Cursor is a code editor built for programming with AI. In versions below 1.3, Mermaid (which is used to render diagrams) 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. 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. This is fixed in version 1.3.
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.