Cloudflare blames today's outage on React2Shell mitigations

Earlier today, Cloudflare experienced a widespread outage that caused websites and online platforms worldwide to go down, returning a "500 Internal Server Error" message. The internet infrastructure company has now blamed the incident on the rollout of emergency mitigations designed to address a critical remote code execution vulnerability in React Server Components, which is now actively exploited in attacks. "The issue was not caused, directly or indirectly, by a cyber attack on Cloudflare’s systems or malicious activity of any kind. Instead, it was triggered by changes being made to our body parsing logic while attempting to detect and mitigate an industry-wide vulnerability disclosed this week in React Server Components," Cloudflare CTO Dane Knecht noted in a post-mortem. "A subset of customers were impacted, accounting for approximately 28% of all HTTP traffic served by Cloudflare." Tracked as CVE-2025-55182, this maximum severity security flaw (dubbed React2Shell) affects the React open-source JavaScript library for web and native user interfaces, as well as dependent React frameworks such as Next.js, React Router, Waku, @parcel/rsc, @vitejs/plugin-rsc, and RedwoodSDK. The vulnerability was found in the React Server Components (RSC) 'Flight' protocol, and it allows unauthenticated attackers to gain remote code execution in React and Next.js applications by sending maliciously crafted HTTP requests to React Server Function endpoints. While multiple React packages in the...