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undici vulnerable to TLS certificate validation bypass via dropped connect options in BalancedPool

Type: advisorySource: OSV1 source record

### 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.

Announced Group revision 1
Original source ↗

GHSA-w293-vg96-wgc3

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: osv:GHSA-w293-vg96-wgc3

undici

Source reference: /affected/0/package/name

Affected versions
Not stated in this record
Fixed versions
7.29.1

Source reference: /affected/0/ranges

Prerequisites
Not stated in this record

undici

Source reference: /affected/1/package/name

Affected versions
Not stated in this record
Fixed versions
8.10.2

Source reference: /affected/1/ranges

Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "ranges": [
      {
        "type": "SEMVER",
        "events": [
          {
            "introduced": "7.24.1"
          },
          {
            "fixed": "7.29.1"
          }
        ]
      }
    ],
    "package": {
      "name": "undici",
      "purl": "pkg:npm/undici",
      "ecosystem": "npm"
    },
    "database_specific": {
      "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-w293-vg96-wgc3/GHSA-w293-vg96-wgc3.json"
    }
  },
  {
    "ranges": [
      {
        "type": "SEMVER",
        "events": [
          {
            "introduced": "8.0.0"
          },
          {
            "fixed": "8.10.2"
          }
        ]
      }
    ],
    "package": {
      "name": "undici",
      "purl": "pkg:npm/undici",
      "ecosystem": "npm"
    },
    "database_specific": {
      "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-w293-vg96-wgc3/GHSA-w293-vg96-wgc3.json"
    }
  }
]
Related CVEs
CVE-2026-84961

Source reference: /aliases

Publisher severity

high

Source reference: /database_specific/severity

Event
#31145 · Revision 1
Added to Heist Feed
Publisher date
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