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CVE-2026-35039— fast-jwt Affected by Cache Confusion via cacheKeyBuilder Collisions Can Return Claims From a Different Token (Identity/Authorization Mixup)

Quick assessment

Affected
nearform fast-jwt
Exploitation
Public or AI PoC available; prioritize validation
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之前版本存在安全漏洞，该漏洞源于自定义cacheKeyBuilder方法未正确创建唯一密钥，可能导致缓存冲突和用户身份误认。

CVSS 9.1 · Critical EPSS 0.22% · P11

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
nearform fast-jwt >= 0.0.1, < 6.2.0 affected
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I. Basic Information for CVE-2026-35039

Vulnerability Information
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Vulnerability Title
fast-jwt Affected by Cache Confusion via cacheKeyBuilder Collisions Can Return Claims From a Different Token (Identity/Authorization Mixup)
Source: CVE Program / CVE List V5
Vulnerability Description
fast-jwt provides fast JSON Web Token (JWT) implementation. From 0.0.1 to before 6.2.0, setting up a custom cacheKeyBuilder method which does not properly create unique keys for different tokens can lead to cache collisions. This could cause tokens to be mis-identified during the verification process leading to valid tokens returning claims from different valid tokens and users being mis-identified as other users based on the wrong token. Version 6.2.0 contains a patch.
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: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之前版本存在安全漏洞，该漏洞源于自定义cacheKeyBuilder方法未正确创建唯一密钥，可能导致缓存冲突和用户身份误认。
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

Vendor Product Affected Versions CPE Subscribe
nearform fast-jwt >= 0.0.1, < 6.2.0 -

II. Public POCs for CVE-2026-35039

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 8880 chars
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III. Intelligence Information for CVE-2026-35039

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Patches & Fixes for CVE-2026-35039 (1)

Vendor Advisories for CVE-2026-35039 (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-2026-35042 7.5 HIGH fast-jwt accepts unknown `crit` header extensions (RFC 7515 §4.1.11 MUST violation)

IV. Related Vulnerabilities

Same product: fast-jwt
Same vendor: nearform
Same weakness: CWE-345

V. Comments for CVE-2026-35039

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