Running Wireshark in a jail/sandbox

Abstract

Firejail is a powerful tool which can be use to sandboxing lot of applications. By default Firejail provides profiles for Chrome, Firefox, Telegram and other famous applications. Wireshark is still missing.

We want to limit the interfaces a user can sniff. To be more specific, we want users capture from bridges interfaces only.

Installing Firejail

On Ubuntu 16.04 Firejail is available universe repository:

# apt-get -y install firejail

All profiles are stored under /etc/firejail/*.profile. We can run a bash using a generic profile:

$ firejail --profile=/etc/firejail/generic.profile bash

Wireshark under Firejail

Wireshark is a little bit more complicated:

  • Wireshark call dumpcap to capture packets without root privileges;
  • dumpcap has few capabilities so every user in the wireshark group has some advanced privileges:
# getcap /usr/bin/dumpcap
/usr/bin/dumpcap = cap_net_admin,cap_net_raw+eip

Let’s add a new profile:

# cat /etc/firejail/wireshark-gtk.profile
# Wireshark profile

private-bin bash,ls,wireshark-gtk,reordercap,dumpcap,editcap,rawshark,mergecap,text2pcap,capinfos
private-dev
private-etc fonts,group,gtk-3.0,hosts,machine-id,wiresharck
private-tmp

noblacklist /bin
noblacklist /dev
noblacklist /etc
noblacklist /home
noblacklist /lib
noblacklist /lib64
noblacklist /sys
noblacklist /tmp
noblacklist /usr
blacklist /*

caps.drop all
netfilter
noroot
seccomp
shell none

The above profiles:

  • maps all bin and sbin directories importing few binaries;
  • maps an almost empty /dev directory;
  • maps an almost empty /etc directory;
  • maps an empty /tmp directory;
  • blacklists (disables) all directories except the one required by Wireshark;
  • enforces more the jail.

Users must not be part of the wireshark group, or they’ll get privileges to captures from any interface. Now add at least one rule for sudo:

@brcapture ALL=(root) NOPASSWD: /usr/bin/dumpcap -s0 -i br0 -P -w -

Mind that dumpcap can capture from multiple interfaces at the same time, so you should not use the * symbol,

From any user in the brcapture group you can now capture packets without any risk;

$ sudo /usr/bin/dumpcap -s0 -i br0 -P -w - | firejail wireshark-gtk -n -k -i -

Wireshak inside a jail

If the user stop the capture from the Wireshark UI and try to start the capture on a different interface, he will get a You don't have permission to capture on that device error. Moreover if the user will try to browse the filesystem, he will get a Could not read the content error on most of the directories.

To check what is inside the Wireshark jail, just try to start a bash using that profile:

$ firejail --profile=/etc/firejail/wireshark-gtk.profile bash

For example you will see an almost empty /etc:

$ ls /etc/
fonts  group  gtk-3.0  hosts  machine-id

References

Posted on 01 Dec 2016.
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