect, with potential future impacts.
PreventionUse of timestamps, nonce values, session tokens, multi-factor authentication, rotating keys, and monitoring for unusual activity patterns.Encryption, secure network protocols, a VPN, and vigilant monitoring of network traffic.

Ways of preventing a replay attack

  • Adding timestamps on all messages. You can create a timestamp on your server and set it to ignore any requests older than your selected time frame. This means that a server can detect which messages fail to meet your timestamp requirements and then ignore them.
  • Using SSL or TLS. When a website supports SSL or TLS security protocols, all the data traveling between a browser and a server is encrypted. Hackers won’t be able to spy on your session ID and use it to impersonate you.
  • Using one-time passwords. Banks mainly use this method to authenticate their users and prevent criminals from accessing their clients’ accounts.

How to enhance your online security

If you’re experiencing any signs of malware infection, it might be the first warning that someone is eavesdropping on your traffic. While successfully preventing replay attacks depends on your server, there are a few things you can do to improve your cyber hygiene and avoid falling prey to hackers.

  • Don’t connect to unsecured public networks. You can find free Wi-Fi in parks, public transportation, airports, cafes, shopping malls, and many other places. Hackers can set up a fake hotspot, intercept your traffic, and use their knowledge to scam you. Always double-check if the network you’re connecting to is legitimate. And if there’s no way to verify this, ensure you’re using a VPN to encrypt your traffic.
  • Enable two-factor authentication. A password is not enough to protect your accounts and stop cybercriminals. Two-factor authentication adds an extra layer of protection because you have to authenticate yourself using an app, token, or text message.
  • Avoid http websites. While most websites use a security protocol called HTTP, indicating that the data traveling between a user and a server is encrypted, many unsecured websites still rely on HTTP. This protocol is not secure; if you see it, be on your guard. Never input passwords, credit card numbers, or any other sensitive information on http websites because a hacker could steal them without too much effort.
  • Use a VPN. A virtual private network redirects your traffic through an encrypted tunnel, masking your data. Always use a VPN when browsing http websites or connecting to public Wi-Fi, as it mitigates the risk of someone eavesdropping on your data. With one NordVPN account, you can protect up to six devices: laptops, tablets, smartphones, routers, and more.