TI-2026-69703 Aliases CVE-2026-107719 GHSA-x937-hj6v-793p

Expired JWTs accepted from cache in fast-jwt verifier

MEDIUM 53CWE-613Published 2026-10-08 · Updated 2026-10-09

Key facts

Attack vector: Network
Privileges required: Low
User interaction: None
Attack complexity: High
Impact type: Security bypass
Confidentiality · integrity · availability: Low · Low · None
Fix status: Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-613.

Summary

fast-jwt before 6.3.4 caches verifiers that can keep accepting an expired JWT when caching is enabled and the token has exp but no iat. The cache deadline ignores exp and falls back to cacheTTL, so a cache hit returns the saved payload before expiration is rechecked (CWE-613). An attacker who can replay the same cached bearer token can extend access until the cache entry expires, but cannot forge a token.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Description from the CNA

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 6.3.4, the fast-jwt createVerifier cache can continue accepting a previously valid, signed JWT after its exp time when caching is enabled and the token has exp but no iat. In src/verifier.js, cacheSet derives the exp cache deadline only when iat is present, so the cache falls back to cacheTTL, and a later cache hit returns the saved payload before verifyToken rechecks expiration. An attacker who can replay the same cached bearer token can extend access until the cache entry expires, but cannot forge a token through this issue. This issue is fixed in version 6.3.4.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00272 19th percentileScored 2026-11-07

Fix Fixed fast-jwt (nearform): 6.3.4fast-jwt (npm): 6.3.4

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
nearform	fast-jwt	before 6.3.4	6.3.4	Patch available	CNA
—	fast-jwt (npm)	before 6.3.4	6.3.4	Patch available	GHSA-x937-hj6v-793p

fast-jwt Vendornearform Affected before 6.3.4 Fixed in 6.3.4 Patch available CNA
fast-jwt (npm) Vendor— Affected before 6.3.4 Fixed in 6.3.4 Patch available GHSA-x937-hj6v-793p

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPE	Versions	Role	Vendor
cpe:2.3:a:nearform:fast-jwt::::::::	—	—	nearform

cpe:2.3:a:nearform:fast-jwt:*:*:*:*:*:*:*:* Versions — — ·nearform

Remediation

Upgrade the npm package fast-jwt to version 6.3.4, which fixes this issue. The sources list no fixed version for nearform fast-jwt.

Written with Claude Haiku 5.5 from the sources below · 2026-10-29

Fix · CNA fast-jwt (nearform) Fixed in 6.3.4
Fix · GHSA-x937-hj6v-793p fast-jwt (npm) Fixed in 6.3.4 Advisory →

Timeline

2026-10-09 Threatist record created from CVE-2026-107719
2026-10-09 Alias added: GHSA-x937-hj6v-793p
2026-10-10 CISA SSVC decision points changed
2026-10-10 Priority changed: LOW → MEDIUM

References

Other 4

TI-2026-69702 Incomplete fix in fast-jwt enables RSA to HS256 algorithm confusion CVSS 3.1CRITICAL 9.8
TI-2026-27174 fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key CVSS 3.1CRITICAL 9.1
TI-2025-37324 get-jwks poisoned JWKS cache allows post-fetch issuer validation bypass CVSS 3.0CRITICAL 9.4
TI-2026-27245 fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation) CVSS 3.1HIGH 7.5
TI-2026-69684 Claim validator bypass in fast-jwt when JWT payload is a JSON array CVSS 3.1HIGH 8.1
TI-2026-69695 fast-jwt accepts public JWK JSON as HMAC key, enabling token forgery CVSS 3.1HIGH 7.4

See all 15 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences