Date: Tue, 30 Sep 2014 17:35:21 +0000 From: Zach Wikholm <zwikholm@...i.net> To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com> 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 <me@...ardprevost.info> Sent: Tuesday, September 30, 2014 8:31 AM To: oss-security@...ts.openwall.com 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 > <mark@...seconsulting.co.uk> 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: >>>> >>>> http://technicalprose.blogspot.co.uk/2014/09/shellshock-bug-third-vulnerability.html >>> 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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