Clipboard based cross-site scripting (blocked with default CSP) in Kanboard

Kanboard is project management software that focuses on the Kanban methodology. Due to improper handling of elements under the `contentEditable` element, maliciously crafted clipboard content can inject arbitrary HTML tags into the DOM. A low-privileged attacker with permission to attach a document on a vulnerable Kanboard instance can trick the victim into pasting malicious screenshot data and achieve cross-site scripting if CSP is improperly configured. This issue has been patched in version 1.2.29.