diff --git a/internal/configuration/settings/errors.go b/internal/configuration/settings/errors.go
index c11b646a..d3ebf02c 100644
--- a/internal/configuration/settings/errors.go
+++ b/internal/configuration/settings/errors.go
@@ -7,7 +7,8 @@ var (
 	ErrControlServerPrivilegedPort     = errors.New("cannot use privileged port without running as root")
 	ErrCountryNotValid                 = errors.New("the country specified is not valid")
 	ErrFilepathMissing                 = errors.New("filepath is missing")
-	ErrFirewallZeroPort                = errors.New("cannot have a zero port to block")
+	ErrFirewallZeroPort                = errors.New("cannot have a zero port")
+	ErrFirewallPublicOutboundSubnet    = errors.New("outbound subnet is public")
 	ErrHostnameNotValid                = errors.New("the hostname specified is not valid")
 	ErrISPNotValid                     = errors.New("the ISP specified is not valid")
 	ErrMinRatioNotValid                = errors.New("minimum ratio is not valid")
diff --git a/internal/configuration/settings/firewall.go b/internal/configuration/settings/firewall.go
index 466072d2..9d8b61dd 100644
--- a/internal/configuration/settings/firewall.go
+++ b/internal/configuration/settings/firewall.go
@@ -26,6 +26,12 @@ func (f Firewall) validate() (err error) {
 		return fmt.Errorf("input ports: %w", ErrFirewallZeroPort)
 	}
 
+	for _, subnet := range f.OutboundSubnets {
+		if !subnet.Addr().IsPrivate() {
+			return fmt.Errorf("%w: %s", ErrFirewallPublicOutboundSubnet, subnet)
+		}
+	}
+
 	return nil
 }
 
diff --git a/internal/configuration/settings/firewall_test.go b/internal/configuration/settings/firewall_test.go
new file mode 100644
index 00000000..7a4a4e8f
--- /dev/null
+++ b/internal/configuration/settings/firewall_test.go
@@ -0,0 +1,76 @@
+package settings
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_Firewall_validate(t *testing.T) {
+	t.Parallel()
+
+	testCases := map[string]struct {
+		firewall   Firewall
+		errWrapped error
+		errMessage string
+	}{
+		"empty": {},
+		"zero_vpn_input_port": {
+			firewall: Firewall{
+				VPNInputPorts: []uint16{0},
+			},
+			errWrapped: ErrFirewallZeroPort,
+			errMessage: "VPN input ports: cannot have a zero port",
+		},
+		"zero_input_port": {
+			firewall: Firewall{
+				InputPorts: []uint16{0},
+			},
+			errWrapped: ErrFirewallZeroPort,
+			errMessage: "input ports: cannot have a zero port",
+		},
+		"unspecified_outbound_subnet": {
+			firewall: Firewall{
+				OutboundSubnets: []netip.Prefix{
+					netip.MustParsePrefix("0.0.0.0/0"),
+				},
+			},
+			errWrapped: ErrFirewallPublicOutboundSubnet,
+			errMessage: "outbound subnet is public: 0.0.0.0/0",
+		},
+		"public_outbound_subnet": {
+			firewall: Firewall{
+				OutboundSubnets: []netip.Prefix{
+					netip.MustParsePrefix("1.2.3.4/32"),
+				},
+			},
+			errWrapped: ErrFirewallPublicOutboundSubnet,
+			errMessage: "outbound subnet is public: 1.2.3.4/32",
+		},
+		"valid_settings": {
+			firewall: Firewall{
+				VPNInputPorts: []uint16{100, 101},
+				InputPorts:    []uint16{200, 201},
+				OutboundSubnets: []netip.Prefix{
+					netip.MustParsePrefix("192.168.1.0/24"),
+					netip.MustParsePrefix("10.10.1.1/32"),
+				},
+			},
+		},
+	}
+
+	for name, testCase := range testCases {
+		testCase := testCase
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			err := testCase.firewall.validate()
+
+			assert.ErrorIs(t, err, testCase.errWrapped)
+			if testCase.errWrapped != nil {
+				assert.EqualError(t, err, testCase.errMessage)
+			}
+		})
+	}
+}