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.
Does this matter?
Lower severity and a low EPSS score (0.39%). Track it; it rarely justifies an emergency change on its own.
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**.
- CVSS 3.0
- 5.9 MEDIUMCVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- EPSS
- 0.39% probability · 32th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-208
- Affected
- nodejs/node.js
- Source
- support@hackerone.com
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.