Copyright © 2005, 2010, 2013 Thomas M. Eastep
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2020/02/16
Shorewall includes support for UPnP (Universal Plug and Play) using linux-igd (http://linux-igd.sourceforge.net). UPnP is required by a number of popular applications including MSN IM.
Warning
From a security architecture viewpoint, UPnP is a disaster. It assumes that:
All local systems and their users are completely trustworthy.
No local system is infected with any worm or trojan.
If either of these assumptions are not true then UPnP can be used to totally defeat your firewall and to allow incoming connections to arbitrary local systems on any port whatsoever. In short: USE UPnP AT YOUR OWN RISK.
Important
Shorewall and linux-igd implement a UPnP Internet Gateway Device. It will not allow clients on one LAN subnet to access a UPnP Media Server on another subnet.
In /etc/upnpd.conf, you will want:
create_forward_rules = yes prerouting_chain_name = UPnP forward_chain_name = forwardUPnP
In /etc/shorewall/interfaces, you need the
'upnp' option on your external interface.
Example:
#ZONE INTERFACE OPTIONS
net eth1 dhcp,routefilter,tcpflags,upnpIf your loc->fw policy is not ACCEPT then you need this rule:
#ACTION SOURCE DEST allowinUPnP loc $FW
You MUST have this rule:
#ACTION SOURCE DEST forwardUPnP net loc
You must also ensure that you have a route to 224.0.0.0/4 on your internal (local) interface as described in the linux-igd documentation.
Note
The init script included with the Debian linux-idg package adds this route during start and deletes it during stop.
Caution
Shorewall versions prior to 4.4.10 do not retain the dynamic rules added by linux-idg over a shorewall restart.
If your firewall->loc policy is not ACCEPT, then you also need to allow UDP traffic from the fireawll to the local zone.
ACCEPT $FW loc udp - <dynamic port range>The dynamic port range is obtained by cat /proc/sys/net/ip_local_port_range.
It is sometimes desirable to run UPnP-enabled client programs like Transmission (BitTorrent client) on a Shorewall-protected system. Shorewall provides support for UPnP client access in the form of the upnpclient option in shorewall-interfaces (5).
The upnpclient option causes Shorewall to detect the default gateway through the interface and to accept UDP packets from that gateway. Note that, like all aspects of UPnP, this is a security hole so use this option at your own risk.
Note that when multiple clients behind the firewall use UPnP, they must configure their applications to use unique ports.
