marimo before 0.23.9 contains a reflected cross-site scripting vulnerability in the notebook page that allows unauthenticated attackers to inject arbitrary JavaScript by exploiting improper escaping of single quotes in the file query parameter reflected into an inline JavaScript string literal. Attackers can craft a malicious link with a payload beginning with new to bypass the 404 check and inject JavaScript into the page, which executes without Content-Security-Policy restrictions in the origin of a victim's marimo server.

The marimo bot workflow uses one-second timestamps to reject pull request changes made after a maintainer authorizes a test release. An external contributor can exploit a same-second race to execute code and publish attacker-controlled packages to TestPyPI and npm.