Date: Wed, 13 Feb 2019 01:53:10 -0800 From: EJ Campbell <ejc3@...izonmedia.com> To: "cyphar@...har.com" <cyphar@...har.com>, oss-security@...ts.openwall.com Subject: Re: CVE-2019-5736: runc container breakout exploit code While fixing docker / runc is clearly the right fix, would using chattr -i on runc be a quick mitigation for the issue? I believe that will prevent the file from being overwritten by the exploit and Etienne Stalmans verified that it helped: https://twitter.com/_staaldraad/status/1095354945073754112 (Note I tried top posting this to mailing list and it didn’t work). EJ On Wed, Feb 13, 2019 at 1:32 AM Aleksa Sarai <cyphar@...har.com> wrote: > Someone outside of the embargo has posted a PoC of the exploit for > CVE-2019-5736 (which is related though not using the same vector). > Since the original researchers have posted a blog post explaining the > exploit in some detail, I've decided to post the exploit code early > -- since the cat is out of the bag anyway. > > CVE-2019-5736.tar.xz has the exploit code and an explanation of how to > use it. Our exploit code uses shared libraries, but you can create a > similar exploit by doing something like (thanks to Darren Shepherd from > Rancher Labs for pointing this out): > > 1. Run a script with a #!-line of "#!/proc/self/exe events" which will > run "runc events" (which blocks for long enough). > 2. A malicious process then opens /proc/$pid/exe (this is now allowed > because the non-dumpable bit was cleared on execve). > 3. Kill "runc events" and then re-open the exe fd read-write using the > "/proc/self/fd/..." trick. > > This is basically what  does -- but it does come with the downside > that you can't craft a malicious image that does this, you need to have > a separate program already running in the container and then attack > "docker exec". > > As discussed in the previous mail, this exploit code also impacts LXC > (and several other runtimes have contacted me to say that they are also > vulnerable -- I would suggest that runtimes should ask to join > <security-announce@...ncontainers.org>). > > : https://github.com/feexd/pocs/blob/master/CVE-2019-5736/exploit.c > : > https://blog.dragonsector.pl/2019/02/cve-2019-5736-escape-from-docker-and.html > > -- > Aleksa Sarai > Senior Software Engineer (Containers) > SUSE Linux GmbH > <https://www.cyphar.com/> >
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