Poorly written XML parsers (and I've written my fair share) are always open to DOS attacks; XML has no upper bound on element names, attribute value length, stack depth ...

http://en.wikipedia.org/wiki/Billion_laughs

Same is mostly true of JSON parsers as well of course.

If you let potentially hostile users feed arbitrary data into any of these, even a totally non-buggy, perfectly conformant parser is wide-open to being abused via DOS.

That's a nasty little xml document. Interesting how any kind of simple macro expansion system is wide open to this kind of attack.

My guess is that to distinguish between 'legitimate' cases and 'attacks' is on par with solving the halting problem.

Somehow I'm surprised that XML/JSON libraries written since the 90s would have the same core flaw as string libraries written in the 70s.

I know I shouldn't be. But here I am, surprised.

Well, they're both written in the same language. That ought to be a Big Fat Steaming Clue (TM).

Someday, I'd like to see a nice library written in something like O'Caml or Haskell exposed as a C interface that exists solely to be a library. I know it's technically possible today, but it doesn't seem to have penetrated into the public consciousness that even a C library doesn't actually have to be written in C anymore. (It may not be slick yet, but only because people aren't doing it, chicken and egg. There's no fundamental stopper.) I sure as hell wouldn't write a "C" library in C if I had anything remotely resembling a choice.

(Of course, that only solves string bobbles, not the "infinite memory consumption required" problem, but even then those other languages can have somewhat cleaner, clever solutions than in C.)

The face that no such libraries exist might be interpreted as a Big Fat Steaming Clue (trademark used without license).

Language geeks need to start thinking seriously about practical infrastructure issues before any of this happens. The existing infrastructure people aren't going to start using Haskell simply because you tell them too.

Here's the original press release from the company:

http://www.codenomicon.com/news/press-releases/2009-08-05.sh...

And a CERT-FI advisory:

http://www.cert.fi/en/reports/2009/vulnerability2009085.html

Also the expat-bug and expat-discuss mailing lists were very active in January/February with seemly related issues:

http://mail.libexpat.org/pipermail/expat-bugs/2009-January/t...

http://mail.libexpat.org/pipermail/expat-discuss/2009-Februa...

The original article sounds like a scare/marketing piece:

    "Targets: Anything that uses XML"

Pretty much a useless article without some explanation of what the flaw is.

Agreed. Also: "3-dimensional programs" are affected!

So then there is nothing wrong with XML… There is everything wrong with a few parsers.

Wouldn't a better title be "XML Parser Flaws Doom Computing World"?

Because of the nature of the flaw, details have not been published. (Also see the original article at http://www.codenomicon.com/labs/xml/) Not clear what can be done about the issue, and how bad the issue is. Should we just wait for it to be resolved?

Pretty skeptical this flaw could be in "virtually every open-source XML library available". Seems unlikely a million brains collectively missed whatever this is.

You are underestimating how easy it is to write insecure C code.

But it would be nice to know if this is expat, libxml2, or what.

My understanding is it's not a single flaw. Virtually every XML library available is flawed, but each in their own way.

"xml parser flaws"

Unless they can trigger an infinite loop I'm not really worried about Java/Python based web services being affected. Any exception should be caught on a per-request basis.