What is SSL Sniffing and How to Avoid It?

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As the Internet of Things becomes more secure, cybercriminals are forced to come up with new methods to intercept and steal sensitive data. They usually take advantage of existing cybersecurity tools and try to trick users into trusting them. So this article will help you learn what is an SSL Sniffing attempt . It will also show you how to protect your SSL connection from it. But first, let's define what a TLS/SSL proxy is to complete the job.

Table of contents

What is a TLS/SSL termination proxy?
What is SSL Sniffing?
How does SSL Sniffing work?
How to Avoid SSL Sniffing?
How to Prevent SSL Sniffing?
What is a TLS/SSL termination proxy?
A TLS/SSL termination proxy is a proxy server that is used by an organization to intercept and process incoming TLS/SSL connections, decrypt the TLS/SSL, and then pass the unencrypted request to one of its highly secure servers, such as Apache HTTP Server, Nginx, or HAProxy.

The purpose of using a proxy server to terminate TLS/SSL is to reduce the load on an organization's main servers. But before implementing this proxy, the organization must ensure that its network is so secure that it does not need to encrypt session data for its users.

Unfortunately, attackers have learned to exploit the TLS/SSL termination proxy capabilities to eavesdrop on secure SSL connections. Now they can easily intercept messages exchanged within it.

What is SSL Sniffing?
SSL sniffing is a malicious cyber attack where a TLS/SSL termination mobile app development service proxy acts as a MitM proxy, intercepting a secure SSL connection .

Why MitM (man-in-the-middle)? Because a proxy is by definition a third party “man in the middle”. The proxy connects to the server, and then the client connects to the proxy.

How does SSL Sniffing work?
You may already know that SSL certificates prevent MitM attacks . How is it that a MitM can intervene and eavesdrop on an SSL connection?




When sniffing an SSL connection, the MitM proxy acts as an untrusted CA. The MitM proxy dynamically generates SSL certificates for any hostname required to establish an SSL connection. For example, if a browser wants to connect to, the MitM proxy will generate an SSL certificate for sign it as an independent CA.

By intentionally posing as a separate CA, a malicious MitM proxy exploits this capability and attempts to intercept a trusted SSL connection. So when a browser attempts to connect to a web server, the MitM proxy intervenes by issuing and signing its own certificate. So while the MitM proxy receives the server's original SSL certificate, the browser receives a fake SSL certificate issued by the MitM proxy.

But here comes the crucial part of the SSL Sniffing attempt:

The browser thinks it's connecting to a server, but it's actually connecting to a MitM proxy. Here's where the sniffing comes in: for sniffing to work, the browser must accept this proxy as a real, trusted CA.

If the user ignores all security warnings and accepts the fake SSL certificate and the MitM proxy CA as trusted, he will successfully connect to the MitM proxy, initiate SSL Sniffing, and the SSL connection will become insecure.