FortiOS 7.4.3 Web GUI Blank White Screen Bug due to Asset Cache Hash Mismatch
Following firmware upgrade to FortiOS 7.4.3, administrators accessing the web management portal encounter an unresponsive blank white screen caused by Webpack JavaScript chunk hash mismatches and stale browser asset caching.
Technical Root Cause Analysis
The FortiOS administrative interface is constructed as a modern Single Page Application (SPA) compiled into code-split Webpack JavaScript chunks.
In FortiOS 7.4.3 Build 2480, several underlying vendor chunks were recompiled, altering their content hashes. However, the static asset manifest served by the internal web daemon (/bin/httpsd) failed to enforce appropriate cache-invalidation headers (must-revalidate).
When administrators access the management IP using an existing browser session, the browser attempts to execute the cached bootstrap script containing stale chunk references. As the client requests obsolete chunk filenames from httpsd, the server responds with HTTP 404 Not Found, throwing an unhandled ChunkLoadError in the browser runtime and halting UI rendering before the login portal or dashboard can mount.
Affected Firmware & Blast Radius Matrix
| FortiOS Branch | Vulnerable Builds | Confirmed Clean Build | Status & Workaround |
|---|---|---|---|
| FortiOS 7.4 | 7.4.3 (Build 2480) | 7.4.4+ | Hard refresh (Ctrl+F5) or Incognito window |
| FortiOS 7.2 | Not Affected | 7.2.x Branch Clean | Legacy chunk loader uses version-pinned query strings |
| FortiOS 7.0 | Not Affected | 7.0.x Branch Clean | Different frontend UI bundle architecture |
Platform Impact: Affects all FortiGate hardware appliances and virtual machines running FortiOS 7.4.3 Build 2480 when managed via Chrome, Edge, Safari, or Firefox browsers with existing cached assets.
Step 01: Free Verification CLI (Safe Read-Only)
Execute these diagnostic commands to verify httpsd process health and confirm the exact FortiOS firmware build number:
Diagnostic Commands
# 1. Verify that httpsd web server processes are running normally
diagnose sys process pidof httpsd
# 2. Confirm exact FortiOS firmware build and branch
get system status | grep -E "Version|Branch"
# 3. Check management CPU utilization
diagnose sys top-summary "sort=cpu"
# 4. In browser: Press F12 -> Console tab -> Check for "ChunkLoadError"Remediation & Workaround Steps (Teaser Preview)
Follow the complete step-by-step remediation guide in the Ferrite interactive platform:
Frequently Asked Questions
Administrators who access the FortiGate with a fresh browser or in Incognito mode download the new 7.4.3 assets cleanly. Those with pre-existing browser cache files from 7.4.2 or 7.2.x hit the chunk hash mismatch.
No. Executing fnsysctl killall httpsd restarts only the administrative web GUI listener. Transit firewall traffic and IPsec tunnels forwarded in kernel space and hardware ASICs are completely uninterrupted.
Yes. CLI access over SSH and centralized management via FortiManager remain fully operational throughout the incident.