TI-2026-69702 Aliases CVE-2026-107722 GHSA-ww5h-9m49-7xx4

Incomplete fix in fast-jwt enables RSA to HS256 algorithm confusion

HIGH 82CWE-347Published 2026-10-08 · Updated 2026-10-13

Key facts

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

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-347.

Summary

fast-jwt from 6.2.0 before 6.3.0 can treat RSA public key text as an HMAC secret. Non-whitespace content before the PEM header stops key detection and falls back to HMAC (CWE-347). A remote attacker who knows the public key can forge HS256 tokens when HS256 is inferred or allowed, bypassing authentication or authorization.

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. 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-anchored, so comments, control characters, zero-width characters, or wrapper text can prevent PEM detection and reach the HMAC fallback. An attacker who knows the public key bytes can sign arbitrary HS256 claims with that public material when HS256 is inferred or allowed, resulting in authentication or authorization bypass. An asymmetric-only algorithm allowlist prevents the attack. This issue is fixed in version 6.3.0.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00356 29th percentileScored 2026-11-07

Fix Fixed fast-jwt (nearform): 6.3.0fast-jwt (npm): 6.3.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: Yes
Technical impact: Total

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	6.2.0 to before 6.3.0	6.3.0	Patch available	CNA
—	fast-jwt (npm)	6.2.0 to before 6.3.0	6.3.0	Patch available	GHSA-ww5h-9m49-7xx4

fast-jwt Vendornearform Affected 6.2.0 to before 6.3.0 Fixed in 6.3.0 Patch available CNA
fast-jwt (npm) Vendor— Affected 6.2.0 to before 6.3.0 Fixed in 6.3.0 Patch available GHSA-ww5h-9m49-7xx4

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 6.3.0, which fixes this issue. Until the upgrade, an asymmetric-only algorithm allowlist prevents the attack.

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

Fix · CNA fast-jwt (nearform) Fixed in 6.3.0
Fix · GHSA-ww5h-9m49-7xx4 fast-jwt (npm) Fixed in 6.3.0 Advisory →

Timeline

2026-10-09 Threatist record created from CVE-2026-107722
2026-10-09 Alias added: GHSA-ww5h-9m49-7xx4
2026-10-13 CISA SSVC decision points changed
2026-10-13 Priority changed: MEDIUM → HIGH

References

Other 5

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
TI-2026-69689 fast-jwt accepts unsigned JWTs when the key is empty or null 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