NamelessMC is a free, easy to use & powerful website software for Minecraft servers. In version 2.1.4 and prior, the forum allows users to post iframe elements inside forum topics/comments/feed with no restriction on the iframe's width and height attributes. This allows an authenticated attacker to perform a UI-based denial of service (DoS) by injecting oversized iframes that block the forum UI and disrupt normal user interactions. This issue has been patched in version 2.2.0.
https://github.com/NamelessMC/Nameless/security/advisories/GHSA-2prx-rgr7-hq5f
https://github.com/NamelessMC/Nameless/releases/tag/v2.2.0
https://github.com/NamelessMC/Nameless/commit/caa42a975338a13fbc1658e8c440108f16135643