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CVE-2026-75509— joserfc claim-validation bypass via array-typed single-string claims (iss/sub/jti)

Quick assessment

Affected
authlib joserfc
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.

Authlib joserfc是Authlib组织开源的一个 Python 库，全面实现了 JOSE（JSON Object Signing and Encryption）系列标准，包括 JWS、JWE、JWK、JWT 等 RFC 规范，用于安全地处理 JSON 数据的签名与加密。 Authlib joserfc 1.7.3之前版本存在安全漏洞，该漏洞源于JWTClaimsRegistry对列表值iss和sub声明应用成员匹配，允许包含预期签发者的数组值iss通过预期相等检查，导致签发者验证绕过。

CVSS 6.5 · Medium EPSS 0.12% · P2

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
authlib joserfc < 1.7.3 affected
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I. Basic Information for CVE-2026-75509

Vulnerability Information
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Vulnerability Title
joserfc claim-validation bypass via array-typed single-string claims (iss/sub/jti)
Source: CVE Program / CVE List V5
Vulnerability Description
joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to version 1.7.3, JWTClaimsRegistry applies membership matching to list-valued iss and sub claims, allowing an array-valued iss that contains the expected issuer to pass an intended equality check and enabling issuer-validation bypass. This issue is fixed in version 1.7.3.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5
Vulnerability Title
Authlib joserfc 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Authlib joserfc是Authlib组织开源的一个 Python 库，全面实现了 JOSE（JSON Object Signing and Encryption）系列标准，包括 JWS、JWE、JWK、JWT 等 RFC 规范，用于安全地处理 JSON 数据的签名与加密。 Authlib joserfc 1.7.3之前版本存在安全漏洞，该漏洞源于JWTClaimsRegistry对列表值iss和sub声明应用成员匹配，允许包含预期签发者的数组值iss通过预期相等检查，导致签发者验证绕过。
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
authlib joserfc < 1.7.3 -

II. Public POCs for CVE-2026-75509

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III. Intelligence Information for CVE-2026-75509

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Patches & Fixes for CVE-2026-75509 (1)

Vendor Advisories for CVE-2026-75509 (1)

IV. Related Vulnerabilities

Same product: joserfc
Same vendor: authlib
Same weakness: CWE-290

V. Comments for CVE-2026-75509

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