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CVE-2026-28498— Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding

Quick assessment

Affected
authlib authlib
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.

Authlib是Authlib开源的一个构建 OAuth 和 OpenID Connect 服务器的终极 Python 库。 Authlib 1.6.9之前版本存在安全漏洞，该漏洞源于OpenID Connect ID令牌验证逻辑存在失败开放行为，可能导致攻击者通过提供伪造令牌绕过完整性保护。

CVSS 8.2 · High EPSS 0.26% · P16

Affected Version Matrix 1

VendorProduct Version RangeStatus
authlib authlib < 1.6.9 affected
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I. Basic Information for CVE-2026-28498

Vulnerability Information
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Vulnerability Title
Authlib: Fail-Open Cryptographic Verification in OIDC Hash Binding
Source: CVE Program / CVE List V5
Vulnerability Description
Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to version 1.6.9, a library-level vulnerability was identified in the Authlib Python library concerning the validation of OpenID Connect (OIDC) ID Tokens. Specifically, the internal hash verification logic (_verify_hash) responsible for validating the at_hash (Access Token Hash) and c_hash (Authorization Code Hash) claims exhibits a fail-open behavior when encountering an unsupported or unknown cryptographic algorithm. This flaw allows an attacker to bypass mandatory integrity protections by supplying a forged ID Token with a deliberately unrecognized alg header parameter. The library intercepts the unsupported state and silently returns True (validation passed), inherently violating fundamental cryptographic design principles and direct OIDC specifications. This issue has been patched in version 1.6.9.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
完整性检查值验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Authlib 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Authlib是Authlib开源的一个构建 OAuth 和 OpenID Connect 服务器的终极 Python 库。 Authlib 1.6.9之前版本存在安全漏洞，该漏洞源于OpenID Connect ID令牌验证逻辑存在失败开放行为，可能导致攻击者通过提供伪造令牌绕过完整性保护。
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 authlib < 1.6.9 -

II. Public POCs for CVE-2026-28498

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Qwen3.6-35B-A3B · 9322 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
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Trigger conditions & impact
Full executable POC code
Exploit chain & mitigation
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III. Intelligence Information for CVE-2026-28498

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Patches & Fixes for CVE-2026-28498 (1)

Vendor Advisories for CVE-2026-28498 (1)

Vendor Pages for CVE-2026-28498 (1)

Same Patch Batch · authlib · 2026-03-16 · 3 CVEs total

CVE-2026-27962 9.1 CRITICAL Authlib JWS JWK Header Injection: Signature Verification Bypass
CVE-2026-28490 Authlib Vulnerable to JWE RSA1_5 Bleichenbacher Padding Oracle

IV. Related Vulnerabilities

Same product: authlib
Same vendor: authlib
Same weakness: CWE-354

V. Comments for CVE-2026-28498

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