CVE-2026-2229 undici is vulnerable to Unhandled Exception in undici WebSocket Client Due to Invalid server_max_window_bits Validation
A malicious WebSocket server can crash a Node.js application by sending an invalid compression parameter, causing an unhandled exception.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-2229?
CVE-2026-2229 is a high-severity denial of service vulnerability in Nodejs Undici, published on 12 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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
Which versions are affected by CVE-2026-2229?
4 open source packages ship an affected version, including undici. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
undici npm | All versions | 6.24.0 |
undici npm | All versions | 6.24.0 |
undici npm | From 7.0.0 | 7.24.0 |
undici npm | From 7.0.0 | 7.24.0 |
Products include Nodejs Undici.
How do I fix CVE-2026-2229?
Upgrade undici to a fixed version for your release line: 6.24.0 or 7.24.0.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-2229 being exploited?
There is no known exploitation of CVE-2026-2229 in the wild and no public exploit code.
Other vulnerabilities in Nodejs Undici
- CVE-2026-109855 undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake
- CVE-2026-109869 undici vulnerable to Denial of Service via unhandled error on excessive content-encodings
- CVE-2026-87018 undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation
- CVE-2026-19534 undici vulnerable to Denial of Service via unrequested WebSocket subprotocol
- CVE-2026-12151 undici WebSocket client vulnerable to denial of service via fragment count bypass
Sources
Also known as BELL-CVE-2026-2229, CLEANSTART-2026-NW80609, CLEANSTART-2026-QF25668, CLSA-2026-1791192281, DEBIAN-CVE-2026-2229, ECHO-f0a7-0b20-68fa and 14 more.