AnythingLLM is an application that turns pieces of content into context that any LLM can use as references during chatting. Prior to version 1.12.1, AnythingLLM's in-chat markdown renderer has an unsafe custom rule for images that interpolates the markdown image's alt text into an HTML alt="..." attribute without any HTML encoding. Every call-site in the app wraps renderMarkdown(...) with DOMPurify.sanitize(...) as defense-in-depth, except the Chartable component, which renders chart captions with no sanitization.

The chart caption is the natural-language text the LLM emits around a create-chart tool call, so any attacker who can influence the LLM's output, most cheaply via indirect prompt injection in a shared workspace document, or directly if they can create a chart record in a multi-user workspace, can trigger stored DOM-level XSS in every other user's browser when they open that conversation. AnythingLLM chat history is loaded server-side via GET /api/workspace/:slug/chats and rendered directly into the chat UI. Version 1.12.1 contains a patch for this issue.