Equip your developers with relevant knowledge on authentication-related vulnerabilities! Our library of 650+ exercises covers the most popular programming languages and security topics, using both guided tutorials and more difficult challenges. We make it easy for you to find, assign, and track your developers’ progress on Avatao’s interactive authentication training modules.

authentication vulnerabilities

What is Authentication?

At its core, authentication is the process of identity verification. It ensures that a user, website, or other entity trying to access certain resources is who they claim to be. The goal is to make sure a malicious actor is not impersonating a trusted source and accessing content they shouldn’t be.

While there are many ways of authenticating entities, a common and well-known method is with a username or ID and a more private bit of information, often a password, digital signature, or even face or voice scans.

Types of authentication

Passwords may be the most common way to authenticate one’s identity, but it is far from the most secure.

Single-factor/primary authentication

The simplest and most-common (and therefore least secure) method of authentication.

This could include username and password, a PIN code, or any situation in which only a single factor or credential is used for verification.

Two-Factor Authentication (2FA)

This type of authentication uses the same username and password as single-factor authentication, but then adds a second piece of identifying information from outside the system. Some examples include a verification code sent to a smartphone, an answer to a secret question, or an additional one-time password – but there are many more!

Multi-Factor Authentication (MFA)

The most secure form of authentication. It uses a combination of several factors that are independent from the system where the primary authentication takes place. These factors can include additional passwords, one-time passwords, biometric data, device-based confirmation, or even location information – and those are just a few examples!

Single Sign-On (SSO) authentication

This authentication scheme allows a user to access multiple applications by logging in with a single ID and password.

For example, by logging in to Gmail, you are automatically authenticated to many other Google services, such as YouTube, Google Analytics, and other Google apps.

Most frequent attack vectors

For a variety of reasons, the occurrence of authentication-related vulnerabilities – also known as broken authentication – is on the rise. Let’s check some potential attack vectors and a few ways to mitigate them:

Brute force attacks

One of the oldest tricks in the book, this is essentially automated trial and error. An attacker tries many character combinations and lengths in a password field – at lightning speed, thanks to the power of computers – until they get a successful response from the backend.

Mitigation techniques: high entropy passwords, MFA, captcha, limiting the number of login attempts


Dictionary attack

A type of brute force attack in which the attacker uses a “dictionary” of values for its attempts. For example, they might use a file containing the most frequently used passwords, or an even more sophisticated file of potentially meaningful terms for a given target, such as family member names or birthdays. 

Mitigation techniques: don’t use common passwords or passwords containing personal information others can easily find


Session management attacks

Without appropriate safeguards, there are many ways to hijack a verified session ID, which a malicious actor can then use to impersonate another user’s identity. This could include stealing a session cookie when a user forgets to log out of a website before walking away from their device, or getting the session ID from the URL via an unsecured wifi connection.

Mitigation techniques: always log out of websites before leaving your device unattended, give a new session ID to a user after they log in

Phishing attacks

Attackers can easily gain access to user profiles by sending emails in which they pretend to be a trusted entity, and then tricking the victim into sharing sensitive data.

Mitigation techniques: never open suspicious emails!

Real-life examples of authentication related vulnerabilities

Check out the 50+ authentication-related exercises on our platform in which you can learn about several attack vectors and how to fix them in different programming languages:

  • Strengthening authentication with ASP.NET Core Identity (C#)
  • Authentication and authorization (Kotlin)
  • Broken authentication (Python)
  • Custom authentication with Spring Security (Java)
  • Broken 2FA
  • .. and many more!
broken authentication exercises

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