A Markdown file or a notebook output can carry a button that runs a JupyterLab command. Since 4.5.7 the first click on such a button opens a prompt naming the command, with Cancel, Run Once and Trust. Choosing Trust runs the command and marks the document trusted, so its later buttons run without a prompt. Which document gets marked is decided when the user answers, not when they click. Both …
JupyterLab 4.5.0 enabled copying and pasing cells through the system clipboard. The paste path parses clipboard text as cell JSON and inserts the cells without clearing metadata.trusted, so a payload can declare its own output as trusted. JupyterLab does not sanitize a trusted output and evaluates the <script> elements it contains, so pasting the cell runs attacker's JavaScript in the JupyterLab origin. The same payload with "trusted": false is sanitized. …
A language pack ships a Plural-Forms header saying how the language counts, for example nplurals=2; plural=(n != 1);. JupyterLab turns that string into a function with new Function, so the header gets executed. The check that meant to keep it safe was a regular expression. The regex was anchored at the start but not at the end, so it accepted any string that began with a valid plural rule and …
The vulnerability depends on user interaction by opening a malicious notebook with Markdown cells, or Markdown file using JupyterLab preview feature. A malicious user can access any data accessible from JupyterLite and perform arbitrary actions in JupyterLite environment.