CVE-2026-44351 Details
Description
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.
A critical authentication-bypass vulnerability has been identified in fast-jwt versions through 6.2.3. This vulnerability allows unauthenticated attackers to forge JSON Web Tokens (JWTs) that are accepted as valid. The issue arises in the library's asynchronous key-resolver flow, where an empty string returned by the key resolver is converted into a zero-length Buffer. This empty key is then used to create a secret key for HMAC signing, allowing attackers to compute a valid signature for a forged token. The vulnerability is exploitable by anyone who can send a JWT to be verified, making it a serious security risk for applications using fast-jwt with a function-typed key resolver.
Users can upgrade to fast-jwt version 6.2.4, where this vulnerability has been fixed. The patch involves rejecting zero-length HMAC secrets in the key preparation function, preventing the authentication bypass.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed May 13, 2026CISA-ADP
Assessed May 14, 2026References to Advisories, Solutions, and Tools
By selecting these links, you will be leaving this site. These are references gathered from the official CVE record and are not endorsed by Volerion.
| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc | CISA-ADP | AdvisoryExploitRemedyVendor |
| https://github.com/nearform/fast-jwt/security/advisories/GHSA-gmvf-9v4p-v8jc | [email protected] | AdvisoryExploitRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-1391 | Use of Weak Credentials | [email protected] |
| CWE-287 | Improper Authentication | [email protected] |
| CWE-326 | Inadequate Encryption Strength | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| fast-jwt | <= 6.2.3 (semver) |
CPE
Remediation
| |
Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 14, 2026 | CVE Modified | CISA-ADP |
| May 13, 2026 | New CVE Received | [email protected] |