CVE-2026-2229

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

• CWE-248
• CWE-1284

• https://cna.openjsf.org/security-advisories.htmlVendor Advisory
• https://datatracker.ietf.org/doc/html/rfc7692Technical Description
• https://github.com/nodejs/undici/security/advisories/GHSA-v9p9-hfj2-hcw8Vendor Advisory
• https://hackerone.com/reports/3487486Permissions Required
• https://nodejs.org/api/zlib.html#class-zlibinflaterawTechnical Description

Published

Mar 12, 2026

Last Modified

Jun 17, 2026

Status

Analyzed