How to block certain application from access the internet connection ?

On macOS, you can block an application from accessing the internet using a few different methods.

Below are three effective approaches:

• using the built-in Firewall and
• using Little Snitch (a third-party tool).
• a manual method with pfctl for advanced users.

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Method 1: Using macOS Built-in Firewall

The macOS Firewall (Application Layer Firewall, or ALF) allows you to block specific apps from accessing the internet.

1-Enable the Firewall:

• Go to System Settings (or System Preferences on older macOS versions) > Security & Privacy > Firewall tab.
• Click the lock icon in the bottom left, enter your admin password, and turn the Firewall On.

2- Configure App Blocking:

• Click Firewall Options (or “Options” depending on your macOS version).
• By default, the Firewall allows all apps unless explicitly blocked.
• Click the “+” button to add an application.
• Browse to the app you want to block (usually in /Applications), select it, and click Add.
• In the list, set the app’s rule to “Block incoming connections”. (Note: This doesn’t block outgoing connections by default—see below for outgoing traffic.)

3- Block Outgoing Connections (Optional):

• The built-in Firewall primarily manages incoming connections. To block outgoing connections, you’ll need a third-party tool like Little Snitch (Method 2) or a custom pf configuration (Method 3).

4- Test the Block:

• Launch the app and try to access the internet. Incoming connections should be blocked. For full isolation, use Method 2 or 3.

This video describes the whole process: –

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Method 2: Using Little Snitch (Third-Party Tool)

Little Snitch is a powerful firewall that gives you granular control over both incoming and outgoing connections.

1- Install Little Snitch:

• Download and install Little Snitch from its official website (it’s a paid app with a free trial).

2- Set Up Rules:

• Open Little Snitch Configuration.
• Find the application in the list (or launch the app, and it’ll appear when it tries to connect).
• Create a rule:
  • Select the app, click New Rule, and choose Deny for “Any Connection” (or specify domains/ports if you want partial blocking).
  • Set the rule to apply to Outgoing Connections, Incoming Connections, or both.

3- Apply and Test:

• Save the rule, and Little Snitch will enforce it immediately.
• Test the app to confirm it can’t access the internet.

Pros: Easy to use, blocks both incoming and outgoing traffic, and offers real-time monitoring.
Cons: Not free (costs around $45 for a single license).

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Method 3: Using pfctl (Advanced Manual Method)

For advanced users, macOS includes pf (Packet Filter), a low-level firewall that can block both incoming and outgoing traffic.

1- Enable pf:

• Open Terminal and check if pf is enabled:
  sudo pfctl -s info
• If it’s not enabled, turn it on:
  sudo pfctl -E

2- Create a Configuration File:

• Create a custom pf rules file (e.g., block_app.conf) in a location like ~/Desktop:
  sudo nano ~/Desktop/block_app.conf
• Add rules to block the app. For example, to block an app called MyApp.app: block drop out quick from any to any proto tcp from (MyApp) to any block drop out quick from any to any proto udp from (MyApp) to any
  • Replace MyApp with the exact process name (check this in Activity Monitor while the app is running).

3- Load the Rules:

• Test your rules:
  sudo pfctl -f ~/Desktop/block_app.conf
• Apply them:
  sudo pfctl -e -f ~/Desktop/block_app.conf

4- Make Rules Persistent (Optional):

• To load the rules on boot, edit the system pf config file (/etc/pf.conf) or create a launch daemon, but this is complex and requires caution.

5- Test and Disable (if Needed):

• Test the app to ensure it’s blocked.
• To disable: sudo pfctl -d.

Pros: Free, powerful, and built into macOS.
Cons: Requires technical knowledge and doesn’t persist across reboots without extra setup.

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Which Method to Choose?

• Firewall: Best for simple incoming connection blocks, free, built-in.
• Little Snitch: Ideal for full control (incoming + outgoing), user-friendly but paid.
• pfctl: Free and advanced, but requires command-line skills.