FortiOS 7.0 to 7.2 Migration: Interface Alias Truncation & Orphaned Policy NAT
Upgrading firewalls from FortiOS 7.0 to early 7.2 releases silently clips interface alias strings longer than 25 characters in the intermediate migration parser, invalidating policy references and causing Policy NAT rules to orphan silently.
Technical Root Cause Analysis
In FortiOS 7.0, the schema under config system interface permitted administrator-assigned alias strings up to 63 characters via set alias <string>. During the automated configuration migration pipeline invoked when upgrading from FortiOS 7.0 to FortiOS 7.2.0–7.2.3, the intermediate schema parser function fcnfg_migrate_v70_to_v72 enforced a strict 25-character boundary limit.
When an interface alias exceeded 25 characters, the parser truncated the string without updating dependent configuration nodes. Subsequent compilation passes for config firewall policy, config firewall central-snat-map, and interface zones failed to match the truncated string against existing policy references. Consequently, affected policies lost their egress interface associations, orphaning outbound SNAT pools and directing enterprise traffic into the implicit deny catch-all.
Affected Firmware & Blast Radius Matrix
| FortiOS Branch | Vulnerable Builds | Confirmed Clean Build | Status & Workaround |
|---|---|---|---|
| FortiOS 7.2 | 7.2.0 – 7.2.3 | 7.2.4+ | Shorten aliases <25 chars before upgrade |
| FortiOS 7.0 | Not Affected | 7.0.x Branch Clean | Source branch supports 63-char strings |
| FortiOS 7.4 | Not Affected | 7.4.0+ | Direct 7.0 to 7.4 migration paths enforce clean schema |
Platform Impact: Affects all FortiGate hardware models (FG-40F through FG-3600E) and VM platforms migrating configuration files from FortiOS 7.0 to 7.2.0–7.2.3 with long descriptive interface naming schemes.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these diagnostic commands to inspect the post-upgrade configuration checksums and identify any truncated interface aliases or failed policy compilation lines:
Diagnostic Commands
# 1. Verify system configuration checksum and detect fgt compilation errors
diagnose sys checkum fgt
# 2. Inspect active interface aliases and identify clipped descriptions
show system interface | grep -A 3 -B 1 "alias"
# 3. Read boot-time configuration parsing errors for unresolvable references
diagnose debug config-error-log readRemediation & Workaround Steps (Teaser Preview)
Follow the complete step-by-step remediation guide in the Ferrite interactive platform:
Frequently Asked Questions
When the interface alias truncated during config parsing, rules binding that alias failed schema validation and were discarded from active runtime memory, leaving traffic to hit fallback policies.
Yes. You can either manually update the interface alias strings to 25 characters or fewer and rebind the policies, or upgrade directly to FortiOS 7.2.4+ which restores full 63-character alias parsing.
Physical interface names (e.g., port1, vlan100) are unaffected. The truncation strictly targets the set alias string metadata parsed under config system interface.