Mysterious security hole

[Michael Ewan]

In article <91161.131540SCHDAVZ at YaleVM.YCC.Yale.Edu>, SCHDAVZ at YaleVM.YCC.Yale.Edu (Dave Schweisguth) writes:
|>  
|> The 'login' command initializes PATH with (among other useful directories)
|> '.'. 'su' leaves '.' out. A footnote to a Unix book I have here hints at a
|> security hole involving the _position_ of '.' in PATH, claiming that having
|> '.' first is dangerous. It doesn't say why.
|>      These add up to something screwy with '.'. Can someone explain why root/
|> Joe User ought/ought not have '.' in his/her path, and if so should it be
|> first, last, or anywhere, and (this is the good part) why? The system is an
|> SGI Personal Iris, IRIX v3.3.2, if it matters.

Having . in your path (especially root's) is dangerous because someone could put
a trojan horse program in / (or your home dir) that would execute instead of the
system command of the same name.  For example:  someone could put a command in / and
call it 'ls', that was acctually a shell script that did rm -fr /' you'd have a real
problem.  So if you have . in your path you put it last so destructive shell
scripts can't masquerade as system commands.  That is you'll get /bin/ls instead
of ./ls.

Mike

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