ComfyUI is a node-based diffusion model GUI, API, and backend. Prior to 0.28.0, GET /userdata/{file} served user-controlled HTML and SVG files with extension-de…

CVE-2026-56672 is a stored cross-site scripting (XSS) vulnerability in ComfyUI, a node-based diffusion model GUI and backend. Prior to version 0.28.0, the GET /userdata/{file} endpoint served user-uploaded HTML and SVG files with content types derived from file extensions, without forcing a download or sanitizing the MIME type. This allowed attackers to upload malicious .html or .svg files that, when visited by a victim, executed embedded scripts in the ComfyUI origin. Exploitation could lead to theft of browser-stored API tokens, settings, workflows, and the ability to make authenticated-equivalent API calls. The POST /userdata endpoint allowed arbitrary file content to be stored in the user's directory, enabling the attack vector. The /view endpoint had previously implemented MIME-type download forcing for dangerous files, but this protection was never applied to /userdata. The vulnerability has been patched in ComfyUI version 0.28.0 via a commit that enforces safe content-type handling for the userdata endpoint.