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Date: Tue, 10 Feb 2015 12:57:05 -0500
From: Rich Felker <>
Subject: Re: wordexp(3)

On Tue, Feb 10, 2015 at 08:27:56PM +0300, Solar Designer wrote:
> Hi,
> I found this curious and relevant to this list, off Twitter:
> (x250) <%worr> RT @FioraAeterna: oh my gosh, Apple's libc literally implements "wordexp" by shelling out to perl:
> <worr> So yesterday, @FioraAeterna tweeted this: I've decided to take a tour of wordexp(3) implementations
> <@worr> They can't all be that bad
> (x2) <@worr> NetBSD and FreeBSD both use a sh builtin to implement wordexp(3):
> (x5) <@worr> OpenBSD wins the wordexp(3) contest, by refusing to implement it altogether.
> <@worr> Correction: glibc implements a huge recursive descent parser, and only shells out when it needs to do subshell expansions.
> <@worr> tbh, wordexp(3) is an antifeature. Maybe even a misfeature.
> <@worr> Here's the implementation, btw:;a=blob;f=posix/wordexp.c;h=26f3a2653feba2b1a5904937d9d6b58c32109e24;hb=a39208bd7fb76c1b01c127b4c61f9bfd915bfe7c#l872
> <@worr> Continuing on my tour of wordexp(3) implementations, here's Illumos': It constructs a small shell script and runs it

POSIX is explict that the wordexp interface is designed such that
invoking a shell is one valid implementation choice. My view on all
this is that pretty much anything wordexp-related is not CVE-worthy;
wordexp simply is not a proper tool to be using in programs dealing
with untrusted inputs -- either untrusted input strings, or untrusted
environment contents. Obviously implementations using /bin/sh were
vulnerable to shellshock on systems where /bin/sh is bash.


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