Incomplete fix for CVE-2026-21637: loadSNI() in _tls_wrap.js lacks try/catch leading to Remote DoS

Exploitation

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

CVSS

not scored

EPSS

• CVE-2026-21637: 1.12% estimated exploitation activity in the next 30 days; percentile 66.19 (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.

A flaw in Node.js TLS error handling leaves `SNICallback` invocations unprotected against synchronous exceptions, while the equivalent ALPN and PSK callbacks were already addressed in CVE-2026-21637. This represents an incomplete fix of that prior vulnerability. When an `SNICallback` throws synchronously on unexpected input the exception bypasses TLS error handlers and propagates as an uncaught exception, crashing the Node.js process. * This vulnerability affects all Node.js versions that received the CVE-2026-21637 fix, including 20.x, 22.x, 24.x, and 25.x, on any TLS server where `SNICallback` may throw on unexpected `servername` input.

Published by the source

24 Mar 2026, 00:00 UTC

Last modified by the source

24 Mar 2026, 00:00 UTC

Source last checked

26 Oct 2026, 16:40 UTC

1. Revision 2 · published · 26 Oct 2026

   Published from vendor_advisory record nodejs-security-wg:core:163

2. Revision 1 · created · 26 Oct 2026

   Created from vendor_advisory record nodejs-security-wg:core:163

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# Patch Next advisory brief: CVE-2026-21637

Advisory: Incomplete fix for CVE-2026-21637: loadSNI() in _tls_wrap.js lacks try/catch leading to Remote DoS
IDs: CVE-2026-21637
Record: https://patchnext.com/advisories/cve-2026-21637 (revision 2, source checked 26 Oct 2026, 16:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Unrated
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: node 25.8.2, 24.14.1, 22.22.2, 20.20.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- runtime node: affected >= 20.0.0, < 20.20.2; >= 22.0.0, < 22.22.2; >= 24.0.0, < 24.14.1; >= 25.0.0, < 25.8.2; fixed in 24.14.1, 20.20.2, 25.8.2, 22.22.2

## Suggested inspection (read-only)
- runtime node: check the installed version with your package manager.

## 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 node.
- 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://raw.githubusercontent.com/nodejs/security-wg/main/vuln/core/163.json (Node.js security working group core entry 163 lists CVE-2026-21637 affecting node >=20.0.0 =22.0.0 =24.0.0 =25.0.0 <25.8.2)
- Verified: https://nodejs.org/dist/index.json (The nodejs.org release index dates the first patched release for CVE-2026-21637 to 2026-03-24.)

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