> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/web/authentication/broken-2fa-logic.md).
# Broken 2FA Logic
Broken 2FA Logic notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### 2FA Broken Logic
The application introduces two-factor authentication: / After login/password, a **code 2FA** is sent by **email**. / We have:
* Our credentials: `wiener:peter`
* The victim's username: `carlos`
Access to **mail server** to receive 2FA codes
#### Observed Operation
1. After the first login step, the application sends a 2FA code by email.
2. The second step (`/login2`) checks this code.
3. The user for which the 2FA is valid is determined via the **`verify`** cookie.
Example of a request to the second step:
```http
GET /login2 HTTP/2
Host: 0a7500ab0376700f81a18e2c00f200a8.web-security-academy.net
Cookie: session=cNFHPofUz1wxXQpsZZN7yIiKQklG1Ygd; verify=carlos
```
Here, we force the `verify` cookie to `carlos` so that the 2FA check is done on the victim's account.
#### Brute-Forcing the 2FA Code
1. The 2FA validation request is sent to **Intruder** (or equivalent) by targeting the request containing:
```bash
mfa-code=XXXXX
```
* The **payload** is configured to test all possible combinations of code, from `0000` to `9999` (i.e. 10,000 values).
We use the cookie:
```bash
verify=carlos
```
* for all code tests to be performed on the account of **carlos**.
* In the settings, a \*\* filter condition\*\* is added to the response to ignore those that contain the message:
* `Incorrect security code`
1. We're launching the brutal force attack.
2. Among the responses, we find the one that no longer contains the error message and returns a \*\* HTTP code 302\*\* (direction). / → This answer corresponds to **code 2FA correct** on behalf of **carlos**.
---
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