Outage in Firebase
Firebase Hosting and App Hosting returning unexpected 431 errors on some POST requests
Resolved Minor
January 06, 2026 - Started 5 days ago
- Lasted about 1 hour
Incident Report
POST requests against Firebase Hosting Sites with rewrites to Cloud Run or Firebase Fuctions and App Hosting Backends can occasionally return unexpected 431 errors. The issue is related to necessary networking headers the products add before routing requests to Cloud Run and Firebase Functions, and only occurs if the receiving Service/Function has strictly enforced header size limits. To mitigate, increase header size limits by at least 42 bytes.
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