undici vulnerable to TLS certificate validation bypass via dropped tls options in Agent

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.4 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-109383: 0.18% estimated exploitation activity in the next 30 days; percentile 8.07 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact undici's `Agent` passes its constructor options through a JSON-based deep clone (`JSON.parse(JSON.stringify(...))`) before forwarding them to each per-origin `Pool`. JSON cannot represent functions, so a caller-supplied `tls` option containing a `checkServerIdentity` callback 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 `Agent`. Because `Agent` is the default dispatcher behind `request`, `fetch`, and `setGlobalDispatcher`, this is the path most applications use. `EnvHttpProxyAgent` is also affected on its direct and `NO_PROXY` routes, which delegate to an internal `Agent`. Only applications that pass a function-valued `tls` option (such as a custom `checkServerIdentity` for certificate or public-key pinning) are affected. Passing the same options through…

Published by the source

27 Oct 2026, 19:02 UTC

Last modified by the source

27 Oct 2026, 19:15 UTC

Source last checked

28 Oct 2026, 06:00 UTC

1. Revision 2 · amended · 28 Oct 2026

   Amended from osv record GHSA-2m5v-pch6-74hx

2. Revision 1 · created · 27 Oct 2026

   Published from ghsa record GHSA-2m5v-pch6-74hx

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# Patch Next advisory brief: CVE-2026-109383

Advisory: undici vulnerable to TLS certificate validation bypass via dropped tls options in Agent
IDs: CVE-2026-109383, GHSA-2m5v-pch6-74hx
Record: https://patchnext.com/advisories/cve-2026-109383 (revision 2, source checked 28 Oct 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: undici 8.12.2, 7.30.1, 6.29.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm undici: affected >= 4.0.0, < 6.29.1; >= 7.0.0, < 7.30.1; >= 8.0.0, < 8.12.2; fixed in 8.12.2, 6.29.1, 7.30.1

## Suggested inspection (read-only)
- `npm ls undici --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on undici.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-2m5v-pch6-74hx (GitHub-reviewed advisory GHSA-2m5v-pch6-74hx lists affected ranges: npm undici >=4.0.0 =7.0.0 =8.0.0 <8.12.2)
- Verified: https://osv.dev/vulnerability/GHSA-2m5v-pch6-74hx (OSV record GHSA-2m5v-pch6-74hx lists affected ranges: npm undici >=4.0.0 =7.0.0 =8.0.0 <8.12.2 (fixed))

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