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CVE-2026-21860— Werkzeug safe_join() allows Windows special device names with compound extensions

Quick assessment

Affected
pallets werkzeug
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.

Werkzeug是Pallets开源的一个全面的 WSGI web 应用程序库。 Werkzeug 3.1.5之前版本存在安全漏洞，该漏洞源于safe_join函数允许包含Windows设备名称的路径段，可能导致安全问题。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.48% · P39

Possible ATT&CK Techniques 1 AI

T1564.004 · NTFS File Attributes
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I. Basic Information for CVE-2026-21860

Vulnerability Information
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Vulnerability Title
Werkzeug safe_join() allows Windows special device names with compound extensions
Source: CVE Program / CVE List V5
Vulnerability Description
Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.5, Werkzeug's safe_join function allows path segments with Windows device names that have file extensions or trailing spaces. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. Windows still accepts them with any file extension, such as CON.txt, or trailing spaces such as CON. This issue has been patched in version 3.1.5.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
Windows设备名处理不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Werkzeug 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Werkzeug是Pallets开源的一个全面的 WSGI web 应用程序库。 Werkzeug 3.1.5之前版本存在安全漏洞，该漏洞源于safe_join函数允许包含Windows设备名称的路径段，可能导致安全问题。
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
pallets werkzeug < 3.1.5 -

II. Public POCs for CVE-2026-21860

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III. Intelligence Information for CVE-2026-21860

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Vendor Advisories for CVE-2026-21860 (1)

IV. Related Vulnerabilities

Same product: werkzeug
Same vendor: pallets
Same weakness: CWE-67

V. Comments for CVE-2026-21860

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