CVE-2026-19534: Undici Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-rfgv-xxqx-mfg5
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CVSS 7.5
CWE-252 CWE-248
Published
Advisory Summary

CVE-2026-19534 is a HIGH (CVSS 7.5) denial of service vulnerability (CWE-252: Unchecked Return Value) affecting Undici libraries in the npm ecosystem. The issue involves undici vulnerable to denial of service via unrequested websocket subprotocol. Remediation is available by upgrading affected packages to version 6.28.1, 7.29.1, 8.10.2.

CVE-2026-19534 at a Glance

CVE Identifier CVE-2026-19534
GHSA Identifier GHSA-rfgv-xxqx-mfg5
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-252: Unchecked Return Value
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-2026-19534

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: 6.28.1 
npm install undici@6.28.1
undici fixed: 7.29.1 
npm install undici@7.29.1
undici fixed: 8.10.2 
npm install undici@8.10.2
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-2026-19534, 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 6.28.1), 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-252: Unchecked Return Value, where the product does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions. 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 throws an uncaught `TypeError` during the opening handshake when a server's `101` response includes a `Sec-WebSocket-Protocol` header that the client never requested. The throw occurs in a `queueMicrotask` callback with no surrounding `try`/`catch`, so it propagates as an uncaught exception and terminates the Node.js process. This is a remote, unauthenticated denial of service against any application that opens a WebSocket to an attacker controlled or compromised server, or over a plaintext `ws://` connection subject to a machine-in-the-middle. It affects the default `new WebSocket(url)` usage, where no subprotocol is requested. Per RFC 6455 section 4.1, an unrequested subprotocol must fail the connection, not crash it. All releases starting at undici 6.7.0 are affected. ### Patches Upgrade to undici 6.28.1, 7.29.1, or 8.10.2. ### Workarounds No workaround is available. The fix must be applied through an upgrade.

CVE-2026-19534 Affected Undici Versions

3 component(s)
Fixed Versions:
6.28.17.29.18.10.2
Product / Package Ecosystem Affected Versions Fixed Version
undici
npm/undici
npm
≥ 6.7.0
< 6.28.1
6.28.1
undici
npm/undici
npm
≥ 7.0.0
< 7.29.1
7.29.1
undici
npm/undici
npm
≥ 8.0.0
< 8.10.2
8.10.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nodejs/undici/security/advisories/GHSA-rfgv-xxqx-mfg5
NVD — CVE-2026-19534 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-19534
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/2af0faf88b906d3127a360c3ac75164c0f95e5a5
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/6615e0175e9b635bcd2e3e87a47daa82f6f5b728
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/66e12816064cf3068f63bd134748b7fc4e779bad
Undici Security Information SECURITY
https://cna.openjsf.org/security-advisories.html
Undici Source Repository REPOSITORY
https://github.com/nodejs/undici
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v6.28.1
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v7.29.1
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v8.10.2

Frequently Asked Questions

What is CVE-2026-19534?
CVE-2026-19534 is a security vulnerability in Undici involving undici vulnerable to Denial of Service via unrequested WebSocket subprotocol under CWE-252: Unchecked Return Value.
Which Undici versions are affected?
Affected versions include releases prior to 6.28.1, 7.29.1, 8.10.2 across affected packages: undici.
What version fixes CVE-2026-19534?
Upgrading to 6.28.1, 7.29.1, 8.10.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is undici affected?
Yes, undici is affected in releases prior to 6.28.1, 7.29.1, 8.10.2. Upgrade your dependency to 6.28.1, 7.29.1, 8.10.2 or later.
What is the CVSS score of CVE-2026-19534?
CVE-2026-19534 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-2026-19534?
CVE-2026-19534 is classified under CWE-252: Unchecked Return Value (The product does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions.).
How can I check npm dependencies for CVE-2026-19534?
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-rfgv-xxqx-mfg5",
  "modified" : "2026-09-29T18:21:33Z",
  "published" : "2026-09-29T18:21:33Z",
  "aliases" : [ "CVE-2026-19534" ],
  "summary" : "undici vulnerable to Denial of Service via unrequested WebSocket subprotocol",
  "details" : "### Impact\n\nThe undici WebSocket client throws an uncaught `TypeError` during the opening handshake when a server's `101` response includes a `Sec-WebSocket-Protocol` header that the client never requested. The throw occurs in a `queueMicrotask` callback with no surrounding `try`/`catch`, so it propagates as an uncaught exception and terminates the Node.js process. This is a remote, unauthenticated denial of service against any application that opens a WebSocket to an attacker controlled or compromised server, or over a plaintext `ws://` connection subject to a machine-in-the-middle. It affects the default `new WebSocket(url)` usage, where no subprotocol is requested. Per RFC 6455 section 4.1, an unrequested subprotocol must fail the connection, not crash it.\n\nAll releases starting at undici 6.7.0 are affected.\n\n### Patches\n\nUpgrade to undici 6.28.1, 7.29.1, or 8.10.2.\n\n### Workarounds\n\nNo workaround is available. The fix must be applied through an upgrade.",
  "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" : [ {
        "introduced" : "6.7.0"
      }, {
        "fixed" : "6.28.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.0.0"
      }, {
        "fixed" : "7.29.1"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "8.0.0"
      }, {
        "fixed" : "8.10.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/security/advisories/GHSA-rfgv-xxqx-mfg5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-19534"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/2af0faf88b906d3127a360c3ac75164c0f95e5a5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/6615e0175e9b635bcd2e3e87a47daa82f6f5b728"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/66e12816064cf3068f63bd134748b7fc4e779bad"
  }, {
    "type" : "WEB",
    "url" : "https://cna.openjsf.org/security-advisories.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nodejs/undici"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v6.28.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v7.29.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v8.10.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-248", "CWE-252" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-29T18:21:33Z",
    "nvd_published_at" : "2026-09-04T18:17:51Z"
  }
}