MSG_PEEK is pretty common, CVE-2016-10229 is worse than you think

Published 2017-04-13 on Drew DeVault's blog

I heard about CVE-2016-10229 earlier today. In a nutshell, it allows for arbitrary code execution via UDP traffic if userspace programs are using MSG_PEEK in their recv calls. I quickly updated my kernels and rebooted any boxes where necessary, but when I read the discussions on this matter I saw people downplaying this issue by claiming MSG_PEEK is an obscure feature.

I don’t want to be a fear monger and I’m by no means a security expert but I suspect that this is a deeply incorrect conclusion. If I understand this vulnerability right you need to drop everything and update any servers running a kernel <4.5 immediately. MSG_PEEK allows a programmer using UDP to read from the kernel’s UDP buffer without consuming the data (so subsequent reads will continue to read the same data). This immediately sounds to me like a pretty useful feature that a lot of software might use, not an obscure one.

I did quick search for software where MSG_PEEK appears in the source code somewhere. This does not necessarily mean that it’s exploitable, but should certainly raise red flags. Here’s a list of some notable software I found:

  • nginx
  • haproxy
  • curl
  • gnutls
  • jack2
  • lynx
  • plex (and kodi/xbmc)
  • busybox

I also found a few things like programming languages and networking libraries that you might expect to have MSG_PEEK if only to provide that functionality to programmers leveraging them. I didn’t investigate too deeply into whether or not that was the case or if this software is using the feature in a less apparent way, but in this category I found Python, Ruby, Node.js, smalltalk, octave, libnl, and socat. I used searchcode.com to find these - here’s the full search results.

Again, I’m not a security expert, but I’m definitely spooked enough to update my shit and I suggest you do so as well. Red Hat, Debian, and Ubuntu are all unaffected because of the kernel they ship. Note, however, that many cloud providers do not let you choose your own kernel. This could mean that you are affected even if you’re running a distribution like Debian. Double check it - use uname -r and update+reboot if necessary.