> 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-access-control-labs/lab-6.md).

# lab-6

## User ID Controlled by Request Parameter

**Difficulty:** Apprentice

### Lab Description

This lab has a horizontal privilege escalation vulnerability on the user account page. The application uses a user-controlled URL parameter to determine which account to display, and does not validate the session against it.

**Objective:** Obtain the API key for the user `carlos` and submit it as the solution.

**Credentials:** `wiener:peter`

### Solution

**Step 1 — Identify the vulnerable parameter**

Log in as `wiener:peter` and capture the requests in Burp. Navigate to the account page and observe the URL:

```
GET /my-account?id=wiener
```

The application uses the `id` parameter to determine which account to load. Send this request to Repeater.

**Step 2 — Confirm the session is not validated**

In Repeater, remove the session cookie entirely and send the request. The server still returns `wiener`'s account page — confirming the back-end does not check whether the authenticated session matches the requested `id` value.

**Step 3 — Access carlos's account**

Change the parameter to `id=carlos` and send:

```
GET /my-account?id=carlos
```

A `200` response returns Carlos's account page, including his API key. Copy the key and submit it to complete the lab.

### Conclusion

The application relied entirely on a user-supplied parameter to decide which account to display, with no server-side check that the session belonged to the requested user. This is a textbook example of **horizontal privilege escalation** — an attacker can access any other user's data simply by changing a parameter value.


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