In MISP before 2.4.193, menu_custom_right_link_html parameters can be set via the UI (i.e., without using the CLI) and thus attackers with admin privileges can conduct XSS attacks against every page.
https://github.com/MISP/MISP/releases/tag/v2.4.193
https://github.com/MISP/MISP/commit/09a43870e733f79ffa33753ddc7bce3cbb5a5647