--On Wednesday, November 05, 2003 8:27 PM -0500 "Steven M. Christey"
<coley (at) mitre (dot) org [email concealed]> wrote:
>
> Maybe I'm alone in this, but I find web browser bugs like these to be
> among the most complex and difficult-to-understand vulnerabilities
> that get reported. An aspect of that complexity often seems to
> involve crossing several intended security "boundaries" in the
> process, taking advantage of design choices that, by themselves, don't
> seem to be that security-relevant. Example: one might think that
> non-random locations for software components would be a good thing,
> but it's a factor in a number of web client bugs. (Another aspect of
> that complexity comes from advisories that simply include exploit code
> using obscure components or elements but don't suggest where the issue
> actually lies, but that's a different matter.)
>
But isn't this crossing of security boundaries essentially caused by the
same mental error that buffer overflows are caused by? Trusting
untrustable input is at the foundation of each, isn't it?
If you create a boundary that says, "This is private space. Only trusted
data can enter.", yet you decide that, for whatever supposedly legitimate
reason you want to allow input from some other space, isn't it incumbent
upon you as the programmer to disallow all but "proper" input?
It appears to me that this chaining of weaknesses is nothing more than an
extension of the same problem that each weakness has individually, i.e. the
failure of the programmer to do "bounds" checking. Granted, it's more
complex to figure out how to exploit the weaknesses, but the reason the
exploit is possible is because of the same naive trust that fails us every
time.
We need a paradigm shift in programming from "allow all but the known bad"
to "disallow all but the known good", don't we?
Paul Schmehl (pauls (at) utdallas (dot) edu [email concealed])
Adjunct Information Security Officer
The University of Texas at Dallas
AVIEN Founding Member
http://www.utdallas.edu
<coley (at) mitre (dot) org [email concealed]> wrote:
>
> Maybe I'm alone in this, but I find web browser bugs like these to be
> among the most complex and difficult-to-understand vulnerabilities
> that get reported. An aspect of that complexity often seems to
> involve crossing several intended security "boundaries" in the
> process, taking advantage of design choices that, by themselves, don't
> seem to be that security-relevant. Example: one might think that
> non-random locations for software components would be a good thing,
> but it's a factor in a number of web client bugs. (Another aspect of
> that complexity comes from advisories that simply include exploit code
> using obscure components or elements but don't suggest where the issue
> actually lies, but that's a different matter.)
>
But isn't this crossing of security boundaries essentially caused by the
same mental error that buffer overflows are caused by? Trusting
untrustable input is at the foundation of each, isn't it?
If you create a boundary that says, "This is private space. Only trusted
data can enter.", yet you decide that, for whatever supposedly legitimate
reason you want to allow input from some other space, isn't it incumbent
upon you as the programmer to disallow all but "proper" input?
It appears to me that this chaining of weaknesses is nothing more than an
extension of the same problem that each weakness has individually, i.e. the
failure of the programmer to do "bounds" checking. Granted, it's more
complex to figure out how to exploit the weaknesses, but the reason the
exploit is possible is because of the same naive trust that fails us every
time.
We need a paradigm shift in programming from "allow all but the known bad"
to "disallow all but the known good", don't we?
Paul Schmehl (pauls (at) utdallas (dot) edu [email concealed])
Adjunct Information Security Officer
The University of Texas at Dallas
AVIEN Founding Member
http://www.utdallas.edu
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