Medium · published March 31, 2026
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**.
| Product | Versions | Fixed in |
|---|---|---|
| nodejs/node.js | ≤ 20.20.1 | — |
| nodejs/node.js | ≥ 22.0.0, ≤ 22.22.1 | — |
| nodejs/node.js | ≥ 24.0.0, ≤ 24.14.0 | — |
| nodejs/node.js | ≥ 25.0.0, ≤ 25.8.1 | — |