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CVE-2026-107721 · GHSA-687g-22h4-j4w4

fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache)

Risk score
46/100
CVSS
5.9 v3.1
Exploit chance (30 days)
0.3%
Published
8 Oct 2026

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What to know

What it is
fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts Infinity for clockTolerance because its option validation checks type and negativity but not finiteness. In validateClaimDateValue, infinite positive and negative modifiers make exp and nbf comparisons always pa…
Affected
fast-jwt (npm) <= 6.2.4
Fix
Upgrade fast-jwt to 6.3.0 or later.
Exploitation
No known exploitation

Story map

Story map: fast-jwtTHE FLAWSTHE FIXCVE-2026-107721Fast-jwt clockTolerance:Infinity silently bypasses bothexp and nbf validation (and…CVSS 5.9 · EPSS 0%CVE-2026-107722Incomplete patch ofCVE-2026-34950:Non-whitespace key-prefix…CVSS 9.8 · EPSS 0%CVE-2026-107723Fast-jwt : Silentclaim-validator bypass whenJWT payload is a JSON arrayCVSS 8.1 · EPSS 0%CVE-2026-107720CreateVerifier acceptsunsigned JWTs when key is '' ornull and algorithms is…CVSS 7.4 · EPSS 0%Upgrade fast-jwt6.3.0 · 6.3.1or later on your release lineWho is exposedfast-jwt (npm) >= 6.2.0, <=6.2.4AMBER · PATCH THIS WEEKfast-jwtfast-jwt provides fast JSONWeb Token (JWT)implementation. From 6.2.0 until6.3.0, fast-jwt can misclassifyRSA public-key text as an HMACsecret when the key hasnon-whitespace content before…Where it standsNo known exploitationCONNECTS TOSame weaknessCWE-613 (CWE-613)34 other warnings in 30 days →
Story map: the flaws, the fix, how it unfolded and what it connects to. Boxes link to the record or article.

At a glance

fast-jwt: Amber, patch this week. fast-jwt provides fast JSON Web Token (JWT) implementation. From 6.2.0 until 6.3.0, fast-jwt can misclassify RSA public-key text as an HMAC secret when the key has non-whitespace content before its PEM header. In src/crypto.js, performDetectPublicKeyAlgorithms trims whitespace but publicKeyPemMatcher remains start-anc…

The flaws

  • CVE-2026-107721: Fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persists in the verifier cache) (CVSS 5.9 · EPSS 0%)
  • CVE-2026-107722: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion (CVSS 9.8 · EPSS 0%)
  • CVE-2026-107723: Fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array (CVSS 8.1 · EPSS 0%)
  • CVE-2026-107720: CreateVerifier accepts unsigned JWTs when key is '' or null and algorithms is explicitly set (CVSS 7.4 · EPSS 0%)

The fix

Upgrade fast-jwt: 6.3.0 · 6.3.1 or later on your release line

Who is exposed: fast-jwt (npm) >= 6.2.0, <= 6.2.4

Where it stands

  • No known exploitation

Connects to

Why it is Yellow

  • CVSS 5.9 medium
  • On your watchlist: npm

Affected packages

PackageEcosystemVulnerableFixed in
fast-jwtnpm<= 6.2.46.3.0

References

Original description

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.0, fast-jwt createVerifier accepts Infinity for clockTolerance because its option validation checks type and negativity but not finiteness. In validateClaimDateValue, infinite positive and negative modifiers make exp and nbf comparisons always pass, allowing expired or not-yet-active tokens to be accepted. The verifier cache also derives infinite bounds, so entries created under this configuration can remain valid until eviction. Exploitation requires an application administrator or equivalent configuration path to set clockTolerance to Infinity. This issue is fixed in version 6.3.0.

Last activity 8 Oct 2026. Patch Forecast updates every hour.