Aucbvax.2953
fa.unix-wizards
utzoo!decvax!ucbvax!unix-wizards
Sat Sep  5 06:25:57 1981
Re: /usr/spool/mail
>From MathStat.jmrubin@Berkeley Sat Sep  5 06:15:14 1981
	From csvax:unix-wizards Sat Sep  5 05:33:33 1981
	Subject:  Re: /usr/spool/mail
	Newsgroups: fa.unix-wizards
	>From James.Gosling@CMU-10A Sat Sep  5 05:23:07 1981
	If /usr/spool/mail is writable it's really easy to become super-user.
	
	1. copy the shell to the file /usr/spool/mail/root
	2. make it suid
	3. send mail to root
	
	When the mail is sent to root the delivery program only appends the mail to
	the mailbox and chowns the file to root.  *poof* you have a suid root shell.
	The easiest way to stop this is to not have /usr/spool/mail be writable.
	
						James.
	
	
	I don't think this would work because writing on a setuid file
usually shuts off the setuid bits (and setgid bits); of course, this is
installation dependent.  Of course, chown is a priviledged call, but
I suspect chown also turns off the setuid bits.  (If it doesn't, then
it should!)
					Joel Rubin

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