CVE-2026-25640: Pydantic AI has Stored XSS via Path Traversal in Web UI CDN URL

A Path Traversal vulnerability in the Pydantic AI web UI allows an attacker to serve arbitrary JavaScript in the context of the application by crafting a malicious URL. If a victim clicks the link or visits it via an iframe, attacker-controlled code executes in their browser, enabling theft of chat history and other client-side data.

This vulnerability only affects applications that use:

• Agent.to_web to serve a chat interface
• clai web to serve a chat interface from the CLI

These are typically run locally (on localhost), but may also be deployed on a remote server.