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

Vulnerability Description

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.

References

• https://github.com/kanboard/kanboard/security/advisories/GHSA-hjmw-gm82-r4gv
• https://github.com/kanboard/kanboard/commit/26b6eebb78d4306e48b836a58f7c386251aa2bc7
• https://github.com/kanboard/kanboard/commit/c9c187206700030c43493b80fd599b4d096cb713