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Vulnerabilities

Security fix · CVE-2025-66221

Werkzeug is a comprehensive WSGI web application library.

Published Nov 29, 2025 · catalog updated Dec 1, 2025 · Werkzeug is a comprehensive

Last checked Nov 2, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2025-66221. EPSS is 0.55%. Act only if a listed version of Werkzeug is a comprehensive is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Werkzeug is a comprehensive).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
Medium6.3
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.55%
Remediation
Version ranges on file
Affected products
vendor pallets werkzeug < 3.1.4

Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.4, 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. This issue has been patched in version 3.1

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor pallets werkzeug < 3.1.4< 3.1.4

How to fix CVE-2025-66221

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-66221. EPSS is 0.55%. Act only if a listed version of Werkzeug is a comprehensive is installed.

Which versions are affected?

Compare what you have installed with pallets werkzeug < 3.1.4 < 3.1.4. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.55%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Nov 29, 2025 · EUVD

    Detected

    Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.4, 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 applica

  2. Dec 1, 2025 · EUVD

    Updated

    Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.4, 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 applica

Sources

  • CVE.orgVulnerability recordCVE-2025-66221

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-66221

    30-day exploitation probability 0.55%

    first.org
  • EUVDVulnerability recordEUVD-2025-199893

    Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.4, 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 direc

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Nov 2, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 2, 2026
  • CVE.orgOct 28, 2026
  • EUVDOct 28, 2026