Feature/client firewall filtering (#2418)

* Add per-client firewall filtering

Implement server-side firewall rules to restrict client network access,
allowing administrators to enforce security policies that cannot be
bypassed by clients modifying their local configuration.

This feature addresses the limitation where "Allowed IPs" only controls
client-side routing but doesn't prevent clients from accessing networks
they shouldn't reach. The firewall rules are enforced on the server
using iptables/ip6tables and provide true access control.

Features:
- Opt-in via "Enable Per-Client Firewall" toggle in admin interface
- Per-client "Firewall Allowed IPs" field for granular control
- Support for IPs, CIDRs, and port-based filtering
- Protocol specification: TCP, UDP, or both (default)
- IPv4 and IPv6 dual-stack support
- Falls back to client's allowedIps when firewallIps is empty
- Clean separation of routing (allowedIps) from security (firewallIps)

Supported formats:
- 10.10.0.3 (single IP)
- 10.10.0.0/24 (CIDR range)
- 192.168.1.5:443 (IP with port, both TCP+UDP)
- 192.168.1.5:443/tcp (IP with specific protocol)
- [2001:db8::1]:443 (IPv6 with port)

Implementation:
- New database columns: firewall_enabled (interfaces), firewall_ips (clients)
- Migration 0003_add_firewall_filtering for schema updates
- firewall.ts utility for iptables chain management (WG_CLIENTS chain)
- Integration into WireGuard.ts for automatic rule application
- UI components with conditional rendering based on firewall toggle

Technical details:
- Uses custom WG_CLIENTS iptables chain for isolation
- Rebuild strategy: flush and recreate all rules on config save
- Mutex protection via rebuildInProgress/rebuildQueued flags
- Graceful cleanup when firewall is disabled
- No new dependencies (uses existing is-ip, is-cidr packages)

* added Comprehensive documentation in README and docs/ for firewall
filtering

* validate firewall IPs

* check for iptables before enabling the firewall and inform the user if
it is missing

* updated firewall docs

* fix imports

* remove extra import

* Document all allowed IP/cidr/port/proto combinations that are allowed
and check on save

* add note on firewall being experimental and how to opt a single client
out of the firewall.

* cleanup more imports

* add tests

* Fix firewall IPv6 validation and test expectations

Updated validation to correctly handle plain and bracketed IPv6 addresses, and fixed test to expect string from schema instead of object.

* added comments to firewall rules and updated tests

* fix auto-import

* fix typescript errors

* recreate sql migrations and rebase

* improve tests, typechecking, documentation

* fix formatting, fix types

* improve type

* added note for including host's IP in client firewall

* updated language to include cidr and protocol options

* another language update

* refer to docs for firewall allowed IPs

---------

Co-authored-by: Bernd Storath <999999bst@gmail.com>

docs/content/faq.md

@@ -6,6 +6,20 @@ hide:
 
 Here are some frequently asked questions or errors about `wg-easy`. If you have a question that is not answered here, please feel free to open a discussion on GitHub.
 
+## How do I restrict client access to specific networks or servers?
+
+Use the **Per-Client Firewall** feature to enforce server-side restrictions on what each client can access.
+
+**Requirements:** This feature requires `iptables` (and `ip6tables` for IPv6) to be installed on the host system.
+
+1. Enable "Per-Client Firewall" in **Admin Panel → Interface**
+2. Edit a client and configure "Firewall Allowed IPs"
+3. Specify which destinations the client should be allowed to access
+
+Unlike "Allowed IPs" which only controls client-side routing, firewall rules are enforced by the server and cannot be bypassed.
+
+See the [Admin Panel Guide](guides/admin/#per-client-firewall) and [Client Guide](guides/clients/#firewall-allowed-ips) for detailed configuration.
+
 ## Error: WireGuard exited with the error: Cannot find device "wg0"
 
 This error indicates that the WireGuard interface `wg0` does not exist. This can happen if the WireGuard kernel module is not loaded or if the interface was not created properly.

