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CVE-2026-35041— ReDoS in fast-jwt when using RegExp in allowed* leading to CPU exhaustion during token verification

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 6.2.0及之前版本存在安全漏洞，该漏洞源于allowedAud验证选项使用正则表达式时，攻击者控制的aud声明可能触发灾难性回溯，导致验证期间CPU消耗过高。

CVSS 4.2 · Medium EPSS 0.43% · P35

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking
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I. Basic Information for CVE-2026-35041

Vulnerability Information
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Vulnerability Title
ReDoS in fast-jwt when using RegExp in allowed* leading to CPU exhaustion during token verification
Source: CVE Program / CVE List V5
Vulnerability Description
fast-jwt provides fast JSON Web Token (JWT) implementation. From 5.0.0 to 6.2.0, a denial-of-service condition exists in fast-jwt when the allowedAud verification option is configured using a regular expression. Because the aud claim is attacker-controlled and the library evaluates it against the supplied RegExp, a crafted JWT can trigger catastrophic backtracking in the JavaScript regex engine, resulting in significant CPU consumption during verification. This vulnerability is fixed in 6.2.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1333
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 6.2.0及之前版本存在安全漏洞，该漏洞源于allowedAud验证选项使用正则表达式时，攻击者控制的aud声明可能触发灾难性回溯，导致验证期间CPU消耗过高。
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 >= 5.0.0, < 6.2.1 -

II. Public POCs for CVE-2026-35041

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III. Intelligence Information for CVE-2026-35041

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Patches & Fixes for CVE-2026-35041 (2)

Vendor Advisories for CVE-2026-35041 (1)

IV. Related Vulnerabilities

Same product: fast-jwt
Same vendor: nearform
Same weakness: CWE-1333

V. Comments for CVE-2026-35041

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