CVE-2026-35042— fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)
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I. Basic Information for CVE-2026-35042
Vulnerability Information
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Vulnerability Title
fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)
Source: NVD (National Vulnerability Database)
Vulnerability Description
fast-jwt provides fast JSON Web Token (JWT) implementation. In 6.1.0 and earlier, fast-jwt does not validate the crit (Critical) Header Parameter defined in RFC 7515 §4.1.11. When a JWS token contains a crit array listing extensions that fast-jwt does not understand, the library accepts the token instead of rejecting it. This violates the MUST requirement in the RFC.
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: NVD (National Vulnerability Database)
Vulnerability Type
对数据真实性的验证不充分
Source: NVD (National Vulnerability Database)
Vulnerability Title
fast-jwt 安全漏洞
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及之前版本存在安全漏洞，该漏洞源于未验证crit头部参数，可能导致接受包含未知扩展的令牌。
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)
Affected Products
II. Public POCs for CVE-2026-35042
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Same Patch Batch · nearform · 2026-04-06 · 3 CVEs total
| CVE-2026-34950 | 9.1 CRITICAL | fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algorithm Confusion via Whitespace- |
| CVE-2026-35039 | 9.1 CRITICAL | fast-jwt Affected by Cache Confusion via cacheKeyBuilder Collisions Can Return Claims From |
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-2026-35039
fast-jwt Affected by Cache Confusion via cacheKeyBuilder Col - CVE-2026-34950
fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algor - 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-2026-35039
fast-jwt Affected by Cache Confusion via cacheKeyBuilder Col - CVE-2026-34950
fast-jwt has an incomplete fix for CVE-2023-48223: JWT Algor - CVE-2025-59936
get-jwks poisoned JWKS cache allows post-fetch issuer valida
Same weakness: CWE-345
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apko doesn't verify downloaded apk packages against APKINDEX - CVE-2026-41432
New API: Stripe Webhook Signature Bypass via Empty Secret En - CVE-2026-42206
Roadiz OpenID Connect nonce generated but never validated — - CVE-2026-31835
Vaultwarden WebAuthn credential metadata tampered before sig - CVE-2026-43534
OpenClaw < 2026.4.10 - Unsanitized External Input in Agent H
V. Comments for CVE-2026-35042
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