CVE-2026-34950— fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key
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I. Basic Information for CVE-2026-34950
Vulnerability Information
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Vulnerability Title
fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace-Prefixed RSA Public Key
Source: NVD (National Vulnerability Database)
Vulnerability Description
fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, the publicKeyPemMatcher regex in fast-jwt/src/crypto.js uses a ^ anchor that is defeated by any leading whitespace in the key string, re-enabling the exact same JWT algorithm confusion attack that CVE-2023-48223 patched.
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: NVD (National Vulnerability Database)
Vulnerability Type
使用已被攻破或存在风险的密码学算法
Source: NVD (National Vulnerability Database)
Vulnerability Title
fast-jwt 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
fast-jwt是Nearform开源的一个 JSON Web Token 实现。 fast-jwt 6.1.0及之前版本存在加密问题漏洞，该漏洞源于publicKeyPemMatcher正则表达式的^锚定符可被密钥字符串中的前导空格绕过，可能导致JWT算法混淆攻击。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
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Affected Products
II. Public POCs for CVE-2026-34950
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Same Patch Batch · nearform · 2026-04-06 · 3 CVEs total
| CVE-2026-35039 | 9.1 CRITICAL | fast-jwt Affected by Cache Confusion via cacheKeyBuilder Collisions Can Return Claims From |
| CVE-2026-35042 | 7.5 HIGH | fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation) |
IV. Related Vulnerabilities
Same product: fast-jwt
- CVE-2026-35041
ReDoS in fast-jwt when using RegExp in allowed* leading to C - CVE-2026-35040
fast-jwt: Stateful RegExp (/g or /y) causes non-deterministi - CVE-2026-35042
fast-jwt accepts unknown `crit` header extensions (RFC 7515 - CVE-2026-35039
fast-jwt Affected by Cache Confusion via cacheKeyBuilder Col - CVE-2025-30144
Fast-JWT Improperly Validates iss Claims
Same vendor: nearform
- CVE-2026-35041
ReDoS in fast-jwt when using RegExp in allowed* leading to C - CVE-2026-35040
fast-jwt: Stateful RegExp (/g or /y) causes non-deterministi - CVE-2026-35042
fast-jwt accepts unknown `crit` header extensions (RFC 7515 - CVE-2026-35039
fast-jwt Affected by Cache Confusion via cacheKeyBuilder Col - CVE-2025-59936
get-jwks poisoned JWKS cache allows post-fetch issuer valida
Same weakness: CWE-327
- CVE-2026-6411
MAXHUB Pivot Client Application Use of a Broken or Risky Cry - CVE-2026-44405
Paramiko 加密问题漏洞 - CVE-2026-32959
Silex SD-330AC和Silex AMC Manager 安全漏洞 - CVE-2026-5588
PKIX draft CompositeVerifier accepts empty signature sequenc - CVE-2025-14813
GOSTCTR implementation unable to process more than 255 block
V. Comments for CVE-2026-34950
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