Discourse vulnerable to stored-dom XSS via Facebook Oneboxes

Discourse is an open-source discussion platform. Prior to version 3.2.3 on the stable branch and version 3.3.0.beta3 on the tests-passed branch, an attacker can execute arbitrary JavaScript on users’ browsers by posting a specific URL containing maliciously crafted meta tags. This issue only affects sites with Content Security Polic (CSP) disabled. The problem has been patched in version 3.2.3 on the stable branch and version 3.3.0.beta3 on the tests-passed branch. As a workaround, ensure CSP is enabled on the forum.