Earlier immediately, Cloudflare skilled a widespread outage that precipitated web sites and on-line platforms worldwide to go down, returning a “500 Inner Server Error” message.
The web infrastructure firm has now blamed the incident on the rollout of emergency mitigations designed to deal with a essential distant code execution vulnerability in React Server Parts, which is now actively exploited in assaults.
“The difficulty was not precipitated, straight or not directly, by a cyber assault on Cloudflare’s programs or malicious exercise of any form. As a substitute, it was triggered by adjustments being made to our physique parsing logic whereas making an attempt to detect and mitigate an industry-wide vulnerability disclosed this week in React Server Parts,” Cloudflare CTO Dane Knecht famous in a autopsy.
“A subset of shoppers have been impacted, accounting for roughly 28% of all HTTP visitors served by Cloudflare.”
Tracked as CVE-2025-55182, this most severity safety flaw (dubbed React2Shell) impacts the React open-source JavaScript library for internet and native person interfaces, in addition to dependent React frameworks resembling Subsequent.js, React Router, Waku, @parcel/rsc, @vitejs/plugin-rsc, and RedwoodSDK.
The vulnerability was discovered within the React Server Parts (RSC) ‘Flight’ protocol, and it permits unauthenticated attackers to achieve distant code execution in React and Subsequent.js functions by sending maliciously crafted HTTP requests to React Server Perform endpoints.
Whereas a number of React packages of their default configuration (i.e., react-server-dom-parcel, react-server-dom-turbopack, and react-server-dom-webpack) are weak, the flaw solely impacts React variations 19.0, 19.1.0, 19.1.1, and 19.2.0 launched in the course of the previous 12 months.
Ongoing React2Shell exploitation
Though the affect will not be as widespread as initially believed, safety researchers with Amazon Net Companies (AWS) have reported that a number of China-linked hacking teams (together with Earth Lamia and Jackpot Panda) have begun exploiting the React2Shell vulnerability hours after the max-severity flaw was disclosed.
The NHS England Nationwide CSOC additionally mentioned on Thursday that a number of practical CVE-2025-55182 proof-of-concept exploits are already obtainable and warned that “continued profitable exploitation within the wild is extremely possible.”
Final month, Cloudflare skilled one other worldwide outage that introduced down the corporate’s World Community for nearly 6 hours, an incident described by CEO Matthew Prince because the “worst outage since 2019.”
Cloudflare mounted one other huge outage in June, which precipitated Entry authentication failures and Zero Belief WARP connectivity points throughout a number of areas, and likewise impacted Google Cloud’s infrastructure.
Replace December 05, 11:38 EST: Revised story and title primarily based on a autopsy shared by Cloudflare CTO Dane Knecht.
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