How We Took Over ChatGPT Accounts
The point
Parameter Labs chained flaws in ChatGPT HTML previews to take over accounts. Code in a sandboxed iframe triggered the MathLive keyboard via postMessage, which used innerHTML to inject HTML into the parent page. That allowed JavaScript execution despite CSP rules, using the YouTube oEmbed endpoint.
Why it matters
Builders must audit postMessage handlers and CSP allowlists, not just iframe sandboxes.
Key details
- A shared link could exfiltrate private data or act for a signed in visitor
- OpenAI closed the hole
- OpenAI paid a $5,000 bug bounty
Original ~3 min → 25 sec here Source: Simon Willison, Oct 31, 2026