---
title: "CVE-2026-44351: fast-jwt: JWT auth bypass due to empty HMAC secret accepted by async key resolver"
url: https://erroneo.us/security/cve/CVE-2026-44351/
description: "CVE-2026-44351 (fast-jwt (npm)): fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.4, a critical authentication-bypass vulnerability…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-13
date_modified: 2026-05-14
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-44351"
kev: false
cvss: 9.1
epss: 0.00334
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-44351: fast-jwt: JWT auth bypass due to empty HMAC secret accepted by async key resolver

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.3% , percentile 25: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 25% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes fast-jwt (npm) <= 6.2.3, fixed in 6.2.4 . Check your lockfile, including transitive dependencies.

## What it is

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.2.4, a critical authentication-bypass vulnerability in fast-jwt's async key-resolver flow allows any unauthenticated attacker to forge arbitrary JWTs that are accepted as authentic. When the application's key resolver returns an empty string (''), for example via the common keys[decoded.header.kid] || '' JWKS-style fallback, fast-jwt converts it to a zero-length Buffer, hands it to crypto.createSecretKey, derives allowedAlgorithms = ['HS256','HS384','HS512'] from it, and then verifies the token's signature against an empty-key HMAC. The attacker simply computes HMAC-SHA256(key='', input='${header}.${payload}'), which Node accepts without complaint — and the verifier returns the attacker-chosen payload (sub, admin, scopes, etc.) as authentic. This vulnerability is fixed in 6.2.4.

## Affected packages

- npm `fast-jwt` <= 6.2.3 → fixed: 6.2.4

## Affected products (CVE record)

- nearform fast-jwt: < 6.2.4

## Severity

- GitHub_M CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`
- GitHub CVSS 3.1: 9.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.33% probability of exploitation activity in the next 30 days; percentile 25.

## Sources

- [GitHub Advisory GHSA-gmvf-9v4p-v8jc](https://github.com/advisories/GHSA-gmvf-9v4p-v8jc)
- [CVE.org record CVE-2026-44351](https://www.cve.org/CVERecord?id=CVE-2026-44351)
- [NVD entry CVE-2026-44351](https://nvd.nist.gov/vuln/detail/CVE-2026-44351)
- [github.com](https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc)

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Source page: https://erroneo.us/security/cve/CVE-2026-44351/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt