Known Issue: FME Flow 2026.3.x and backported versions fail to re-register FME Engines after an invalid JSON security override is applied

Issue

In FME Flow 2026.2 and specified versions containing backported security updates, saving invalid JSON as a security override may throw an error that prevents engines from registering: 

Cause

Malformed JSON is not validated prior to being saved, so a syntax error in the override is only caught at startup.

This applies to the updated versions and instances that have been patched according to the instructions in the advisory: 

• 2026.3, 2026.3.1
• 2026.2, 2026.2.1
• 2026.1.2.1
• 2025.2.4.2
• 2025.1.3.5
• 2025.0.3.2
• 2024.2.5.2
• FME Flow instances with the hotfix patch and upgraded engine installed per the resolution option for backported security fixes described in the FME November 2026 Security Updates:
  • 2026.1.0.0 through 2026.1.2.0
  • 2025.2.0.0 through 2025.2.4.1
  • 2025.1.0.0 through 2025.1.3.4
  • 2025.0.0.0 through 2025.0.3.1
  • 2024.2.0.0 through 2024.2.5.1

Workaround

Edit the Override from the Security Hardening configuration in the Flow Web UI

Navigate to System Configuration > Security > Security Hardening in the Flow Web UI and edit the Configuration JSON to contain a valid security override JSON object, or disable the Custom Security Override if no security override is necessary

Earlier Versions: Edit engineconfig_patch.json file

Navigate to <FME_HOME>/res/engineconfig_patch.json and edit the file to contain a valid security override JSON object, or delete it if no security override is necessary. For assistance with applying overrides, please contact Support.

Related Issues

Known Issue: FME Form 2026.2 and backported versions fail to open after an invalid JSON security override is applied