Potential Information Leakage via Mermaid Diagram

Summary

Cursor supports a tool called Mermaid to render diagrams. While testing it was observed that mermaid allows embedding images which then get rendered by Cursor in the chat box.

An attacker can use this to exfiltrate sensitive information to a third-party attacker controlled server through an image fetch after successfully performing a prompt injection. A malicious model (or hallucination/backdoor) might also trigger this exploit at will.

Some additional bypasses not covered in the [initial fix to this issue](https://github.com/cursor/cursor/security/advisories/GHSA-43wj-mwcc-x93p) were discovered and reported in this advisory.

Impact

This issue requires prompt injection from malicious data (web, image upload, source code) in order to exploit. In that case, it can send sensitive information to an attacker-controlled external server.

Remediation

All remote images are removed from the mermaid diagram before rendering.