{"id":"CVE-2026-84961","aliases":["GHSA-w293-vg96-wgc3"],"url":"https://o3.security/vulnerability/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.","published":"2026-09-04T16:47:55.724Z","modified":"2026-10-21T02:30:38.730923979Z","cvss":{"score":7.4,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"undici","fixedVersion":"7.29.1"},{"ecosystem":"npm","name":"undici","fixedVersion":"8.10.2"}],"fix":{"url":"https://github.com/nodejs/undici/commit/8f5868fbdbc8f1146dfc1bcd1f2d117790141390","label":"nodejs/undici@8f5868f"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84961.json"},{"type":"ADVISORY","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":"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:30:38.730923979Z"}}