The LinkedCustomFields plugin for MantisBT allows users to link values between two custom fields, creating linked drop-downs. Prior to version 2.0.1, cross-site scripting in the MantisBT LinkedCustomFields plugin allows Javascript execution, when a crafted Custom Field is linked via the plugin and displayed when reporting a new Issue or editing an existing one. This issue is fixed in version 2.0.1. As a workaround, one may utilize MantisBT's default Content Security Policy, which blocks script execution.
https://github.com/mantisbt-plugins/LinkedCustomFields/security/advisories/GHSA-2f37-9xpx-5hhw
https://github.com/mantisbt-plugins/LinkedCustomFields/pull/11
https://github.com/mantisbt-plugins/LinkedCustomFields/issues/10