TI-2025-21484 Aliases CVE-2025-30144 GHSA-gm45-q3v2-6cf8

Fast-JWT Improperly Validates iss Claims

MEDIUM 62CWE-290Published 2025-03-19 · Updated 2025-03-19

Key facts

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

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-290.

Summary

fast-jwt provides fast JSON Web Token (JWT) implementation. Prior to 5.0.6, the fast-jwt library does not properly validate the iss claim based on the RFC 7519. The iss (issuer) claim validation within the fast-jwt library permits an array of strings as a valid iss value. This design flaw enables a potential attack where a malicious actor crafts a JWT with an iss claim structured as ['https://attacker-domain/', 'https://valid-iss']. Due to the permissive validation, the JWT will be deemed valid. Furthermore, if the application relies on external libraries like get-jwks that do not independently validate the iss claim, the attacker can leverage this vulnerability to forge a JWT that will be accepted by the victim application. Essentially, the attacker can insert their own domain into the iss array, alongside the legitimate issuer, and bypass the intended security checks. This issue is fixed in 5.0.6.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00592 48th percentileScored 2026-11-07

Fix Fixed fast-jwt (nearform): 5.0.6fast-jwt (npm): 5.0.6

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 5.0.6	5.0.6	Patch available	CNA
—	fast-jwt (npm)	before 5.0.6	5.0.6	Patch available	GHSA-gm45-q3v2-6cf8

fast-jwt Vendornearform Affected before 5.0.6 Fixed in 5.0.6 Patch available CNA
fast-jwt (npm) Vendor— Affected before 5.0.6 Fixed in 5.0.6 Patch available GHSA-gm45-q3v2-6cf8

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

Fix · CNA fast-jwt (nearform) Fixed in 5.0.6
Fix · GHSA-gm45-q3v2-6cf8 fast-jwt (npm) Fixed in 5.0.6 Advisory →

Timeline

2026-10-02 Threatist record created from CVE-2025-30144
2026-10-03 Alias added: GHSA-gm45-q3v2-6cf8

References

Advisory 1

https://nvd.nist.gov/vuln/detail/CVE-2025-30144

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