An insecure application could expose users and systems to various types of damage. When a malicious party uses vulnerabilities or lack of security features to their advantage to cause damage, it is called an attack. We'll take a look at different types of attacks in this guide so you know what to look for when securing your application.
Active attacks vs passive attacks
Attacks can be divided into two different types: active and passive.
With an active attack, the attacker tries to break into the application directly. There are a variety of ways this could be done, from using a false identity to access sensitive data (masquerade attack) to flooding your server with massive amounts of traffic to make your application unresponsive (denial of service attack).
Active attacks can also be done to data in transit. An attacker could modify your application data before it gets to a user's browser, showing modified information on the site or direct the user to an unintended destination. This is sometimes called modification of messages.
With a passive attack, the attacker tries to collect or learn information from the application but does not affect the application itself.
Imagine someone is eavesdropping on your conversation with friends and family, collecting information about your personal life, who your friends are, and where you hang out. The same thing could be done on your web traffic. An attacker could capture data between the browser and the server collecting usernames & passwords, users' browsing history, and data exchanged.
Defense against attacks
Attackers can directly harm your application or perform a malicious operation on your site without you or your users noticing it. You need mechanisms to detect and protect against attacks.
Unfortunately, there is no single solution to make your application 100% secure. In practice, many security features and techniques are used in layers to prevent or further delay the attack (this is called defense in depth). If your application contains a form, you might check inputs in the browser, then on the server, and finally at the database; you would also use HTTPS to secure the data in transit.
Since many attacks can happen without ever hitting your server, it is sometimes hard to detect if attacks are happening or not. The good news is that web browsers have powerful security features already built in. Follow the next topic "How browser mitigates against attacks" to learn more.