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Re: Troff dangerous.
From: robert () CYRUS WATSON ORG (Robert Watson)
Date: Tue, 27 Jul 1999 04:59:30 -0400


On Sun, 25 Jul 1999, Pete wrote:

But as for your statement I would prefer a setuid/gid man (to a dedicated
uid and gid) thus *when* your troff is compromised. It will not have the
authority to compromise your system.

I agreed entirely with your rant until this point.

Making your man programs setuid man does not improve security, only
performance due to the caching effect.

Let me give an example: because man is setuid to the man uid, the binary
must be owned by uid man.  As a result, unless the file system is
read-only or the immutable bit is used on supporting operating systems, it
is writable by the man uid.  When you have a trojan man page, the trojaned
code runs as uid man, and as such may now modify the man program, etc.  If
root runs man, it will run the modified man program, and if the man uid is
careful to remove the setuid bit from the executable (something it may do
as it owns the file) then this new code now runs as root the next time a
trojaned man page is executed.

All setuid man does is allow a shared cache on man pages, it does not
isolate security problems assocated with the man system--any user who runs
the man command gives up control of their credentials to any user who can
modify the man binary, or trojan a man page.

  Robert N M Watson

robert () fledge watson org              http://www.watson.org/~robert/
PGP key fingerprint: AF B5 5F FF A6 4A 79 37  ED 5F 55 E9 58 04 6A B1
TIS Labs at Network Associates, Computing Laboratory at Cambridge University
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