GitHub Advisoryadvisory · npm

GHSA-w293-vg96-wgc3 undici vulnerable to TLS certificate validation bypass via dropped connect options in BalancedPool

HIGH Published 2026-09-29 Modified 2026-09-29 Official page ↗
Aliases
CVE-2026-84961
Ecosystem
npm
Packages
undici
Severity
High
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Weaknesses
CWE-295
Reviewed
2026-09-29

Affected packages

• npm undici: >= 7.24.1, < 7.29.1 → fixed in 7.29.1 • npm undici: >= 8.0.0, < 8.10.2 → fixed in 8.10.2

Description

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.

Related

Alias · CVE (1)

  • CVE-2026-84961 undici's BalancedPool constructor passes its entire options object through an internal deep-clone that serializes and reparses the value as… vulnerability

Weakness · CWE (1)

  • CWE-295 Improper Certificate Validation weakness

References