# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 12 Mar 2026
- **Updated:** 14 Sep 2026
- **Also known as:** BELL-CVE-2026-2229, CLEANSTART-2026-NW80609, CLEANSTART-2026-QF25668, CLSA-2026-1791192281, DEBIAN-CVE-2026-2229, ECHO-f0a7-0b20-68fa, GHSA-v9p9-hfj2-hcw8, MINI-5qf9-2p9g-xmq8, MINI-65xf-r9qr-9mq3, MINI-69fm-wpqw-w69r, MINI-96px-rgv6-ch9f, MINI-ccx2-3gfr-wwvj, MINI-jpgq-4g65-2j5p, MINI-pqj5-9pj5-qvxq, MINI-q66h-8gc6-r4gh, MINI-q8rj-9x4m-mm6v, MINI-x46j-95ch-4wwh, MINI-x867-8hp3-3h4j, ROOT-APP-NPM-CVE-2026-2229, UBUNTU-CVE-2026-2229

## 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

Weakness: CWE-248 (Uncaught Exception), CWE-1284 (Improper Validation of Specified Quantity in Input)

## Which versions are affected by CVE-2026-2229?

4 open source packages ship an affected version, including undici. It affects 1 product.


| Package | Ecosystem | 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: 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.

## 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](https://insights.sbomify.com/CVE-2026-109855/): undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake (high 7.5)
- [CVE-2026-109869](https://insights.sbomify.com/CVE-2026-109869/): undici vulnerable to Denial of Service via unhandled error on excessive content-encodings (high 7.5)
- [CVE-2026-87018](https://insights.sbomify.com/CVE-2026-87018/): undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation (high 7.5)
- [CVE-2026-19534](https://insights.sbomify.com/CVE-2026-19534/): undici vulnerable to Denial of Service via unrequested WebSocket subprotocol (high 7.5)
- [CVE-2026-12151](https://insights.sbomify.com/CVE-2026-12151/): undici WebSocket client vulnerable to denial of service via fragment count bypass (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-2229 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-2229 in the wild and no public exploit code.

Affected packages and fixed versions:
- undici (npm): affected all versions; fixed in 6.24.0
- undici (npm): affected all versions; fixed in 6.24.0
- undici (npm): affected from 7.0.0; fixed in 7.24.0
- undici (npm): affected from 7.0.0; fixed in 7.24.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-2229/ (Markdown: https://insights.sbomify.com/CVE-2026-2229/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2229
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2229
- OSV: https://osv.dev/vulnerability/CVE-2026-2229

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-2229/
Summaries are generated and may contain mistakes; the official description above is the record.