Discourse is an open-source discussion platform. Prior to version 3.0.1 of the "stable" branch and version 3.1.0.beta2 of the "beta" and "tests-passed" branches, a maliciously crafted URL can be included in a user's full name field to to carry out cross-site scripting attacks on sites with a disabled or overly permissive CSP (Content Security Policy). Discourse's default CSP prevents this vulnerability. The vulnerability is patched in version 3.0.1 of the "stable" branch and version 3.1.0.beta2 of the "beta" and "tests-passed" branches. As a workaround, enable and/or restore your site's CSP to the default one provided with Discourse.