High · CVSS 8.1CVE-2026-107723GHSA-5HJW-83FP-PHQ9

fast-jwt : Silent claim-validator bypass when JWT payload is a JSON arrayCVE-2026-107723

Answer in brief

CVE-2026-107723 records a High severity (CVSS 8.1) vulnerability in fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array. The current sources do not mark it as known exploited. The current feed maps nearform/fast-jwt (generic), fast-jwt (npm), fast-jwt (npm). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 8, 2026Updated Oct 8, 2026Source checked Oct 8, 2026First seen by HOL Oct 8, 2026Material review Oct 8, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 8.1
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 8.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps nearform/fast-jwt (generic), fast-jwt (npm), fast-jwt (npm). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
nearform/fast-jwtgeneric	<6.3.0	6.3.0
fast-jwtnpm	<=6.2.4	6.3.0
fast-jwtnpm	>=0 <6.3.0	6.3.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for nearform/fast-jwt, fast-jwt, fast-jwt.
Review the reported fix. Update nearform/fast-jwt to 6.3.0; fast-jwt to 6.3.0; fast-jwt to 6.3.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 8, 2026

Sources and claim methodology

Upstream source description

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts a validly signed JWT whose payload is a JSON array because src/decoder.js checks that the payload is an object but does not reject arrays. The claim validator loop then finds no named exp, nbf, iss, aud, sub, jti, or nonce properties and silently skips those configured checks, returning the array as a successfully verified payload. An attacker who can produce or influence a validly signed token may bypass expiry, issuer, audience, subject, revocation, and replay protections. The opt-in requiredClaims option can block missing claims, and signature verification itself is not bypassed. This issue is fixed in version 6.3.0.

Quoted source text, attributed separately from HOL analysis.