Anonymous cache poisoning via XHR requests in Discourse

Discourse is an open source platform for community discussion. In affected versions an attacker can make craft an XHR request to poison the anonymous cache (for example, the cache may have a response with missing preloaded data). This issue only affects anonymous visitors of the site. This problem has been patched in the latest version of Discourse. Users are advised to upgrade. Users unable to upgrade should disable anonymous cache by setting the `DISCOURSE_DISABLE_ANON_CACHE` environment variable to a non-empty value.