This link describes an exploit into my app using fckEditor: http://knitinr.blogspot.com/2008/07/script-exploit-via-fckeditor.html
How do I make my app secure while still using fckEditor? Is it an fckEditor configuration? Is it some processing I'm supposed to do server-side after I grab the text from fckEditor?
It's a puzzle because fckEditor USES html tags for its formatting, so I can't just HTML encode when I display back the text.
Sanitize html server-side, no other choice. For PHP it would be HTML Purifier, for .NET I don't know. It's tricky to sanitize HTML - it's not sufficient to strip script tags, you also have to watch out for on* event handlers and even more, thanks to stupidities of IE for example.
Also with custom html and css it's easy to hijack look and layout of your site - using overlay (absolutely positioned) which covers all screen etc. Be prepared for that.