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CVE-2026-21713

MEDIUMCVSS 5.9/10EPSS 0.39%

Last modified

CVE-2026-21713 is a medium-severity vulnerability rated 5.9/10 on the CVSS scale. 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**.. EPSS estimates a 0.39% chance of exploitation in the next 30 days.

Description

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**.

Metrics

CVSS 3.0
5.9/10

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS Probability
0.39%

31.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
NodejsNode.Js<= 20.20.1
NodejsNode.Js>= 22.0.0, <= 22.22.1
NodejsNode.Js>= 24.0.0, <= 24.14.0
NodejsNode.Js>= 25.0.0, <= 25.8.1

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-21713?
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**.
How severe is CVE-2026-21713?
CVE-2026-21713 has a CVSS score of 5.9/10 (MEDIUM severity). The EPSS model estimates a 0.39% probability of exploitation in the next 30 days.
How do I fix CVE-2026-21713?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST