---
id: CVE-2026-84961
title: >-
  undici's BalancedPool constructor passes its entire options object through an
  internal deep-clone that serializes and reparses the value as JSON
summary: >-
  undici's BalancedPool constructor passes its entire options object through an
  internal deep-clone that serializes and reparses the value as JSON. Because
  JSON cannot represent functions, any function-valued TLS option, such as a
  caller-s…
severity: high
cvss: 7.4
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N'
cwe:
  - CWE-295
vendor: nodejs
product: undici
affected:
  - 'undici >= 7.24.1, < 7.29.1'
  - 'undici >= 8.0.0, < 8.10.2'
patched:
  - undici 8.10.2
published: '2026-09-04'
updated: '2026-09-15'
sourceUpdated: '2026-09-15T14:29:35.253'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-84961'
references:
  - url: 'https://cna.openjsf.org/security-advisories.html'
    label: ce714d77-add3-4f53-aff5-83d477b104bb
  - url: 'https://github.com/nodejs/undici/security/advisories/GHSA-w293-vg96-wgc3'
    label: ce714d77-add3-4f53-aff5-83d477b104bb
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-84961.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-84961'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2528735'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-84961'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-84961'
  - url: 'https://access.redhat.com/errata/RHSA-2026:66008'
  - url: 'https://access.redhat.com/errata/RHSA-2026:66605'
  - url: 'https://access.redhat.com/errata/RHSA-2026:69248'
  - url: 'https://access.redhat.com/errata/RHSA-2026:54438'
tags:
  - nvd
  - csaf
  - vex
  - red-hat
epss: 0.00248
epssPercentile: 0.14329
ingestedAt: '2026-09-08T19:08:49.593Z'
---

## Overview

undici's BalancedPool constructor passes its entire options object through an internal deep-clone that serializes and reparses the value as JSON. Because JSON cannot represent functions, any function-valued TLS option, such as a caller-supplied checkServerIdentity callback or a custom connector inside the connect option, is silently discarded before it reaches the TLS layer. As a result a peer whose certificate the application's custom checkServerIdentity was written to reject, but which still passes Node's default hostname and chain checks, is accepted when reached through BalancedPool. The Client, Pool, and Agent dispatchers are not affected because they extract the connect and tls options before cloning. This affects undici versions from 7.24.1 up to 7.29.1 and from 8.0.0 up to 8.10.2, and only when the application supplies a function-valued connect or tls option to BalancedPool. Users should upgrade to undici 7.29.1 or 8.10.2.

## Affected

- `undici >= 7.24.1, < 7.29.1`
- `undici >= 8.0.0, < 8.10.2`

## Remediation

Upgrade past the affected range:

- `undici 8.10.2`

## Vendor advisories

- **Red Hat VEX** · Important · affected: Exploit Intelligence, OpenShift Pipelines, Red Hat Build of Podman Desktop, Red Hat Developer Hub, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, … · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat Hardened Images, … · updated 2026-09-23 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-84961.json)
- **RHSA-2026:66008** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-09 · [advisory](https://access.redhat.com/errata/RHSA-2026:66008)
- **RHSA-2026:66605** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-11 · [advisory](https://access.redhat.com/errata/RHSA-2026:66605)
- **RHSA-2026:69248** · Red Hat · fixed in: Red Hat Developer Hub 1.9 · released 2026-09-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:69248)
- **RHSA-2026:54438** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-12 · [advisory](https://access.redhat.com/errata/RHSA-2026:54438)