Cloudflare Outage: Technical Root Cause Revealed

Cloudflare experienced a 25-minute service disruption on December 5, 2025, affecting 28% of HTTP traffic due to a configuration change in its Web Application Firewall (WAF) while mitigating a React Server Components vulnerability (CVE-2025-55182). The incident was triggered by a Lua code error in FL1 proxy when disabling an internal tool, causing HTTP 500 errors. Cloudflare confirmed no cyber attack was involved and detailed the technical flaw—attempting to index a nil value in ruleset logic. The post-mortem highlights lessons from a similar November 18 outage, outlining resilience improvements like enhanced rollouts, versioning, and ‘fail-open’ error handling. This analysis offers deep insights into cloud infrastructure reliability, security best practices, and the risks of rapid configuration changes, making it valuable for professionals in network security and DevOps.