RE: Preventing cross site scripting

This post reminded me of another potential gotcha in HTML/JS filtering. All filtering activities should actually replace data with something, not just remove the data altogether.

Example, the following input string:

<BAD<BADTAG>TAG></BAD</BADTAG>TAG>

would result in the following if a remove system were in place:

<BADTAG></BADTAG>

Which could be harmful if rendered.
However, if the tag were to be replaced:

<BAD<X>TAG></BAD</X>TAG>

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We get a tad more html rendering safety.

this filtering stuff gets fun eh.

Regards,

Jer-

On Thu, 2003-06-19 at 19:16, Mutallip Ablimit wrote:
> Yes, replace all of the unacceptable tags with "", it will work fine.

-- 




Jeremiah Grossman
Chief Executive Officer
WhiteHat Security, Inc.
Tel: 408.492.1817

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