All systems are operational.
Booru is down for maintenance until some security patches (unrelated to the PHP2Shell that was recently announced) can be applied.
Update: Updated the server and codebase as well, sorry for the long downtime.
Forums, blogs, the wikis have been taken down temporarily, waiting on a security patch to be released before they are restored.
Update: Postponing the reopening until Thursday 22nd (~ 16:00 UTC-0), there might be still be a related vulnerability.