Re: [Caml-list] Re: [oss-security] CVE request: Hash DoS vulnerability (ocert-2011-003)

["Gerd Stolpmann" <info@gerd-stolpmann.de>]

> On Tue, Feb 07, 2012 at 08:34:12AM +0000, Richard W.M. Jones wrote:
>> On Mon, Feb 06, 2012 at 06:10:15PM -0700, Kurt Seifried wrote:
>> > On 02/06/2012 06:05 PM, Kurt Seifried wrote:
>> > > So going through various things looks like Ocaml is vulnerable and
>> has
>> > > not had a CVE # assigned for this issue yet.
>> > >
>> > > Discussion of the issue takes place on the mailing list, here is a
>> link
>> > > for the originating thread:
>> > >
>> > >cc
>> > >
>> > > There doesn't appear to be a fix yet.
>> > >
>> > >
>> >
>> > Please use CVE-2012-0839 for this issue.
>>
>> Red Hat BZ:
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=787888
>>
>> Rather than changing every app that uses Hashtbl, I'd prefer to fix
>> this upstream by choosing a random seed for hash tables unless the
>> caller explicitly sets one or sets an environment variable to disable
>> this.
>>
>> In Perl, the seed is a random number chosen when the Perl interpreter
>> starts up.  This is low overhead, but still leaves a (much more
>> theoretical) attack where someone can determine the seed from a
>> long-running process using some other method and still attack the hash
>> table.
>>
>> In Python there is an environment variable you can set to disable
>> randomized hash tables.  Further Python discussion here:
>> http://bugs.python.org/issue13703
>> http://mail.python.org/pipermail/python-dev/2012-January/thread.html#115465
>
> No comment at all?  This is an exploitable CVE ...

Well, we discussed it already (
http://groups.google.com/group/fa.caml/browse_frm/thread/83d76b4869606c86/3c7eb9abe7d6aa50?tvc=1&q=hashtbl#3c7eb9abe7d6aa50
), and there was no consensus that the "Perl way" is the preferrable one.
OCaml 3.13 will provide options for Hashtbl allowing it pass a seed, but
only in a case by case way. What will not be included in OCaml 3.13 is
access to RNGs with entropy injection (i.e. it is left to the programmer
to solve this difficulty).

IMHO, the situation with 3.13 is not yet satisfying from a security
standpoint, because Ocaml does not guide the developer to a safe solution.

Currently, the only way for library developers to fix their product for
3.12 is to restrict the size of the hashtables coming from untrusted
sources. For example, Ocamlnet-3.5.1 contains a fix for the HTTP and CGI
protocol interpreters in this style. I don't know if there are fixes in
other libraries.

Gerd

>
> Rich.
>
> --
> Richard Jones
> Red Hat
>
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