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Date: Tue, 30 Sep 2014 17:35:21 +0000
From: Zach Wikholm <>
To: "" <>
Subject: Re: Healing the bash fork

Hey everybody,

I don't think I've ever actually written to the list, but we also haven't ever encountered a bug like this. 

Personally, I think a bullet point list (or whatever people use these days) is needed of what all is actually wrong, what is broken and how we as a community can assist is desperately needed. Last time I checked there are a total of 6 CVEs currently assigned to bash related vulnerabilities and I'm sure there are more to come.  

 If there is one already, I apologize in advance. 

Zach W.
From: Ed Prevost <>
Sent: Tuesday, September 30, 2014 8:31 AM
Subject: Re: [oss-security] Healing the bash fork

On 9/30/2014 8:08 AM, Tavis Ormandy wrote:
> On Tue, Sep 30, 2014 at 8:02 AM, Mark R Bannister
> <> wrote:
>>>> Florian's prefix/suffix patch is not going to protect against the setuid/setgid exploit that I reported to this list last week.> >
>>>> I discuss the setuid/setgid vulnerability at the following site, including demonstrating how Florian's prefix/suffix patch provides no protection:
>>> You do realize that your setuid program is patently unsafe, right? Say:
>>> $ echo -e '#!/bin/sh\necho pwn3d' >date;chmod 755 date;PATH=.:$PWD
>>> ../setuid_program
>>> pwn3d
>> Glad my over-simplified example has raised a few smirks.  Now for a slightly less simplified version:
>> putenv("PATH=/bin:/usr/bin");
>> setreuid(0, 0);
>> system("date");
> Keep going, eventually you're going to have to stop blacklisting
> variables and use execve ;-)
> $ env SHELLOPTS=xtrace PS4='$(id)' ./foo
>> But the point is I've tried to boil down a relatively complex program by studying endless strace outputs to attempt to demonstrate a real world exploit.  It wasn't actually "date" that was being called, but you get the point.
> Yes, but it's not safe to use system() or popen() from setuid
> programs, no bash patch is going to change that. In fact, bash already
> does more than most other shells by dropping privileges if euid !=
> uid, i.e. "privileged mode".
>> In the past, i.e. pre-Shellshock, the above code may have raised eyebrows, but as PATH was sanitised it would have passed numerous security audits.
> No, it's not safe to use system() or popen() in this context.
> Tavis.
I believe the term following this is 'Mansplained'

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