{"id":"GHSA-w293-vg96-wgc3","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.","aliases":["CVE-2026-84961"],"modified":"2026-09-29T18:28:14.915098573Z","published":"2026-09-29T18:17:15Z","database_specific":{"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-09-29T18:17:15Z","nvd_published_at":"2026-09-04T17:17:02Z","cwe_ids":["CWE-295"]},"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"}],"affected":[{"package":{"name":"undici","ecosystem":"npm","purl":"pkg:npm/undici"},"ranges":[{"type":"SEMVER","events":[{"introduced":"7.24.1"},{"fixed":"7.29.1"}]}],"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"}},{"package":{"name":"undici","ecosystem":"npm","purl":"pkg:npm/undici"},"ranges":[{"type":"SEMVER","events":[{"introduced":"8.0.0"},{"fixed":"8.10.2"}]}],"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"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"}]}