> For the complete documentation index, see [llms.txt](https://ganesha-hk.gitbook.io/cybersecurity-writeups/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ganesha-hk.gitbook.io/cybersecurity-writeups/port-swigger-authentication-labs/lab-14.md).

# lab-14

## Password Reset Poisoning via Middleware

**Difficulty:** Practitioner

### Lab Description

This lab is vulnerable to password reset poisoning. The user `carlos` will carelessly click on any links in emails he receives.

**Objective:** Log in to Carlos's account.

**Credentials:** `wiener:peter` (emails readable via the exploit server's email client)

### Root Cause

The application is deployed behind a reverse proxy or load balancer. While the `Host` header itself may be protected (e.g. restricted to a predefined domain), middleware components also accept and trust host-override headers such as `X-Forwarded-Host`. The middleware sends the domain from the override header to the backend application rather than the original `Host` header value — and these override headers are fully user-controllable.

If an attacker supplies their own domain via `X-Forwarded-Host`, the backend uses it when constructing the password reset link:

```
https://attacker.com/forgot-password/reset/?token=hxhschsjc
```

When the victim clicks this link, the reset token is sent to the attacker's server, allowing the attacker to reset the victim's password and take over their account.

### Exploitation

1. Go to the forgot-password page and submit `username: wiener`.
2. Intercept the `POST /forgot-password` request and send it to Repeater.
3. Send it once as-is to generate a reset email for `wiener`.
4. Replace the `username` value with `carlos` and add the header `X-Forwarded-Host` with your exploit server URL as the value.
5. Send the request, then go to **Exploit Server → Access Log**.
6. Find the request containing `/forgot-password?temp-forgot-password-token=` and copy Carlos's token.
7. Go to **Exploit Server → Email**, open the reset email for `wiener`, and click the reset link.
8. In the URL, replace `wiener`'s token with Carlos's captured token.
9. Set a new password for Carlos and log in to complete the lab.

### Lesson Learned

* Never trust client-supplied host override headers such as `X-Forwarded-Host` when generating absolute URLs.
* Password reset links and other security-sensitive URLs must always use a predefined, trusted domain stored in server-side configuration.
* Validate or ignore untrusted host-related headers unless they originate from known, trusted infrastructure (e.g. your own reverse proxy).
* Deploy a strict allowlist of accepted hostnames at the web server, reverse proxy, and application layers.
* Audit all functionality that generates absolute URLs to ensure none rely on user-controlled request headers — including middleware-level headers.


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