CVE-2026-23869 is a denial of service vulnerability in React Server Components, caused by improper handling of cyclic data structures during deserialization of incoming HTTP requests. The vulnerability resides in the React Flight protocol's server-side reply handling, specifically in the createMap, createSet, and extractIterator functions within ReactFlightReplyServer.js. The vulnerability carries a CVSS v3.1 base score of 7.5 (High). Exploitation requires no authentication and no user interaction.