MEDIUM 5.9 Microsoft

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**.

Microsoft Security Update 2026-Mar: 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**.

Affected Products

References

Published: 2026-03-10 · Source: Microsoft · Feed updated: 2026-08-10
This medium severity vulnerability with a CVSS score of 5.9 was published on 2026-03-10 via Microsoft. Affected: azl3 nodejs 20.14.0-14 on Azure Linux 3.0, azl3 nodejs24 24.13.0-3 on Azure Linux 3.0.
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