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Written by: Laura Fitzgerald

Head of Brand and Digital Experience

Replay attacks pose a significant threat to a system’s security. They operate maliciously or fraudulently by repeating or delaying user communication. Their simplicity is their strength, allowing them to intercept sensitive data, steal session keys, or impersonate a legitimate user by exploiting valid sessions even after the original session ends. This can lead to severe consequences such as unauthorized access, information theft, or financial loss, underscoring the urgent need for effective countermeasures.

Organizations can bolster their security and support robust authentication processes by harnessing advanced biometric analysis, integrating AI, and, most importantly, leveraging the power of voice authentication. This technology is crucial in mitigating replay attacks and provides a seamless user verification method.

What is a Replay Attack?

A replay attack is a network attack in which an attacker captures a valid network transmission and retransmits it later. The main objective is to trick the system into accepting the retransmission of the data as legitimate. Common symptoms indicating that a system may be under a replay attack include unusual, repeated requests for authentication, suspicious patterns of network traffic, and incoming requests that exactly match previously recorded data patterns.

Clients using Point-to-Point Protocol (PPP) to authenticate and sign on are susceptible to replay attacks when using Password Authentication Protocol (PAP) to validate their identity. However, replay attacks can also include the use of voice. 

6 Different Types of Replay Attacks 

Online banking is an area with a simple example of replay attacks. They can occur by capturing a transaction message with an encrypted digital token or signature. Then, the process is repeated to transfer funds without the user’s consent. Replay attacks involve successfully intercepting a user’s data. 

Another example of a replay attack could be when a company staff member asks for a financial transfer by sending an encrypted message to the financial administrator. An attacker eavesdrops on this message, captures it, and can now resend it. A replay attack could also involve unauthorized users capturing and replaying credit card information to make fraudulent purchases on behalf of individuals without them authorizing the transaction. With the correct information, an attacker can retransmit a user’s login details to gain unauthorized access to their online accounts, making them tricky and challenging to catch in real-time. 

Here are several types and examples of replay attacks to be aware of:

  1. Basic Replay Attack
    This is where an attacker intercepts a legitimate message and retransmits it to the original recipient or another entity. Chainlink gives a simple example of replay attacks that can be seen in online banking. When a user initiates a transaction, such as transferring funds to another user, the transaction’s validity is often authenticated using a digital token or signature.
  2. Replay Attack with Modified Data
    Like a basic replay attack, the attacker modifies certain parts of the captured message before resending it. Modern cars use keyless entry systems where the key fob communicates wirelessly with the vehicle. When a user presses the unlock button on the key fob, it sends a signal to the car, unlocking the doors. In 2019, researchers demonstrated a practical replay attack on Tesla Model S vehicles. They captured and modified the communication between the key fob and the car, which allowed them to unlock the car and start its engine without the owner’s key fob. This attack exploited vulnerabilities in the car’s keyless entry system by capturing the key fob’s signal and replaying it with slight modifications to bypass security protocols.
  3. Delayed Replay Attack
    This is when an attacker delays the retransmission of the intercepted message, potentially causing confusion or incorrect system behavior. An example could be replay attacks in stock trading, which can be used to manipulate market data. An attacker might intercept valid buy or sell orders and retransmit them to execute fraudulent trades. This can create false market signals, leading to stock price manipulation. Implementing unique transaction identifiers and timestamps can help mitigate these risks by ensuring each transaction is valid only once and within a specific time frame​​.
  4. Pre-play Attack
    In a pre-play attack, an attacker predicts a legitimate message before sending and sends their version first. In authentication protocols, an attacker sends a guessed correct token before the legitimate user does. Pre-play attacks are particularly concerning for contactless payments, which rely on quick and convenient transactions without requiring a PIN or signature for low-value purchases. These attacks exploit some contactless payment systems’ lack of robust verification methods. For example, attackers can modify transaction data between the card and the payment terminal, making it possible to approve fraudulent transactions without proper authorization.​
  5. Reflection Attack
    The attacker sends a request to a server that causes the server to send the response back to itself or a different server in a loop, often exhausting resources. Using a service request that the server responds to by querying another server creates a loop that congests network resources. In 2022, a notable example of a reflection attack involved the TP240PhoneHome reflection/amplification DDoS attack vector. This attack exploited vulnerabilities in the TP-240 DVR service, allowing attackers to generate an amplification ratio of up to 2,200,288,816:1. This means that a single spoofed request could generate an immense amount of traffic, potentially resulting in up to 2.5 TB of attack traffic from a single command. This attack affected various sectors, including broadband ISPs and financial institutions, causing significant disruption.​
  6. Duplicate Attack
    The attacker duplicates a message multiple times to flood the target system. For example, they send multiple copies of a payment request, which can cause numerous transactions. A notable example of a “duplicate attack” in recent news involves a political maneuver during the 2024 Washington governor’s race. This incident featured two individuals named Robert Ferguson, who filed to run against the current Attorney General, Bob Ferguson, creating confusion among voters. This move allegedly intended to mislead voters and split the vote to prevent the real Bob Ferguson from advancing in the primary election. This tactic was denounced as an attack on the electoral system and democracy. Eventually, both duplicate candidates withdrew their names from the ballot after legal pressure and public scrutiny.​

