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re: XMLP WG Response on "SOAP and the Internal Subset"

From: Rich Salz <rsalz@datapower.com>
Date: Tue, 10 Dec 2002 21:32:10 -0500 (EST)
To: Larry Masinter <LMM@acm.org>
cc: "www-tag@w3.org" <www-tag@w3.org>, "ietf-xml-use@imc.org" <ietf-xml-use@imc.org>
Message-ID: <Pine.LNX.4.44L0.0212102121030.28307-100000@smtp.datapower.com>

I haven't digest all your note yet, but this did immediately come to mind:

> It would be useful to define XMLP in terms of the 'canonical InfoSet':
> the Infoset of the RFC 3076 Canonical XML of the document. In
> particular, all entities are expanded and DTDs removed from the
> Canonical XML.

Are you really advocating a third definition of XML, putting the
XPath1.0 model on a par with XML1.0 and the XML Infoset?

> > Security is another concern.  Although we have not formally
> > demonstrated that XML with internal subset is less secure, several
> > members of the workgroup shared an intuition that entity
> > substitution, attribute defaulting, and other manipulation of the
> > message content was more likely to lead to security exposures,
> > denial of service attacks (e.g. the billion laughs entity attack),
> > etc.
> Any message from any unauthenticated source introduces the potential
> for a denial of service attack, merely from the possibilities of
> overly long URI paths, element names, attribute values, content,
> etc. When parsing any message from an unauthenticated source, it's
> necesasry to insure that parsing the message doesn't consume undue
> resources in the receiver.  The parsing and substitution of entity
> definitions is just one of many such considerations. ...

DoS is only one issue; the other -- and in my view, the more important
one -- is that my server doesn't chase down external URL's just because
someone defined an entity in a DTD.  Was that not clear from
the original note?

> things more complicated. What is the complexity cost of receivers
> ignoring processing instructions vs. explicitly checking for them and
> disallowing them?

Well, by saying "don't send them", then a message that includes PI's
is out of spec, and the receiver can do whatever it wants, including
acting on them.  Mandating "ignore them" seems like more work, to me.
Received on Tuesday, 10 December 2002 21:32:11 UTC

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