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CVE-2026-49852— joserfc: HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363)

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 1.6.8之前版本存在安全漏洞，该漏洞源于HMAC签名验证时未拒绝零长度密钥输入，导致调用者提供的验证密钥为空字符串或None时接受攻击者伪造的HMAC签名令牌。

AI Predicted 9.1 Difficulty: Easy EPSS 0.19% · P8

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
authlib joserfc < 1.6.8 affected
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I. Basic Information for CVE-2026-49852

Vulnerability Information
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Vulnerability Title
joserfc: HS256/HS384/HS512 verify accepts empty/nil HMAC key (cross-language sibling of CVE-2026-45363)
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 1.6.8, joserfc.jwt.decode accepts attacker-forged HMAC-signed tokens when the caller-supplied verification key is the empty string or None, because HMACAlgorithm.sign and HMACAlgorithm.verify in src/joserfc/_rfc7518/jws_algs.py pass the output of OctKey.get_op_key(...) to hmac.new(...) and OctKey.import_key in src/joserfc/_rfc7518/oct_key.py only emits a SecurityWarning for keys shorter than 14 bytes without rejecting zero-length input. This issue is fixed in version 1.6.8.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
认证机制不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Authlib joserfc 信任管理问题漏洞
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 1.6.8之前版本存在安全漏洞，该漏洞源于HMAC签名验证时未拒绝零长度密钥输入，导致调用者提供的验证密钥为空字符串或None时接受攻击者伪造的HMAC签名令牌。
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
authlib joserfc < 1.6.8 -

II. Public POCs for CVE-2026-49852

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III. Intelligence Information for CVE-2026-49852

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Patches & Fixes for CVE-2026-49852 (2)

Vendor Advisories for CVE-2026-49852 (1)

IV. Related Vulnerabilities

Same product: joserfc
Same vendor: authlib
Same weakness: CWE-287

V. Comments for CVE-2026-49852

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