How to Mitigate a Replay Attack?

Mitigating replay attacks involves using cryptographic techniques, protocols, and secure practices. The most effective countermeasures include employing encryption protocols with unique session keys and implementing time stamps or sequence numbers in messages. 

The Importance of Voice Authentication in Mitigating Replay Attacks

Today, voice authentication in contact centers is critical to confirming valid customers, improving customer experience, and safeguarding customer accounts. However, efficient customer authentication can be tricky and requires an optimized IVR experience to identify and mitigate the risks of replay attacks. Here are four advantages of voice authentication that can add to a powerful defense against replay attacks and enhance overall cybersecurity.

  1. Strong Authentication
    Voice authentication integrated within call centers supports security remotely and helps call center operations identify callers based on personalized information.
  2. User Convenience
    The Pindrop voice authentication technology allows entities to verify their customers through natural conversation, eliminating the need to answer multiple security questions or enter PINs. This streamlines the authentication process, making it quicker and more convenient for customers​. 
  3. Replay Attack Prevention
    Various layers help ensure that replay attacks can’t get through call centers. Controlling the number of requests per user (i.e., not allowing repeat messages), allowing for mutual authentication (a security process in which both parties in a communication verify each other’s identity), implementing private security keys, session tokens, challenge-response protocols, timestamps, and a nonce (a unique value used only once) can all help.
  4. Enhanced Multi-Factor Authentication (MFA)
    Voice can be combined with other authentication methods (like passwords or facial recognition) to create a more secure multi-factor authentication process. Each person’s voice has unique characteristics, such as pitch, tone, and speaking style, making it difficult to replicate or forge. Pindrop’s 2024 Voice Intelligence and Security Report covers how to navigate the evolving threats in voice security and equip your business with robust tools to combat fraudsters and authenticate your customers effectively.

Pindrop® Solutions That Can Help Detect Replay Attacks

Pindrop’s innovative Deep Voice®technologies offer tailored solutions to help combat replay attacks.

A recent example of a replay attack is the September 2023 data breach at MGM Resorts International. In this specific scenario, the cybercriminals employed Vishing (voice phishing) to manipulate MGM Resorts International’s IT team into resetting Okta single sign-on passwords. Pindrop solutions offer a multi-factor platform that helps protect against a broad spectrum of attacks, including Vishing. Specifically for Vishing, Pindrop offers solutions like spoofing detection based on phone number, voice authentication, and liveness detection

These features can be instrumental in rejecting impostors’ voices, detecting repeat fraudsters, or identifying indicators of manipulations in the victim’s voice, such as deepfake or replay attacks. Two top 20 banks saw 20x ROI by leveraging Pindrop solutions to reduce fraud and improve customer experience and operation costs.