CVE-2026-2229: Node.js Undici

High severity, CVSS 7.5. EPSS: 0.9% chance of exploitation in the next 30 days.

ImpactThe undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation of the server_max_window_bits parameter in the permessage-deflate extension. When a WebSocket client connects to a server, it automatically advertises support for permessage-deflate compression. A malicious server can respond with an out-of-range server_max_window_bits value (outside zlib's valid range of 8-15). When the server subsequently sends a compressed frame, the client attempts to create a zlib InflateRaw instance with the invalid windowBits value, causing a synchronous RangeError exception that is not caught, resulting in immediate process termination. The vulnerability exists because: * The isValidClientWindowBits() function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15 * The createInflateRaw() call is not wrapped in a try-catch block * The resulting exception propagates up through the call stack and crashes the Node.js process

Affected products

• Node.js Undici: before 6.24.0 (fixed in 6.24.0); from 7.0.0, before 7.24.0 (fixed in 7.24.0)

Published 2026-03-12. Last modified 2026-09-04.