bypassing wireguard using firejail

[Sitaram Chamarty]

On Fri, May 10, 2019 at 02:06:04PM +0000, Jordan Glover wrote:
> On Friday, May 10, 2019 11:54 AM, Sitaram Chamarty <sitaramc at gmail.com> wrote:
> 
> > I am able to bypass the VPN by using firejail (which is a
> > sandbox program to run untrusted applications).
> >
> > Below, the IP addresses and domain names are fake but that
> > should not matter:
> >
> > # wg
> > interface: wg0
> > public key: ....
> > private key: (hidden)
> > listening port: 59457
> > fwmark: 0xca6c
> >
> > peer: ....
> > endpoint: 11.22.33.44:51820
> > allowed ips: 0.0.0.0/0
> > latest handshake: 41 seconds ago
> > transfer: 35.42 MiB received, 2.74 MiB sent
> >
> > $ curl zx2c4.com/ip
> > 11.22.33.44 <--- my wg VPN end point IP
> > static.44.33.22.11.elided.tld
> > curl/7.64.0
> >
> > $ firejail --net=wlp2s0 --dns=8.8.8.8 curl zx2c4.com/ip
> > 55.66.77.88 <--- my actual external IP
> > elided.hostname.myisp.in
> > curl/7.64.0
> >
> > My questions:
> >
> > 1.  I know firejail is suid root, but still... is there any way
> >     to prevent this from happening, or at least make it less
> >     trivial?
> >
> >     I'm OK with a "this is the way it is, if your untrusted app
> >     is running as root you're already toast" response; just want
> >     to make sure I'm not missing a bet here.
> >
> > 2.  I guess I don't know as much about Linux networking as I
> >     thought I knew, especially about policy routing, so I am
> >     feeling a bit lost here.
> >
> >     I would prefer not to have to learn lots of things about
> >     policy routing and so on, so I wonder if there is a simple,
> >     (wireguard-specific, if possible) explanation of how linux
> >     policy routing and iptables work behind the scenes to direct
> >     packets when wireguard is in play?
> >
> >     regards
> >     sitaram
> >
> >
> 
> This is known firejail feature[1]. If you want to prevent yourself
> from this footgun you may add "restricted-network yes" in
> /etc/firejail/firejail.config

Thanks.