Decidim is a participatory democracy framework. Starting in version 0.10.0 and prior to versions 0.26.9, 0.27.5, and 0.28.0, a race condition in the endorsement of resources (for instance, a proposal) allows a user to make more than once endorsement. To exploit this vulnerability, the request to set an endorsement must be sent several times in parallel. Versions 0.26.9, 0.27.5, and 0.28.0 contain a patch for this issue. As a workaround, disable the Endorsement feature in the components.