Allow/Block a Program

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Introduction

This is a single method that allows/blocks an executable through the firewall. I wrote this method for one of my applications and decided to post here for everyone's good.

Background

The idea here is to use the NetFwTypeLib located in (C:\windows\system32\FirewallAPI.dll) to add a rule that allows/blocks the executable with the specified path from establishing a connection of any type.

Using the Code

First, the FirewallAPI.dll must be added to references and NetFwTypeLib to usings.

Then, you can use the following method:

/// <summary>
/// Adds or removes a firewall rule.
/// </summary>
/// <param name="path">The path to the executable.</param>
/// <param name="d">The affected connection type.</param>
/// <param name="fwaction">Rule action.</param>
/// <param name="action">"Add (1) or 
/// remove (0) the specified rule."</param>
private void FWRule(string path, NET_FW_RULE_DIRECTION_ d, 
		NET_FW_ACTION_ fwaction, string action)
{
    try
    {
        INetFwRule firewallRule = (INetFwRule)Activator.CreateInstance(
        Type.GetTypeFromProgID("HNetCfg.FWRule"));
        firewallRule.Action = fwaction;
        firewallRule.Enabled = true;
        firewallRule.InterfaceTypes = "All";
        firewallRule.ApplicationName = path;
        firewallRule.Name = "CSwitch: " + Path.GetFileName(path);
        INetFwPolicy2 firewallPolicy = (INetFwPolicy2)Activator.CreateInstance
        (Type.GetTypeFromProgID("HNetCfg.FwPolicy2"));
            firewallRule.Direction = d;
            if (action == "1") firewallPolicy.Rules.Add(firewallRule);
            else firewallPolicy.Rules.Remove(firewallRule.Name);
    }
    catch (Exception ex) { MessageBox.Show(ex.Message, "ERROR"); }}} }   

Example

FWRule(@"C:\test.exe", NET_FW_RULE_DIRECTION_.NET_FW_RULE_DIR_OUT, 
NET_FW_ACTION_.NET_FW_ACTION_BLOCK, "1"); 

This will block test.exe from making any outgoing connections.

Points of Interest

While writing this, I noticed that trying to use the same INetFwRule variable multiple times could throw a CATASTROPHIC FAILURE (Access Denied) exception.