docs/content/guides/admin.md

@@ -2,4 +2,42 @@
 title: Admin Panel
 ---
 
-TODO
+## Interface Settings
+
+### Per-Client Firewall
+
+Enable server-side firewall filtering to enforce network access restrictions per client.
+
+When enabled, each client can have custom "Firewall Allowed IPs" configured that restrict which destinations they can access through the VPN. These restrictions are enforced by the server using iptables/ip6tables and cannot be bypassed by the client.
+
+/// warning | Experimental Feature
+
+This feature is currently experimental. While functional, it should be thoroughly tested in your environment before relying on it for production security requirements. Always verify that firewall rules are working as expected using test traffic or by manually inspecting the rules.
+
+///
+
+**Requirements:**
+
+- `iptables` must be installed on the host system
+- `ip6tables` must be installed if IPv6 is enabled (default)
+- The feature cannot be enabled if these tools are not available
+
+/// note
+Most Linux distributions include iptables by default. If you're running in a minimal container environment, you may need to install the `iptables` package on the host system.
+///
+
+**Enable this feature if you want to:**
+
+- Restrict certain clients to only access specific servers or networks
+- Prevent clients from accessing the internet while allowing LAN access
+- Enforce port-based restrictions (e.g., only allow HTTP/HTTPS)
+- Separate routing configuration from security enforcement
+
+**How it works:**
+
+1. Enable "Per-Client Firewall" in Admin Panel → Interface
+2. Edit any client to see the new "Firewall Allowed IPs" field
+3. Specify allowed destinations (IPs, subnets, ports) for that client
+4. Server enforces these rules automatically
+
+See [Edit Client → Firewall Allowed IPs](../clients/#firewall-allowed-ips) for detailed configuration syntax and examples.

docs/content/guides/clients.md

@@ -19,7 +19,58 @@ Which IPs will be routed through the VPN.
 
 This will not prevent the user from modifying it locally and accessing IP ranges that they should not be able to access.
 
-Use firewall rules to prevent access to IP ranges that the user should not be able to access.
+Use the Firewall Allowed IPs feature to prevent access to IP ranges that the user should not be able to access.
+
+## Firewall Allowed IPs
+
+/// note | Attention
+
+This field only appears when **Per-Client Firewall** is enabled in the Admin Panel → Interface settings.
+
+///
+
+Server-side firewall rules that restrict which destinations the client can access, regardless of their local configuration.
+
+Unlike "Allowed IPs" which only controls routing on the client side, these rules are enforced by the server using iptables/ip6tables and cannot be bypassed by the client.
+
+**Supported Formats:**
+
+- `10.10.0.3`, `2001:db8::1` - Allow access to a single IP address
+- `10.10.0.0/24`, `2001:db8::/32` - Allow access to an entire subnet
+- `192.168.1.5:443` - Allow access to specific port (TCP+UDP)
+- `192.168.1.5:443/tcp` - Allow access to specific port (TCP only)
+- `192.168.1.5:443/udp` - Allow access to specific port (UDP only)
+- `10.10.0.0/24:443` - Allow access to an entire subnet on a specific port (TCP+UDP)
+- `10.10.0.0/24:443/tcp` - Allow access to an entire subnet on a specific port (TCP only)
+- `10.10.0.0/24:443/udp` - Allow access to an entire subnet on a specific port (UDP only)
+- `[2001:db8::1]:443` - IPv6 address with port (brackets required)
+- `[2001:db8::/32]:443/tcp` - IPv6 CIDR with port and protocol
+
+/// warning | Invalid Formats
+
+Protocol specifiers (`/tcp` or `/udp`) require a port number. The following formats are **not supported** and will result in an error:
+
+- `10.10.0.3/tcp` (use `10.10.0.3:443/tcp` instead)
+- `10.10.0.0/24/udp` (use `10.10.0.0/24:53/udp` instead)
+
+///
+
+**Behavior:**
+
+- **Empty**: Falls back to the client's "Allowed IPs" setting
+- **Specified**: Only listed destinations are accessible (allow-only, everything else is blocked)
+- **Disable for specific client**: To disable firewall filtering for a single client while keeping it enabled for others, add `0.0.0.0/0, ::/0` to allow all traffic
+
+/// note
+To allow clients to reach the VPN server itself (e.g. for DNS), include the server's VPN address in the firewall allowed IPs.
+///
+
+**Use Case Examples**:
+
+- Allow only specific servers: `10.10.0.5`
+- Allow only internal network: `10.10.0.0/24, 192.168.1.0/24`
+- Allow only web browsing: `0.0.0.0/0:80, 0.0.0.0/0:443, [::/0]:80, [::/0]:443`
+- Block internet, allow LAN: Leave "Allowed IPs" as `0.0.0.0/0, ::/0` but set Firewall IPs to `10.0.0.0/8, 192.168.0.0/16`
 
 ## Server Allowed IPs