What is a replay attack and how to prevent it

What is a replay attack and how to prevent it

Cyber security threats are widespread these days, and you are prone to lose your sensitive information or money. They exist in many forms, and one typical example is the replay attack. This is where criminal intercepts and ‘replays’ a secure network communication to misdirect the receiver into doing whatever they want.

The biggest danger with this attack is that the hacker does not require advanced skills to decrypt the message after intercepting the network. In fact, it can be successful by just resending the entire thing without adding anything else. So, if you’re not following cybersecurity best practices for escaping cyber attacks, you can become a become easily.

How does a replay attack work?

Person A sends a login request to a website, which is verified and granted access. However, person B hacks and intercepts the request without the authority of person A or the website. The hacker does not even need to know the request's content but can just replay it. Sadly, the website will see that person A is trying to log in again, and the request will succeed.

Cybercriminals can eavesdrop on data exchanges transmitted through networks, also known as packet sniffing. Then, they replay the intercepted data in the same form – typically an email, session ID, or a message. In most cases, these attacks are used to collect usernames and passwords or steal money.

But how is the replay attack successful yet passwords are encrypted? Usually, passwords are scrambled with a private key only known by the site. However, this is not sufficient defense to prevent a replay attack. The hacker will only need to replay the authentication, provided it is successful, and they don't even need to use the password. This is also known as the 'pass-the-hash attack'.

Typically, passwords are hashed and salted to prevent this from happening. Salting is the process of adding random and unique characters known only to the site to every password before hashing. Unfortunately, this practice is less secure as sometimes websites use the same salt for each website.

Is it possible to prevent a replay attack?

As mentioned above, a secure and encrypted password is not enough to prevent a replay attack. So, what will you do to stay safe?

  • One-time password (OTP) – This is a good option because you only use it once.
  • Timestamp – Add a timestamp that is only valid for a short period. This will deny the hacker enough time to launch the replay attack.
  • HTTPS protocol – Ensure you only visit websites with an HTTPS security feature to protect your data.
  • Public or free Wi-Fi – Try to avoid public Wi-Fi hotspots in airports, restaurants, libraries, etc., as hackers can exploit the weak security.
  • A virtual private network (VPN) – You should get a trustworthy VPN service to conceal your internet activities from third parties. Also, it will encrypt your connections, preventing hackers from eavesdropping or intercepting your data transmission.

Wrap up

Replay attack may seem subtle, but it is pretty dangerous. It does not require advanced skills to execute, and you can lose your sensitive data or money even if you have a strong password. Thankfully, specific measures can help you prevent the attack, like using a one-time password, adding timestamps, or connecting to a VPN.