So you built a beautiful self-hosted Assetto Corsa Competizione dedicated server. Custom liveries, tight competitive sessions, a small but loyal community. Then one day the lobby just… dies. Players can’t connect, pings spike into oblivion, and your server host is emailing you about abnormal traffic. Welcome to the world of QUIC-based DTLS amplification DDoS attacks.
What’s Actually Happening to Your Server
QUIC uses UDP port 443, and the DTLS handshake inside it can be weaponized. Attackers send spoofed ClientHello packets to your server, and if your server isn’t enforcing HelloVerifyRequest, it responds with a much larger payload. That response gets fire-hosed at a victim — or just overwhelms your own uplink. It’s an amplification attack hiding inside a protocol most firewalls don’t scrutinize closely.
ACC’s dedicated server listens on UDP for game traffic, and because port 443 is often treated as “trusted” by network policies, this vector slips through surprisingly often. The result is lag, crashes, and frustrated sim racers rage-quitting forever.
Layer 1: nftables Rate Limiting on UDP Port 443
Your first line of defense is local. On a Linux host, nftables gives you surgical control over traffic. Add a rule that rate-limits incoming UDP on port 443 to a sensible threshold — something that allows legitimate QUIC handshakes but slams the door on floods.
A Quick nftables Example
Inside your nftables ruleset, you can use limit rate with a burst allowance to catch spikes without blocking real players. Something like 100 packets per second with a burst of 200 is a reasonable starting point, but tune it based on your actual player count. Test before going live on a race night.
Layer 2: Enforce DTLS HelloVerifyRequest
This is the underrated fix. DTLS is designed to include a cookie-based verification step precisely to prevent amplification. If your stack or any upstream proxy isn’t enforcing HelloVerifyRequest, you’re handing attackers a megaphone.
Check your DTLS implementation or any middleware you’re using. If you’re running a custom relay or a game proxy, make absolutely sure cookie verification is enabled. It’s often disabled by default for “convenience” — which is exactly why attackers love it.
Layer 3: Imperva DDoS Protection as a BGP Scrubbing Layer
Local rules only go so far. When volumetric attacks hit, your uplink saturates before nftables even sees the packet. That’s where upstream scrubbing shines. Imperva’s DDoS Protection uses BGP route announcement to divert your traffic through their scrubbing centers, stripping attack traffic before it ever touches your server.
For a self-hosted setup, this means working with your ISP or hosting provider to announce your IP space through Imperva during an attack event — or on an always-on basis if you’re a regular target. It’s enterprise-grade protection that’s more accessible than most people think.
Practical Tips Before You Get Hit
Audit your firewall rules today, not during an active attack. Document your normal UDP traffic baseline so anomalies are obvious. Keep nftables rules version-controlled. And seriously — test your mitigation before your next race event, not during it.
You Don’t Have to Figure This Out Alone
If you’re running competitive ACC servers and want a hardened setup from the ground up, professional DDoS protection consulting is available for exactly this kind of infrastructure. Sometimes a single conversation saves weeks of painful trial and error.
If you’re under attack right now, don’t wait — open a support ticket immediately. Every minute of downtime is another player who might not come back. Get help, get protected, and get back on track.
