HMAC disclosure via non-constant-time signature comparison
Published Mar 30, 2026 · Updated Mar 30, 2026
Observable timing discrepancy in Node.js 20.x, 22.x, 24.x, and 25.x allows remote attackers to infer HMAC values via timing measurements. The HMAC verification path in crypto_hmac.cc calls memcmp() on user-provided signatures, so comparison time varies with the number of matching bytes. Exploitation requires an application to verify attacker-controlled signatures and repeated, high-resolution timing measurements; successful inference discloses an HMAC value.
Summary
What happened
Observable timing discrepancy in Node.js 20.x, 22.x, 24.x, and 25.x allows remote attackers to infer HMAC values via timing measurements. The HMAC verification path in crypto_hmac.cc calls memcmp() on user-provided signatures, so comparison time varies with the number of matching bytes. Exploitation requires an application to verify attacker-controlled signatures and repeated, high-resolution timing measurements; successful inference discloses an HMAC value.
The record
- CVE
- CVE-2026-21713
- Published
- Mar 30, 2026
- Updated
- Mar 30, 2026
- Vendor
- Node.js
- Product
- Node.js
- Classifications
- CWE-208
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 30, 2026CVE publishedPublication date reported by the CVE source.
- Mar 30, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0 <10.*
- Affected versionversion=11.0 <11.*
- Affected versionversion=12.0 <12.*
- Affected versionversion=13.0 <13.*
- Affected versionversion=14.0 <14.*
- Affected versionversion=15.0 <15.*
- Affected versionversion=16.0 <16.*
- Affected versionversion=17.0 <17.*
- Affected versionversion=18.0 <18.*
- Affected versionversion=19.0 <19.*
- Affected versionversion=20.20.1 <=20.20.1
- Affected versionversion=22.22.1 <=22.22.1
- Affected versionversion=24.14.0 <=24.14.0
- Affected versionversion=25.8.1 <=25.8.1
- Affected versionversion=4.0 <4.*
- Affected versionversion=5.0 <5.*
- Affected versionversion=6.0 <6.*
- Affected versionversion=7.0 <7.*
- Affected versionversion=8.0 <8.*
- Affected versionversion=9.0 <9.*
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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