Authentication Bypass Tricks

Authentication is the front door of any app. And front doors get a LOT of attention from defenders — but they also have a surprising number of ways to sneak past. Let me walk you through the classic auth bypass tricks.

What Is Authentication Bypass?

Simple: getting into an account (or a protected area) WITHOUT the proper credentials. No correct password needed. You find a side door, a logic gap, or a forgotten check. And it's one of the highest-impact things you can report.

The Classic Tricks

1. Response manipulation: The login fails and the server sends back something like {"success": false}. What if you intercept that response and flip it to {"success": true}? On poorly-built apps, the client trusts it and logs you in. 😳

2. The password reset takeover: Reset flows are FULL of bugs. Can you reset someone else's password by changing the email/user in the request? Is the reset token weak or guessable? Does the reset link leak via the Referer header? Tons of opportunities here.

3. OTP/2FA bypass: Is the 6-digit code rate-limited? If not, you can brute-force it. Can you skip the 2FA step entirely by going straight to the post-2FA page? Does the OTP get returned in the API response (yes, this happens 😭)?

4. SQL injection in login: the classic admin' -- (remember post 8?) still works on careless apps.

5. Default/weak credentials: admin/admin, admin/password — embarrassing but it works more than you'd think, especially on forgotten subdomains.

How To Hunt It

1. Map the ENTIRE auth flow: login, signup, reset, 2FA, logout, "remember me"
2. Capture every request and response in Burp
3. At each step ask: what does the app TRUST here? The response? A token? A user-supplied email?
4. Break each trust: flip responses, swap emails in reset requests, brute-force OTPs, skip steps
5. Pay special attention to the password reset flow — it's the buggiest part of most apps

Why It's Top-Tier

Because auth bypass usually means account takeover — the holy grail for impact. If you can get into someone else's account, that's almost always critical/high severity. Big payouts live here.

My Honest Tip

The password reset flow is where I'd spend my time as a beginner. It's complex, it's everywhere, and developers mess it up constantly. Map every single step and question every value. The token, the email field, the link — one of them is usually too trusting.

Next post: race conditions — winning the battle of milliseconds.

Find the side door! 🚪