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CVE-2026-27199— Werkzeug safe_join() allows Windows special device names

Quick assessment

Affected
pallets werkzeug
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.

Werkzeug是Pallets开源的一个全面的 WSGI web 应用程序库。 Werkzeug 3.1.5及之前版本存在安全漏洞，该漏洞源于safe_join函数允许Windows设备名作为文件名，可能导致拒绝服务。

AI Predicted 7.5 Difficulty: Easy EPSS 0.54% · P44
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I. Basic Information for CVE-2026-27199

Vulnerability Information
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Vulnerability Title
Werkzeug safe_join() allows Windows special device names
Source: CVE Program / CVE List V5
Vulnerability Description
Werkzeug is a comprehensive WSGI web application library. Versions 3.1.5 and below, the safe_join function allows Windows device names as filenames if preceded by other path segments. This was previously reported as GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact that safe_join accepts paths with multiple segments, such as example/NUL. The function send_from_directory uses safe_join to safely serve files at user-specified paths under a directory. If the application is running on Windows, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely. This issue has been fixed in version 3.1.6.
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及之前版本存在安全漏洞，该漏洞源于safe_join函数允许Windows设备名作为文件名，可能导致拒绝服务。
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 < 3.1.6 -

II. Public POCs for CVE-2026-27199

# POC Description Source Link Shenlong Link
1 None https://github.com/alimezar/CVE-2026-27199-werkzeug-safe-join-bypass-PoC POC Details
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III. Intelligence Information for CVE-2026-27199

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IV. Related Vulnerabilities

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

V. Comments for CVE-2026-27199

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