I'd recommend not letting them do that. The CSS model used here is a good one to follow. there are CSS themes, but to become generally available any submissions would have to be audited. However, the user is free to insert a style sheet of their own for themselves (which btw, is just a crutch for old browsers; true CSS enabled browsers should support user-defined style sheets). UPDATE; Note of course this is exploitable as well, but requires the explicit action of the naive user, and there's not much you can do about that. If a user were to create a tainted sheet, make it publically available and convince others to use it (maybe it "looks cool")...
  • Did you come across this FAQ?
  • It is interesting to note that the acronym CSS is also used for Cross Site Scripting.
  • As for IMG, etc. you might find (~OT) WARNING: Live Ammo WAS: Re: Am I javascript or not? helpful, or frightening.

    • --
    perl -pew "s/\b;([mnst])/'$1/g"

    In reply to Re: Safe CSS Stylesheets by belg4mit
    in thread Safe CSS Stylesheets by osfameron

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