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Date: Tue, 27 Aug 91 17:36:25 EST
From: Gene Spafford <spaf@CS.PURDUE.EDU>
Subject: File 9--Spaf's Response to Reviews of _Unix Security_
Just a couple of quick comments on some of the points made in the
reviews of "Practical Unix Security" in Volume #3.30.
Jim Thomas noted that we were brief in our explication of the laws
concerning computer intrusion. That was intended -- rather than giving
inexpert legal advice, we would prefer that the readers discover the
finer points through consultation with trained legal counsel. Although
we got advice from some experts in the area, we didn't feel up to a
formal treatment of the legal aspects related to security; we made
reference to other appropriate references in the appendix, and felt it
best left at that. Legal action is a serious step that should not be
undertaken solely on the basis of our treatment in the book!
Neil Rickert commented in his review about our recommendation not to
make the mail command the login shell on an account. He states that
the user would get the login shell using the shell escape (viz., doing
a ~ will result in a new invocation of mail), and this is not as clear
a problem.
On at least one system I have used, doing a "~!/bin/sh" has given me a
shell no matter what the login shell was. On some systems, escaping
into the editor with "~e" then allows the user to call up a shell. On
some versions (including SunOS), doing a "~:set SHELL=/bin/sh" lets me
bypass the current idea of login shell. Rather than give all the
what-ifs, we decided to recommend against the practice -- it is a major
accountability hole, too.
Neil caught an error with the statement about "su" -- we were both
thinking "suid" when we proofread it, and it slipped by. Mea culpa.
As for us making sound Unix scarier that it is, well, some versions of
Unix are pretty scary! We tried to keep the paranoia from overcoming
us, but after 500 pages of describing potential problems in all the
myriad forms of Unix, it became a losing battle. Then too, to get in
the proper frame of mind to do serious security work, one needs a touch
of paranoia.
That's probably one of the key concepts that we must not have stressed
enough later in the book -- not every system is vulnerable to every
problem we described. Some systems have been tightened up, and others
are like Swiss cheese.
Simson and I are grateful for any other comments people care to make,
here or in mail.
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End of Computer Underground Digest #3.33
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