The usual way to handle something like this, particularly if you don't know what will cause harm, is to select a set of tags and attributes that should be allowed and remove everything else.

For an example: see perlmonks. Below the input box is the list of tags that will work. The reason they do this is simple: who knows what might cause harm? But we can be reasonably certain the strong and emphasis tags are ok.

-Paul

In reply to Re: Removing malicious HTML entities (now with more questions!) by jettero
in thread Removing malicious HTML entities (now with more questions!) by Lawliet

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
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  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
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    [ &#91;
    ] &#93;
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  • See Writeup Formatting Tips and other pages linked from there for more info.