CVE-2026-2229: Undici Undici Has Unhandled Exception Vulnerability

HIGH
Advisory Identifier: GHSA-v9p9-hfj2-hcw8
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CVSS 7.5
CWE-248
Published
Advisory Summary

CVE-2026-2229 is a HIGH (CVSS 7.5) undici has unhandled exception vulnerability (CWE-248: Uncaught Exception) affecting Undici libraries in the npm ecosystem. The issue involves undici has unhandled exception in websocket client due to invalid server_max_window_bits validation. Remediation is available by upgrading affected packages to version 6.24.0, 7.24.0.

CVE-2026-2229 at a Glance

CVE Identifier CVE-2026-2229
GHSA Identifier GHSA-v9p9-hfj2-hcw8
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-248: Uncaught Exception
Affected Product Undici
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability High (A:H)

How to Fix CVE-2026-2229

To remediate this vulnerability, upgrade all affected Undici dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

undici fixed: 6.24.0 
npm install undici@6.24.0
undici fixed: 7.24.0 
npm install undici@7.24.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls undici

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-2229, inspect your project dependencies using npm:

npm ls undici

Analyze the terminal output to locate any version of Undici in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.24.0), your application is affected.

Note: The npm ls undici command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-248: Uncaught Exception, where an exception is thrown from a function, but it is not caught. In Undici, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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?_

CVE-2026-2229 Affected Undici Versions

2 component(s)
Fixed Versions:
6.24.07.24.0
Product / Package Ecosystem Affected Versions Fixed Version
undici
npm/undici
npm
< 6.24.0
6.24.0
undici
npm/undici
npm
≥ 7.0.0
< 7.24.0
7.24.0

References

Undici Source Repository REPOSITORY
https://github.com/nodejs/undici
GitHub Advisory / Wiki ADVISORY
https://github.com/nodejs/undici/security/advisories/GHSA-v9p9-hfj2-hcw8
NVD — CVE-2026-2229 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-2229
hackerone.com/reports/3487486 WEB
https://hackerone.com/reports/3487486
Undici Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
datatracker.ietf.org/doc/html/rfc7692 WEB
https://datatracker.ietf.org/doc/html/rfc7692
nodejs.org/api/zlib.html WEB
https://nodejs.org/api/zlib.html#class-zlibinflateraw

Frequently Asked Questions

What is CVE-2026-2229?
CVE-2026-2229 is a security vulnerability in Undici involving Undici has Unhandled Exception in WebSocket Client Due to Invalid server_max_window_bits Validation under CWE-248: Uncaught Exception.
Which Undici versions are affected?
Affected versions include releases prior to 6.24.0, 7.24.0 across affected packages: undici.
What version fixes CVE-2026-2229?
Upgrading to 6.24.0, 7.24.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is undici affected?
Yes, undici is affected in releases prior to 6.24.0, 7.24.0. Upgrade your dependency to 6.24.0, 7.24.0 or later.
What is the CVSS score of CVE-2026-2229?
CVE-2026-2229 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
What CWE is associated with CVE-2026-2229?
CVE-2026-2229 is classified under CWE-248: Uncaught Exception (An exception is thrown from a function, but it is not caught.).
How can I check npm dependencies for CVE-2026-2229?
Run the dependency tree command: 'npm ls undici'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-v9p9-hfj2-hcw8",
  "modified" : "2026-03-13T20:41:41Z",
  "published" : "2026-03-13T20:41:41Z",
  "aliases" : [ "CVE-2026-2229" ],
  "summary" : "Undici has Unhandled Exception in WebSocket Client Due to Invalid server_max_window_bits Validation",
  "details" : "### Impact\n\nThe 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.\n\nThe vulnerability exists because:\n\n1. The `isValidClientWindowBits()` function only validates that the value contains ASCII digits, not that it falls within the valid range 8-15\n2. The `createInflateRaw()` call is not wrapped in a try-catch block\n3. The resulting exception propagates up through the call stack and crashes the Node.js process\n\n### Patches\n_Has the problem been patched? What versions should users upgrade to?_\n\n### Workarounds\n_Is there a way for users to fix or remediate the vulnerability without upgrading?_",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
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      }, {
        "fixed" : "6.24.0"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
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      "type" : "ECOSYSTEM",
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      }, {
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      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
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  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-2229"
  }, {
    "type" : "WEB",
    "url" : "https://hackerone.com/reports/3487486"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "WEB",
    "url" : "https://datatracker.ietf.org/doc/html/rfc7692"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nodejs/undici"
  }, {
    "type" : "WEB",
    "url" : "https://nodejs.org/api/zlib.html#class-zlibinflateraw"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-248" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-13T20:41:41Z",
    "nvd_published_at" : "2026-03-12T21:16:25Z"
  }
}