CVE-2026-84961: Undici Undici Vulnerable To TLS Certificate Vulnerability

HIGH
Advisory Identifier: GHSA-w293-vg96-wgc3
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CVSS 7.4
CWE-295
Published
Advisory Summary

CVE-2026-84961 is a HIGH (CVSS 7.4) undici vulnerable to tls certificate vulnerability (CWE-295: Improper Certificate Validation) affecting Undici libraries in the npm ecosystem. The issue involves undici vulnerable to tls certificate validation bypass via dropped connect options in balancedpool. Remediation is available by upgrading affected packages to version 7.29.1, 8.10.2.

CVE-2026-84961 at a Glance

CVE Identifier CVE-2026-84961
GHSA Identifier GHSA-w293-vg96-wgc3
Severity HIGH
CVSS v3.1 Base Score 7.4
CWE Classification CWE-295: Improper Certificate Validation
Affected Product Undici
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 7.4

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

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

How to Fix CVE-2026-84961

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: 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-2026-84961, 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 7.29.1), 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-295: Improper Certificate Validation, where the product does not validate, or incorrectly validates, a certificate. 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 undici's `BalancedPool` passes its constructor options through a JSON-based deep clone (`JSON.parse(JSON.stringify(...))`) before forwarding them to each per-upstream `Pool`. JSON cannot represent functions, so a caller-supplied `connect` or `tls` option containing a `checkServerIdentity` callback (or a custom connector function) is silently dropped before it reaches the TLS layer. As a result, a TLS peer whose certificate a custom `checkServerIdentity` was written to reject, but which passes Node's default hostname and chain checks, is silently accepted when the request is made through `BalancedPool`. `Client`, `Pool`, `Agent`, and `RoundRobinPool` destructure `connect`/`tls` before the clone and are not affected. Only applications that use `BalancedPool` with a function-valued `connect`/`tls` option (such as a custom `checkServerIdentity` or connector) are affected. ### Patches Upgrade to `7.29.1` or `8.10.2`. `BalancedPool` now preserves the `connect` and `tls` options outside the JSON clone, so custom TLS verification callbacks are forwarded to each upstream unchanged. ### Workarounds Use `Client`, `Pool`, or `Agent` instead of `BalancedPool` for connections that rely on a custom `checkServerIdentity` or connector, until upgraded.

CVE-2026-84961 Affected Undici Versions

2 component(s)
Fixed Versions:
7.29.18.10.2
Product / Package Ecosystem Affected Versions Fixed Version
undici
npm/undici
npm
≥ 7.24.1
< 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-w293-vg96-wgc3
NVD — CVE-2026-84961 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-84961
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/8f5868fbdbc8f1146dfc1bcd1f2d117790141390
Security Fix Commit FIX COMMIT
https://github.com/nodejs/undici/commit/f690157d728508652fef14673630c71515123e96
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/v7.29.1
Undici Release RELEASE
https://github.com/nodejs/undici/releases/tag/v8.10.2

Frequently Asked Questions

What is CVE-2026-84961?
CVE-2026-84961 is a security vulnerability in Undici involving undici vulnerable to TLS certificate validation bypass via dropped connect options in BalancedPool under CWE-295: Improper Certificate Validation.
Which Undici versions are affected?
Affected versions include releases prior to 7.29.1, 8.10.2 across affected packages: undici.
What version fixes CVE-2026-84961?
Upgrading to 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 7.29.1, 8.10.2. Upgrade your dependency to 7.29.1, 8.10.2 or later.
What is the CVSS score of CVE-2026-84961?
CVE-2026-84961 has a CVSS v3.1 base score of 7.4 (HIGH) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N.
What CWE is associated with CVE-2026-84961?
CVE-2026-84961 is classified under CWE-295: Improper Certificate Validation (The product does not validate, or incorrectly validates, a certificate.).
How can I check npm dependencies for CVE-2026-84961?
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-w293-vg96-wgc3",
  "modified" : "2026-09-29T18:17:15Z",
  "published" : "2026-09-29T18:17:15Z",
  "aliases" : [ "CVE-2026-84961" ],
  "summary" : "undici vulnerable to TLS certificate validation bypass via dropped connect options in BalancedPool",
  "details" : "### Impact\n\nundici's `BalancedPool` passes its constructor options through a JSON-based deep clone (`JSON.parse(JSON.stringify(...))`) before forwarding them to each per-upstream `Pool`. JSON cannot represent functions, so a caller-supplied `connect` or `tls` option containing a `checkServerIdentity` callback (or a custom connector function) is silently dropped before it reaches the TLS layer. As a result, a TLS peer whose certificate a custom `checkServerIdentity` was written to reject, but which passes Node's default hostname and chain checks, is silently accepted when the request is made through `BalancedPool`. `Client`, `Pool`, `Agent`, and `RoundRobinPool` destructure `connect`/`tls` before the clone and are not affected. Only applications that use `BalancedPool` with a function-valued `connect`/`tls` option (such as a custom `checkServerIdentity` or connector) are affected.\n\n### Patches\n\nUpgrade to `7.29.1` or `8.10.2`. `BalancedPool` now preserves the `connect` and `tls` options outside the JSON clone, so custom TLS verification callbacks are forwarded to each upstream unchanged.\n\n### Workarounds\n\nUse `Client`, `Pool`, or `Agent` instead of `BalancedPool` for connections that rely on a custom `checkServerIdentity` or connector, until upgraded.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "undici"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "7.24.1"
      }, {
        "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-w293-vg96-wgc3"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84961"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/8f5868fbdbc8f1146dfc1bcd1f2d117790141390"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/commit/f690157d728508652fef14673630c71515123e96"
  }, {
    "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/v7.29.1"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nodejs/undici/releases/tag/v8.10.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-295" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-29T18:17:15Z",
    "nvd_published_at" : "2026-09-04T17:17:02Z"
  }
}