Goal Reached Thanks to every supporter — we hit 100%!

Goal: 1000 CNY · Raised: 1336 CNY

100%
Buy Us a Coffee

CVE-2026-35042— fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)

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。

CVSS 7.5 · High EPSS 0.15% · P5

Possible ATT&CK Techniques 1 AI

T1550 · Use Alternate Authentication Material
Get alerts for future matching vulnerabilities Log in to subscribe

I. Basic Information for CVE-2026-35042

Vulnerability Information
Have questions about the vulnerability? See if Shenlong's analysis helps!
View Shenlong Deep Dive ↗

Although we use advanced large model technology, its output may still contain inaccurate or outdated information.Shenlong tries to ensure data accuracy, but please verify and judge based on the actual situation.

Vulnerability Title
fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)
Source: CVE Program / CVE List V5
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: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对数据真实性的验证不充分
Source: CVE Program / CVE List V5
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

Vendor Product Affected Versions CPE Subscribe
nearform fast-jwt <= 6.1.0 -

II. Public POCs for CVE-2026-35042

# POC Description Source Link Shenlong Link
AI-Generated POC Premium

No public POC found.

Login to generate AI POC

III. Intelligence Information for CVE-2026-35042

请登录查看更多情报信息。

Vendor Advisories for CVE-2026-35042 (1)

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
Same vendor: nearform
Same weakness: CWE-345

V. Comments for CVE-2026-35042

No comments yet

Leave a comment