PostUp/PreUp/PostDown/PreDown Dangerous?

[logcabin at fastmail.net]

I'm in favor of keeping the features. A competent sysadmin or netadmin should know not to put questionable material on their systems, or at the very least, try it on a test bed where it can't do any damage.

On Thu, Jun 21, 2018, at 9:41 PM, Jason A. Donenfeld wrote:
> Hey list,
> 
> wg(8) is the main WireGuard configuration tool. It takes a fairly
> strict set of inputs, and is supposed to perform acceptable input
> validation on them.
> 
> https://git.zx2c4.com/WireGuard/about/src/tools/man/wg.8
> 
> wg-quick(8), on the other and, is a dinky bash script, that is useful
> for making some common limited use cases a bit easier.
> 
> https://git.zx2c4.com/WireGuard/about/src/tools/man/wg-quick.8
> 
> wg-quick(8) has the very handy feature of allowing
> PostUp/PostDown/PreUp/PreDown directives, to execute some helpers,
> such as iptables or whatever else you want in a custom setup. These
> have proven very useful to folks. And because these allow arbitrary
> execution anyway, wg-quick(8) doesn't try very hard to do proper input
> validation either.
> 
> I just saw this nice post pointing out a problem in OpenVPN:
> https://medium.com/tenable-techblog/reverse-shell-from-an-openvpn-configuration-file-73fd8b1d38da
> 
> The same thing applies to wg-quick(8) with
> PostUp/PostDown/PreUp/PreDown. The question is how seriously we should
> take the problem presented by this blog post. Namely, you can't trust
> configuration files given to you by outside parties. Maybe you
> shouldn't reconfigure your network without inspecting what those
> reconfigurations are first. However, one could argue that code
> execution is a bit beyond networking config.
> 
> So, the question we need to ask is whether this problem is important
> enough that these useful features should be _removed_? Or if there's a
> way to make them safer? Or if it just doesn't matter that much and we
> shouldn't do anything.
> 
> Thoughts?
> 
> Jason
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