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    SubjectRe: Unexecutable stack
    On Mon, 27 Dec 1999, Steve VanDevender wrote:

    > Richard B. Johnson writes:
    > > The notion of a secure stack implies that you get some kind of security
    > > by making the stack non-executable. This theory has, to the best on
    > > my knowledge, never been shown to have merit, much less proof. The
    > > old games of loading executable opcodes into local data on the stack,
    > > overwriting the return address with that data (to point to the code
    > > you want to execute), then causing an exception (stack overrun) to
    > > make it happen, are not something you could encounter with the current
    > > network daemons.
    > >
    > > You would need a local account, with root access, to even experiment.
    > I run a couple of large Solaris 7 systems with the
    > "noexec_user_stack" option enabled. This defeats nearly all root
    > exploits based on stack overflows; I've tried them and intruders
    > have tried them without success. Making the stack non-executable
    > really does help.

    So how many root exploits have you actually had? And, how many
    attempts? I have, at last count, 54 Suns, 126 Alphas, a few hundred
    ix86/Linux, plus slightly less than 1,000 Win/Win-NT machines on
    this very site where we have 1,200 engineering employees. Most
    all the Suns, Alphas, and Linux machines are not filtered by
    a firewall.

    We have never had a known, provable break-in of any kind, not
    counting the engineers blue-screening the Windows machines
    by throwing funny packets at them.

    > You don't quite seem to understand the mechanism of stack buffer
    > overflow exploits. The buffer overflow does not cause an

    I understand it exactly and precisely. It is likely that I was
    the first to demonstrate this in the late '70s.

    Dick Johnson

    Penguin : Linux version 2.3.13 on an i686 machine (400.59 BogoMips).
    Warning : The end of the world as we know it requires a new calendar.
    Seconds : 363688 (until Y2K)

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