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Re: procmail
From: casper () HOLLAND SUN COM (Casper Dik)
Date: Tue, 22 Jul 1997 09:11:11 +0200


On Mon, 21 Jul 1997 16:50:56 +0200, Casper Dik wrote:
Shells will not honor meta characters inside variables.

The shell will first parse (the phase in which meta chacretsr and keywords
are detected) and only then will it do variabel substitution.

Then it'll split stuff in words and only then wildcard expansion is done.

There's some weird effect with tcsh (I don't know if that's standard csh
behavior). When your shell script does a `set foo=$1' and the first
argument is "xx PATH=~ftp/incoming:/usr/bin:/bin" it will do two
simultaenous variable assignments, and thus overwrite the PATH variable
with the string the attacker specified.

Not sure if that qualifies as metacharacter expansion, but it's definitely
scary:-) Metamail had this problem, fwiw.


Most likely because Csh/Tcsh variabel assignments are treated different
from sh assignment (which are part of the syntax; in csh/tcsh they're
part of the command language)

in Csh/tcsh you must quote the assignment.

The worst thing csh/tcsh do, however, is an "eval" on the variable that
are imported to local variables (HOME->hoem, TERM-> term PATH->path, etc)

So any set-uid/set-gid C-shell script or a C-shell script "captive" login;
they're all easily broken.

This is fixed in later tcsh revisions.

There are simply too many weird things in tcsh/csh to use them as a scripting
language for scritps otehr than .login/.cshrc etc.

Casper



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