FortiGate 70F Deep Packet Inspection CPU Saturation under QUIC / HTTP/3 Traffic
High-concurrency UDP 443 QUIC and HTTP/3 streams bypass the SOC4 CP9 content processor hardware cryptographic offload, thrashing host CPU cores inside the wad worker processes and driving total CPU usage to 100% on FortiGate 40F, 60F, and 70F models.
Technical Root Cause Analysis
Modern web browsers (Google Chrome, Microsoft Edge, Mozilla Firefox) and cloud services (YouTube, Cloudflare, Google Cloud) prioritize HTTP/3 using the QUIC protocol over UDP port 443. While traditional HTTPS over TCP port 443 leverages the Fortinet CP9 content processor for hardware-accelerated TLS 1.2/1.3 session setup and AES crypto decryption, the integrated CP9 in SOC4 entry appliances lacks hardware state machines for UDP-encapsulated QUIC TLS 1.3 packets.
When Deep Packet Inspection (DPI) or Web Filtering is enforced on firewall policies matching all service ports or UDP port 443, the FortiOS kernel punts all QUIC streams to user-space wad worker daemons. Because each QUIC packet requires software decryption, reassembly, stream multiplexing, and loss detection on general-purpose CPU cores, CPU utilization immediately saturates at 99–100%. This induces high packet latency, dropped sessions, and GUI/SSH management timeouts.
Affected Hardware & Blast Radius Matrix
| Appliance Platform | Processor Architecture | QUIC Hardware Acceleration | Impact under Heavy QUIC |
|---|---|---|---|
| FortiGate 40F / 60F | SOC4 (1.2 GHz Quad-Core) | No (Software Fallback) | Critical: 100% CPU lock, management hang |
| FortiGate 70F | SOC4 (1.5 GHz Quad-Core) | No (Software Fallback) | High: 95–100% CPU, high transit jitter |
| FortiGate 100F – 200F | SOC4 + Dedicated CP9 | Partial (Higher CPU headroom) | Moderate: Elevated CPU (60–75%) |
| FortiGate 400F+ (NP7/CP9) | Enterprise Multi-Core | Supported (Flow/CP9 offload) | Normal: Low CPU utilization (<25%) |
Software Scope: Affects FortiOS 7.2.4 through 7.2.7 and 7.4.0 through 7.4.2 when Deep SSL Inspection or Proxy Web Filtering profiles inspect UDP port 443 without QUIC protocol suppression.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these diagnostic commands to verify real-time per-core CPU utilization, identify the responsible WAD processes, and count active UDP 443 sessions:
Diagnostic Commands
# 1. Check real-time top CPU processes (press 'q' to exit)
diagnose sys top 2 5
# 2. Inspect active UDP port 443 session count
diagnose firewall session full-stat | grep "udp 443"
# 3. View per-core CPU utilization statistics
diagnose sys mpstat 2
# 4. Check WAD proxy worker utilization and active connection table
diagnose test application wad 2Remediation & Workaround Steps (Teaser Preview)
Follow the non-disruptive remediation guide in the Ferrite interactive platform to restore immediate line-rate throughput:
Frequently Asked Questions
Entry-level SOC4 models (40F, 60F, 70F) do not support hardware cryptographic offload for UDP-based TLS 1.3 packets. The software fallback in the WAD daemon consumes 100% of host CPU cycles during high video and web traffic.
No. RFC 9000 mandates that web browsers fall back to TCP TLS 1.2/1.3 within milliseconds when QUIC is blocked. Users experience seamless browsing with line-rate performance.
Fortinet and Ferrite recommend flow-based inspection mode on all 2GB and 4GB desktop units to avoid user-space proxy memory pressure and CPU saturation.