Timing side-channel in HMAC verification via memcmp() in crypto_hmac.cc leads to potential MAC forgery

Exploitation

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

CVSS

not scored

EPSS

• CVE-2026-21713: 0.37% estimated exploitation activity in the next 30 days; percentile 30.56 (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 HMAC verification uses a non-constant-time comparison when validating user-provided signatures, potentially leaking timing information proportional to the number of matching bytes. Under certain threat models where high-resolution timing measurements are possible, this behavior could be exploited as a timing oracle to infer HMAC values. Node.js already provides timing-safe comparison primitives used elsewhere in the codebase, indicating this is an oversight rather than an intentional design decision. This vulnerability affects 20.x, 22.x, 24.x, and 25.x.

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:167

2. Revision 1 · created · 26 Oct 2026

   Created from vendor_advisory record nodejs-security-wg:core:167

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-21713

Advisory: Timing side-channel in HMAC verification via memcmp() in crypto_hmac.cc leads to potential MAC forgery
IDs: CVE-2026-21713
Record: https://patchnext.com/advisories/cve-2026-21713 (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://nodejs.org/dist/index.json (The nodejs.org release index dates the first patched release for CVE-2026-21713 to 2026-03-24.)
- Verified: https://raw.githubusercontent.com/nodejs/security-wg/main/vuln/core/167.json (Node.js security working group core entry 167 lists CVE-2026-21713 affecting node >=20.0.0 =22.0.0 =24.0.0 =25.0.0 <25.8.2)

Commands are suggestions: review each one before running it.