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CVE-2026-107722— fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion

Quick assessment

Affected
nearform fast-jwt
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

fast-jwt 是一个高性能的 JSON Web Token（JWT）实现库。在版本 6.2.0 至 6.3.0 之间，当 RSA 公钥文本在其 PEM 头部之前包含非空白内容时，fast-jwt 可能错误地将该 RSA 公钥识别为 HMAC 密钥。 在 文件中， 函数会对输入进行空白字符修剪，但 正则表达式仍是从头开始匹配的（start-anchored）。因此，注释、控制字符、零宽字符或包装文本等前缀内容会阻止 PEM 格式的识别，从而导致系统回退到 HMAC 密钥处理逻辑。 如果 HS256 算法被推断为可

CVSS 9.8 · Critical
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I. Basic Information for CVE-2026-107722

Vulnerability Information
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Vulnerability Title
fast-jwt: Incomplete patch of CVE-2026-34950: Non-whitespace key-prefix re-enables RSA→HS256 algorithm confusion
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
密码学签名的验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
nearform fast-jwt >= 6.2.0, < 6.3.0 -

II. Public POCs for CVE-2026-107722

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III. Intelligence Information for CVE-2026-107722

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Patches & Fixes for CVE-2026-107722 (2)

Vendor Advisories for CVE-2026-107722 (1)

Vendor Pages for CVE-2026-107722 (1)

Same Patch Batch · nearform · 2026-10-08 · 6 CVEs total

CVE-2026-107723 8.1 HIGH fast-jwt : Silent claim-validator bypass when JWT payload is a JSON array
CVE-2026-107720 7.4 HIGH fast-jwt: createVerifier accepts unsigned JWTs when key is '' or null and algorithms is ex
CVE-2026-107724 7.4 HIGH fast-jwt treats raw public JWK JSON as an HMAC secret, enabling HS256 token forgery
CVE-2026-107721 5.9 MEDIUM fast-jwt clockTolerance: Infinity silently bypasses both exp and nbf validation (and persi
CVE-2026-107719 4.2 MEDIUM fast-jwt: Verifier cache accepts expired JWTs without iat.

IV. Related Vulnerabilities

Same product: fast-jwt
Same vendor: nearform
Same weakness: CWE-347

V. Comments for CVE-2026-107722

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