CVE-2026-44351: nearform fast-jwt authentication bypass in async key resolver

CVE-2026-44351 · Severity: critical · CVSS 9.1 · Published 2026-05-13

A security flaw in the fast-jwt library allows attackers to bypass authentication and gain unauthorized access to applications. By providing a specially crafted token signed with an empty key, an attacker can impersonate any user, including administrators, if the application's key lookup fails or returns an empty value. This could lead to full account takeover and unauthorized access to sensitive customer data.

Technologies: fast-jwt (npm). Vendors: npm.

Quick answers

Is CVE-2026-44351 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-44351 being exploited in the wild.
How severe is CVE-2026-44351?
Critical severity, with a CVSS score of 9.1, published 13 May 2026.
Which products and versions are affected?
fast-jwt (npm) <= 6.2.3, SEMVER:introduced=0,fixed=6.2.4.
Is there a fix for CVE-2026-44351?
Yes. fast-jwt (npm): upgrade to 6.2.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-44351 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-44351?
Check whether you run fast-jwt (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • fast-jwt (npm): upgrade to 6.2.4 or later
    npm install fast-jwt@6.2.4

Technical details

The vulnerability exists in the asynchronous key-resolver flow within `src/verifier.js`. When a developer-provided `key` callback returns an empty string (`''`) or a zero-length Buffer, the library fails to validate the key length and defaults to HMAC algorithms (HS256, HS384, HS512). An attacker can then sign a JWT using an empty HMAC secret, which the library accepts as valid. This occurs because `prepareKeyOrSecret` does not perform a length check on the derived secret before passing it to Node's `crypto.createSecretKey`. The issue is specifically present in the async path; the synchronous path correctly rejects falsy keys. A patch is available in version 6.2.4.

Affected products

  • nearform fast-jwt <= 6.2.3

Identifiers

  • CVE-2026-44351
  • GHSA-gmvf-9v4p-v8jc

Timeline

  • 2026-04-29: disclosed
  • 2026-05-06: advisory: GHSA-gmvf-9v4p-v8jc published
  • 2026-05-14: other: Advisory updated

References

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