FortiGate 90G SP5 Hardware Cryptographic Acceleration Failure on AES-GCM-256

Technical Root Cause Analysis

The FortiGate 90G architecture introduces Fortinet's 7nm SP5 processor, combining RISC-V compute cores with hardware encryption offload engines capable of accelerating IPsec at up to 25 Gbps line rate.

In FortiOS 7.4.2 NPI builds, an initialization timing flaw exists between the kernel IPsec driver and the SP5 cryptographic ring buffer. When a Phase 2 Security Association (SA) undergoes scheduled rekeying (typically every 28,800 seconds or 512 MB of transferred data), the SP5 hardware register fails to update the new 4-byte salt key negotiated during the quick mode exchange.

While outbound ESP payload encryption appears successful, the SP5 engine calculates an incorrect 16-byte Galois/Counter Mode Integrity Check Value (ICV) tag. The remote peer decrypts the packet, detects an ICV mismatch, and discards all incoming payload frames with ESP packet auth verification failed.

Affected Firmware & Blast Radius Matrix

Platform Impact: Confined specifically to FortiGate 90G and 91G hardware models equipped with the SP5 ASIC running AES-GCM-128 or AES-GCM-256 on route-based or policy-based IPsec VPN tunnels.

Step 01: Free Verification CLI (Safe Read-Only)

Execute these diagnostic commands to check SP5 hardware cryptographic stats and verify if IPsec tunnels are suffering from post-rekey auth tag drops:

# 1. Inspect SP5 hardware cryptographic engine counters and drop stats
diagnose npu sp5 ipsec-stats

# 2. Inspect active tunnel SA status and acceleration flags
diagnose vpn tunnel list | grep -E "name|npu_flag|spi"

# 3. Query active IKE Phase 1 security associations
diagnose vpn ike gateway list

# 4. Check real-time IPsec tunnel state
diagnose vpn ipsec status

Remediation & Workaround Steps (Teaser Preview)

Follow the complete step-by-step remediation guide in the Ferrite interactive platform:

Frequently Asked Questions