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 zlibs 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

Weakness

An exception is thrown from a function, but it is not caught.

Affected Software

References

• https://cna.openjsf.org/security-advisories.html
• https://datatracker.ietf.org/doc/html/rfc7692
• https://github.com/nodejs/undici/security/advisories/GHSA-v9p9-hfj2-hcw8
• https://hackerone.com/reports/3487486
• https://nodejs.org/api/zlib.html#class-zlibinflateraw