How it was found

I know this may not qualify for a bounty since it's a DoS, but I believe you'd rather get sensitive reports through HackerOne rather than Maniphest. (PS: mongoose.)

Steps to reproduce

• In Dashboards, create a new Text Panel (let's say it would get the object reference W1 on creation).
• In the Create New Panel dialog, embed the panel view onto itself with Remarkup: {W1}
• Phabricator should now bravely attempt to render this, and choke.

Impact

Significantly disruptive in an install where any user may create a dashboard (I think that's true by default), since they would then be able to embed this eldritch panel in, say, a Maniphest comment, forever ruining rendering for all of task, feed, and likely homepage, views.