The Rise of Rust in Security Appliances and Firewalls

The Silent Revolution at the Edge For years, the edge of the network — firewalls, routers, intrusion detection systems — has been dominated by C and C++. From pfSense to Cisco ASA, the low-level control and speed of C made it the default. But quietly, a new player has been rewriting this story: Rust. Today, security appliances built in Rust are moving from hobby projects to production deployments. Companies like Cloudflare, Fastly, and even defense tech startups are using Rust not just for web servers or SDKs — but for core packet inspection, filtering, and crypto pipelines. Why? Because security code can’t afford to be unsafe. Why C and C++ Started to Crack Security software is one of the most dangerous places for unsafe memory handling. Think about it: firewalls, VPN daemons, and deep packet inspection engines all handle untrusted network input — directly from the wild. For decades, we’ve been patching buffer overflows and use-after-free bugs in C-based systems like OpenSSL, iptables, and Snort. In fact, a 2019 Microsoft study showed that 70% of all security vulnerabilities were caused by memory safety issues. Rust flips that equation. “Rust doesn’t let you write insecure code by accident — and that changes everything for firewall development.” — Network Security Engineer, Fastly Edge Team The Rust Security Stack: A New Breed of Firewalls Let’s look at what this actually looks like in practice. Example: A Minimal Rust Firewall Filter Below is a toy example of a Rust-based packet filter using the pnet crate: use pnet::datalink::{self, NetworkInterface}; use pnet::packet::{ipv4::Ipv4Packet, Packet};

fn main() {

   let interfaces = datalink::interfaces();
   let interface = interfaces.into_iter()
       .find(|iface| iface.name == "eth0")
       .expect("No interface named eth0");
   let (_, mut rx) = match datalink::channel(&interface, Default::default()) {
       Ok(datalink::Channel::Ethernet(tx, rx)) => (tx, rx),
       _ => panic!("Unsupported channel type"),
   };
   while let Ok(packet) = rx.next() {
       if let Some(ipv4) = Ipv4Packet::new(packet) {
           if ipv4.get_destination() == "192.168.1.1".parse().unwrap() {
               println!("Blocked packet to internal address: {:?}", ipv4);
           }
       }
   }

} This is a safe, memory-managed packet capture and inspection loop. No malloc, no raw pointers, no segfaults. In C, this same logic would require raw socket buffers, pointer arithmetic, and manual frees — every line a potential vulnerability. Architecture: Rust at the Network Edge Here’s a simplified view of what a modern Rust-based firewall or security appliance looks like:

               ┌──────────────────────────────┐
               │  Network Interface Driver    │
               │     (DPDK / netmap / AF_XDP) │
               └──────────────┬───────────────┘
                              │
                    Zero-Copy Packet Stream
                              │
               ┌──────────────┴───────────────┐
               │  Rust Packet Processor       │
               │  (Tokio + pnet + eBPF)       │
               └──────────────┬───────────────┘
                              │
                Async Pipeline / Rules Engine
                              │
               ┌──────────────┴───────────────┐
               │   Deep Inspection Layer      │
               │ (regex + TLS + crypto crates)│
               └──────────────┬───────────────┘
                              │
                   Secure Logging & Telemetry

Why This Matters Rust’s async + zero-cost abstraction model makes it ideal for this architecture:

Tokio handles thousands of connections concurrently.
pnet or smoltcp provides low-level packet handling without unsafe overhead.
serde, regex, and ring power high-level rule parsing and cryptography.

And everything above can be audited and formally verified — something C-based daemons rarely achieve. Real-World Examples 1. Firecracker VMM (AWS) Amazon’s lightweight hypervisor for Lambda and Fargate uses Rust in its core network and device isolation layers. It’s not a firewall per se, but it acts like one: controlling network isolation between microVMs safely and deterministically. 2. Vector by Datadog A high-performance telemetry router written in Rust, Vector is now being embedded in security edge appliances to process logs and metrics securely — avoiding crashes or injection bugs. 3. Cloudflare’s Pingora A complete rewrite of their NGINX-based reverse proxy stack in Rust. It now forms the front-line defense for millions of requests per second — and with fewer CVEs. The Real Reason: Safety and Speed The usual argument is: “Rust is safe, but maybe slower.” Not anymore. Rust’s zero-cost abstractions, ownership-based concurrency, and inlining let it go toe-to-toe with C in packet parsing and routing — while staying memory safe. Benchmark studies from the NetBricks project at MIT showed that Rust-based NFV systems achieved near-native throughput — even outperforming DPDK-based C frameworks under some configurations. Code Flow: From Ethernet Frame to Decision Let’s look at a simplified flow: [ NIC RX Buffer ]

↓

[ Rust pnet packet capture ]

↓

[ Parse IP / TCP headers safely ]

↓

[ Match against filter rules (serde_json) ]

↓

[ Log or block using async channel ]

↓

[ Forward to next hop if allowed ] And you can visualize the concurrency like this: use tokio::sync::mpsc; use serde::Deserialize;

[derive(Deserialize)]

struct Rule { block_ip: String }

[tokio::main]

async fn main() {

   let (tx, mut rx) = mpsc::channel(100);
   let rules: Vec<Rule> = serde_json::from_str(r#"[{"block_ip":"10.0.0.5"}]"#).unwrap();
   tokio::spawn(async move {
       while let Some(packet) = rx.recv().await {
           if rules.iter().any(|r| packet.src_ip == r.block_ip) {
               println!("Dropped {:?}", packet);
           }
       }
   });
   tx.send(Packet { src_ip: "10.0.0.5".into() }).await.unwrap();

} This model combines asynchronous IO, memory safety, and structured rule sets — all without threads stepping on each other. Architecture Insight: Why Rust Wins in Firewalls | Feature | C/C++ | Rust | | ------------------ | --------------------------- | -------------------------- | | Memory safety | ❌ Requires audits | ✅ Compiler-enforced | | Thread safety | ❌ Manual locks | ✅ Ownership model | | Crash recovery | ⚠️ Limited | ✅ Result/Error types | | Performance | ✅ Native speed | ✅ Near-native (0-cost) | | Auditability | ⚠️ Hard to prove | ✅ Easy to verify | | Developer velocity | ⚠️ Slow for large codebases | ✅ Safe refactors & modules | The difference isn’t just theoretical — it’s operational. Rust’s borrow checker becomes part of your security model. The Future: Rust at the Network Core In 2025, we’re seeing more than just firewalls — entire network stacks in Rust:

NetBricks — NFV platform in Rust.
smoltcp — lightweight TCP/IP stack for embedded firewalls.
rust-dpdk — bindings for high-speed packet IO.
suricata-rs (experimental) — exploring Rust modules for Suricata IDS.

And as eBPF and io_uring evolve, Rust’s type safety could define a new generation of programmable network security systems — safer, faster, and maintainable. Closing Thoughts There’s something poetic about rewriting the defenders in a language that defends itself. Rust doesn’t just make firewalls faster — it makes them trustworthy. In a world where the perimeter is constantly shifting, and new exploits emerge every week, safety by design isn’t a luxury — it’s a requirement. The next-gen firewalls won’t be written in C. They’ll be written in Rust. Rust isn’t just another language for systems programming — it’s becoming the backbone of network security itself. From Cloudflare’s edge proxies to open-source packet filters, the era of memory-safe firewalls has begun — and this time, the walls don’t have cracks.