undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation

Exploitation

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

CVSS

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

EPSS

• CVE-2026-87018: 0.19% estimated exploitation activity in the next 30 days; percentile 8.41 (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 crashes the client process when a TLS 1.2 server renegotiates after the connection is established and presents a different, CA-trusted certificate whose hostname does not match the requested host. Node.js re-runs hostname verification on the renegotiated handshake and destroys the socket with `ERR_TLS_CERT_ALTNAME_INVALID`. undici's established socket error handler asserted that this error code could never occur, so the peer-controlled error became an uncaught `AssertionError` that terminates the Node.js process. Both the HTTP/1.1 and HTTP/2 paths are affected. A malicious or compromised HTTPS endpoint reached through undici or the global `fetch()` can crash the client with a single server-initiated renegotiation, taking down all in-flight requests and background work in the process. Only TLS 1.2 is affected, because TLS 1.3 does not support renegotiation. Exploitation does not require a CA compromise: the attacker controls the endpoint and can present two ordinary…

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-qrxm-fqhp-jwvm

2. Revision 1 · created · 27 Oct 2026

   Published from ghsa record GHSA-qrxm-fqhp-jwvm

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# Patch Next advisory brief: CVE-2026-87018

Advisory: undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation
IDs: CVE-2026-87018, GHSA-qrxm-fqhp-jwvm
Record: https://patchnext.com/advisories/cve-2026-87018 (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 7.5)
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 >= 4.2.1, < 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-qrxm-fqhp-jwvm (GitHub-reviewed advisory GHSA-qrxm-fqhp-jwvm lists affected ranges: npm undici >=4.2.1 =7.0.0 =8.0.0 <8.12.2)
- Verified: https://osv.dev/vulnerability/GHSA-qrxm-fqhp-jwvm (OSV record GHSA-qrxm-fqhp-jwvm lists affected ranges: npm undici >=4.2.1 =7.0.0 =8.0.0 <8.12.2 (fixed))

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