draw.io is a configurable diagramming and whiteboarding application. Prior to 31.1.5, the GraphML decoder contains a prototype-pollution vulnerability. Attacker-controlled GraphML reference keys can address inherited object properties, including prototype objects, and the decoder can then assign attacker-controlled attributes to those objects. Importing a malicious GraphML file can trigger client-side prototype pollution. In the advisory-supported cross-site scripting chain, the editor is opened in Trello mode and the user invokes the Trello integration after the import, allowing the polluted state to execute script in the draw.io origin; an existing Trello connection is not required. This vulnerability is fixed in 31.1.5.