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From bugzi...@apache.org
Subject [Bug 54764] XSSF : Vulnerable to entity expansion attack
Date Mon, 04 Aug 2014 19:25:34 GMT
https://issues.apache.org/bugzilla/show_bug.cgi?id=54764

--- Comment #4 from Nick Burch <apache@gagravarr.org> ---
As of r1615720, there are no issues with loading files at the OPC level with
hand-crafted nested entities, on the default JVM xml parser. The affected part
will be skipped, so if it was eg docProps/core.xml then you just won't see any
core properties, but if it was ContentTypes then the whole OPCPackage will be
rejected as invalid.

XMLBeans is still an issue though. With XMLBeans 2.3 (the default we ship),
it'll hang. With XMLBeans 2.6, the built-in entity expansion detection will
trigger at 10,240 bytes expanded and halt parsing. The problem is that XMLBeans
doesn't reset the state of the SaxHandler it uses, and that seems to be some
sort of singleton. That means that once one naughty file has blown up, all
subsequent files will fail to parse as it still thinks it's in the same
too-large entity even though it isn't!

It would seem that we need to either fix or workaround this xmlbeans 2.6 bug,
then upgrade the xmlbeans runtime that we ship + recommend.

(Because XMLBeans runtimes are happy with older generated classes, but not
newer ones, and because some of our users are on platforms which ship + depend
on older XMLBeans instances like 2.3, we shouldn't just upgrade the version of
xmlbeans we use to compile the schemas with. Instead, once the problem is
fixed, we should look to ship 2.3 for compiling but 2.6/fixed by default for
running)

If someone has some time to work on this, the thing to do would be to bump the
xmlbeans runtime in your dev env up to 2.6, attach the xmlbeans sources, enable
the commented out part of TestXSSFBugs.bug54764, then try to work out where the
caching of the SaxHandler happens. From that, it'll hopefully be possible to
find out if we can workout the lack of byte expansion count reset or not

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