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CVE-2026-28802— Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification

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 1.6.5至1.6.7之前版本存在数据伪造问题漏洞，该漏洞源于传递包含alg: none和空签名的恶意JWT时通过签名验证步骤，可能导致绕过预期失败。

CVSS 7.7 · High EPSS 0.43% · P36

Affected Version Matrix 1

VendorProduct Version RangeStatus
authlib authlib >= 1.6.5, < 1.6.7 affected
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I. Basic Information for CVE-2026-28802

Vulnerability Information
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Vulnerability Title
Authlib: Setting `alg: none` and a blank signature appears to bypass signature verification
Source: CVE Program / CVE List V5
Vulnerability Description
Authlib is a Python library which builds OAuth and OpenID Connect servers. From version 1.6.5 to before version 1.6.7, previous tests involving passing a malicious JWT containing alg: none and an empty signature was passing the signature verification step without any changes to the application code when a failure was expected.. This issue has been patched in version 1.6.7.
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/E:P
Source: CVE Program / CVE List V5
Vulnerability Type
密码学签名的验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Authlib 数据伪造问题漏洞
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 1.6.5至1.6.7之前版本存在数据伪造问题漏洞，该漏洞源于传递包含alg: none和空签名的恶意JWT时通过签名验证步骤，可能导致绕过预期失败。
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 >= 1.6.5, < 1.6.7 -

II. Public POCs for CVE-2026-28802

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 10806 chars
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III. Intelligence Information for CVE-2026-28802

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Patches & Fixes for CVE-2026-28802 (2)

Vendor Advisories for CVE-2026-28802 (1)

IV. Related Vulnerabilities

Same product: authlib
Same vendor: authlib
Same weakness: CWE-347

V. Comments for CVE-2026-28802

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