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CVE-2026-2229

Undici has Unhandled Exception in WebSocket Client Due to Invalid server_max_window_bits Validation

Impact

### Impact The 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: 1. The `isValidClientWindowBits()` function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15 2. The `createInflateRaw()` call is not wrapped in a try-catch block 3. The resulting exception propagates up through the call stack and crashes the Node.js process ### Patches _Has the problem been patched? What versions should users upgrade to?_ ### Workarounds _Is there a way for users to fix or remediate the vulnerability without upgrading?_

Affected packages

EcosystemPackageAffectedFixed in
npmundici< 6.24.06.24.0

Affected products

VendorProductAffected versions
NodejsUndici
before 6.24.0
from 7.0.0 before 7.24.0

Weakness classification

CWE-248CWE-1284

References