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High, CVSS 7.5amended

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

CVE-2026-2229GHSA-v9p9-hfj2-hcw8

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (undici 7.24.0, 6.24.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm undici

    Affected
    < 6.24.0>= 7.0.0, < 7.24.0
    Fixed in
    6.24.0, 7.24.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2026-2229: 0.91% estimated exploitation activity in the next 30 days; percentile 60.01 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact The undici WebSocket client is vulnerable to a denial-of-service attack due to improper validation of the servermaxwindowbits 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 servermaxwindowbits 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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-v9p9-hfj2-hcw8

  2. Revision 1 · created ·

    Published from osv record GHSA-v9p9-hfj2-hcw8

Agent brief

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# Patch Next advisory brief: CVE-2026-2229

Advisory: Undici has Unhandled Exception in WebSocket Client Due to Invalid server_max_window_bits Validation
IDs: CVE-2026-2229, GHSA-v9p9-hfj2-hcw8
Record: https://patchnext.com/advisories/cve-2026-2229 (revision 2, source checked 26 Oct 2026, 12:46 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: undici 7.24.0, 6.24.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm undici: affected < 6.24.0; >= 7.0.0, < 7.24.0; fixed in 6.24.0, 7.24.0

## Suggested inspection (read-only)
- `npm ls undici --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on undici.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-v9p9-hfj2-hcw8 (OSV record GHSA-v9p9-hfj2-hcw8 lists affected ranges: npm undici >=0 =7.0.0 <7.24.0 (fixed))
- Verified: https://github.com/advisories/GHSA-v9p9-hfj2-hcw8 (GitHub-reviewed advisory GHSA-v9p9-hfj2-hcw8 lists affected ranges: npm undici >=0 =7.0.0 <7.24.0)

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