N/A

CVSS Score

-

CVSS Score

Basic Information

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CVE-2025-66221

CVE-2025-66221: Werkzeug safe_join() allows Windows special device names

Werkzeug's safe_join function allows path segments with Windows device names. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. 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.

(GitHub Advisory)

Miggo Vulnerability Database

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CVE-2025-66221

CVE-2025-66221:

N/A

CVSS Score

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
werkzeug	pip	< 3.1.4	3.1.4

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability exists in the safe_join function located in src/werkzeug/security.py. This function did not properly sanitize user-provided filenames to prevent the use of reserved Windows device names such as 'CON', 'AUX', or 'PRN'. The patch, found in commit 4b833376a45c323a189cd11d2362bcffdb1c0c13, adds a specific check for these device names when the operating system is Windows (os.name == 'nt'). The vulnerability is typically exploited through the send_from_directory function, which uses safe_join to construct the path to the file being served. By requesting a file with a special device name, an attacker can cause the application to hang when send_from_directory attempts to read from the device, leading to a Denial of Service. A runtime profile of an exploit would show send_from_directory calling the vulnerable safe_join function.

Vulnerable functions

Only Mi**o us*rs **n s** t*is s**tion

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WAF Protection Rules

WAF Rule

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Reasoning

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