--- a/mod_net_proxy/README.markdown	Wed Mar 28 19:03:10 2018 +0200
+++ b/mod_net_proxy/README.markdown	Wed Mar 28 20:47:41 2018 +0200
@@ -37,22 +37,40 @@
 
 ```lua
 --[[
-	Hint: While you can manually override the ports this module is listening on with
-	the "proxy_ports" directive, it is highly recommended to not set it and instead
-	only configure the appropriate mappings with "proxy_port_mappings", which will
-	automatically start listening on all mapped ports.
-]]--
-
+  Maps TCP ports to a specific Prosody network service. Further information about
+  available service names can be found further down below in the module documentation.
+]]-- 
 proxy_port_mappings = {
 	[15222] = "c2s",
 	[15269] = "s2s"
 }
+
+--[[
+  Specifies a list of trusted hosts or networks which may use the PROXY protocol
+  If not specified, it will default to: 127.0.0.1, ::1 (local connections only)
+  An empty table ({}) can be configured to allow connections from any source.
+  Please read the module documentation about potential security impact.
+]]-- 
+proxy_trusted_proxies = {
+	"192.168.10.1",
+	"172.16.0.0/16"
+}
+
+--[[
+  While you can manually override the ports this module is listening on with
+  the "proxy_ports" directive, it is highly recommended to not set it and instead
+  only configure the appropriate mappings with "proxy_port_mappings", which will
+  automatically start listening on all mapped ports.
+
+  Example: proxy_ports = { 15222, 15269 }
+]]--
 ```
 
 The above example configuration, which needs to be placed in the global section,
-would listen on both tcp/15222 and tcp/15269. All incoming connections to these ports
-have to be initiated by a PROXYv1 or PROXYv2 sender and will get mapped to the
-configured service name after initializating the connection.
+would listen on both tcp/15222 and tcp/15269. All incoming connections have to 
+originate from trusted hosts/networks (configured by _proxy_trusted_proxies_) and
+must be initiated by a PROXYv1 or PROXYv2 sender. After processing the PROXY
+protocol, those connections will get mapped to the configured service name.
 
 Please note that each port handled by _mod_net_proxy_ must be mapped to another
 service name by adding an item to _proxy_port_mappings_, otherwise a warning will

--- a/mod_net_proxy/mod_net_proxy.lua	Wed Mar 28 19:03:10 2018 +0200
+++ b/mod_net_proxy/mod_net_proxy.lua	Wed Mar 28 20:47:41 2018 +0200
@@ -67,9 +67,15 @@
 };
 local PROTO_HANDLER_STATUS = { SUCCESS = 0, POSTPONE = 1, FAILURE = 2 };
 
+-- Configuration Variables
+local config_mappings = module:get_option("proxy_port_mappings", {});
+local config_ports = module:get_option_set("proxy_ports", {});
+local config_trusted_proxies = module:get_option_set("proxy_trusted_proxies", {"127.0.0.1", "::1"});
+
 -- Persistent In-Memory Storage
 local sessions = {};
 local mappings = {};
+local trusted_networks = set.new();
 
 -- Proxy Data Methods
 local proxy_data_mt = {}; proxy_data_mt.__index = proxy_data_mt;
@@ -314,10 +320,37 @@
 	return service_listener.onincoming(conn, session.buffer);
 end
 
+local function is_trusted_proxy(conn)
+	-- If no trusted proxies were configured, trust any incoming connection
+	-- While this may seem insecure, the module defaults to only trusting 127.0.0.1 and ::1
+	if trusted_networks:empty() then
+		return true;
+	end
+
+	-- Iterate through all trusted proxies and check for match against connected IP address
+	local conn_ip = ip.new_ip(conn:ip());
+	for trusted_network in trusted_networks:items() do
+		if ip.match(trusted_network.ip, conn_ip, trusted_network.cidr) then
+			return true;
+		end
+	end
+
+	-- Connection does not match any trusted proxy
+	return false;
+end
+
 -- Network Listener Methods
 local listener = {};
 
 function listener.onconnect(conn)
+	-- Check if connection is coming from a trusted proxy
+	if not is_trusted_proxy(conn) then
+		conn:close();
+		module:log("warn", "Dropped connection from untrusted proxy: %s", conn:ip());
+		return;
+	end
+
+	-- Initialize session variables
 	sessions[conn] = {
 		handler = nil;
 		buffer = nil;
@@ -388,9 +421,19 @@
 
 listener.ondetach = listener.ondisconnect;
 
+-- Parse trusted proxies which can either contain single hosts or networks
+if not config_trusted_proxies:empty() then
+	for trusted_proxy in config_trusted_proxies:items() do
+		local network = {};
+		network.ip, network.cidr = ip.parse_cidr(trusted_proxy);
+		trusted_networks:add(network);
+	end
+else
+	module:log("warn", "No trusted proxies configured, all connections will be accepted - this might be dangerous");
+end
+
 -- Process all configured port mappings and generate a list of mapped ports
 local mapped_ports = {};
-local config_mappings = module:get_option("proxy_port_mappings", {});
 for port, mapping in pairs(config_mappings) do
 	table.insert(mapped_ports, port);
 	mappings[port] = {
@@ -400,7 +443,6 @@
 end
 
 -- Log error message when user manually specifies ports without configuring the necessary port mappings
-local config_ports = module:get_option_set("proxy_ports", {});
 if not config_ports:empty() then
 	local missing_ports = config_ports - set.new(mapped_ports);
 	if not missing_ports:empty() then