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Date: Sun, 31 Jul 2016 12:24:48 -0500
From: "Joshua J. Drake" <oss-security-dbduaf@...p.org>
To: oss-security@...ts.openwall.com
Cc: lazytyped <lazytyped@...il.com>
Subject: Re: Re: Use after free in my_login() function of
 DBD::mysql (Perl module)

Certainly buffer overread and related errors can sometimes be security
vulnerabilities. The biggest question that differentiates those cases from
non-security bugs (aka "lame bugs") is whether or not the the out-of-bounds
data can actually be accessed by an attacker (directly or otherwise).If the
data is read (and thus would cause an ASAN failure) then it's conceivable that
nothing is actually done with the out of bound data at all... Writes are
generally easier to make assumptions about.

In the future, Maybe it would help to partner with someone more experienced to
determine severity before public disclosure. Also, asking the list for its
collective advice might also prove fruitful (instead of asking for a CVE
straight away).

Don't be afraid to be more explicit. If you don't know -- just say "I don't
know if attackers can get anything out of this, but similar bugs like" .. <real quote>"use
after free's can be serious and potentially lead to malfunction and security
issues."</real quote> "Do you see any potential for abuse by attackers?"A

Also, realize that this type of inquiry will help both you and the developer
learn about security bugs and in general will lead to improved awareness to all
parties that happen across your communications.

Again, just my $0.02 when I read this thread.

Joshua

On Sat, Jul 30, 2016 at 10:27:09AM -0400, Hanno Böck wrote:
> On Fri, 29 Jul 2016 20:42:03 -0700
> lazytyped <lazytyped@...il.com> wrote:
> 
> > Well, AddressSanitizer should have told you whether the access is a
> > read access (as I suspect) or a write access. A bit of code
> > inspection (or follow up from the code maintainer) should add to the
> > picture.
> 
> It's my (maybe poor / limited) understanding that most use after free
> bugs are actually reads, but still can lead to code execution, e.g. if
> the read includes function pointers. This is probably not the case in
> this example (but I previously had an example where I thought it's not
> exploitable for similar reasons, and later got told by people who
> understand this stuff much better that they disagree).
> 
> > It would be great if we could get a bit more triaging by the owner of
> > the code or the submitter before declaring the bug one thing or the
> > other (especially in these days of projects like yours that bring in
> > a lot of reports -- and don't get me wrong, this is a very valuable
> > effort).
> 
> I understand your wish here, but I am afraid it doesn't match up well
> with the reality we are in.
> 
> I had similar discussions before, but I think there is a very obvious
> problem here: The tools we use to find these bugs (asan+afl) are dead
> simple and there are a lot of people out there using them, finding and
> reporting bugs. The number of people with a detailed knowledge of
> memory corruption on the other hand is small.
> 
> Generally this is a good thing, as it means more people finding bugs.
> But we have a large number of people who can use the tools to find
> these bug classes, but who aren't neccessarily able to judge the
> severity. And that definitely includes me (although I learned a lot in
> the past year, but I've been accused both in over and underplaying bugs
> in the past).
> My approach to this is that I simply try to choose my wording that it
> matches what I know and if I can't say anything reasonable about
> exploitability I simply don't.
> 
> As for CVEs, it's my impression that MITRE right now has a policy that
> they give one for almost any memory safety issue and that they don't
> require an explicit exploit scenario. E.g. my impression is that buffer
> overreads, as long as they aren't simply in a command line tool, almost
> always get CVEs.

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