Race conditions, transactions and free parking (39c3)

ORM's and/or developers don't understand databases, transactions, or concurrency. After the [Air France-KLM dataleak](https://media.ccc.de/v/37c3-lightningtalks-58027-air-france-klm-6-char-short-code) I kept repeating this was not a real hack, and confessed I always wanted to hack a system based on triggering race conditions because the lack of proper transactions. This was way easier than expected. In this talk I will show how just adding `$ seq 0 9 | xargs -I@ -P10 ..` can break some systems, and how to write safe database transactions that prevent abuse. In this talk I will explain what race conditions are. Many examples of how and why code will fail. How to properly create a database transaction. The result of abusing this in real life (e.g. free parking). Licensed to the public under http://creativecommons.org/licenses/by/4.0 about this event: https://events.ccc.de/congress/2025/hub/event/detail/race-conditions-transactions-and-free-parking