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CVE-2025-66221

Werkzeug safe_join() allows Windows special device names

6.3 MediumFix available

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 3.1.4.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
None
Availability
Low

Exploit likelihood

0.55%Up 0.5 points since Nov 29, 2025
90%50%10%1%

What each source reports

CVE List Score used 6.3

Werkzeug safe_join() allows Windows special device names

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 3.1.4.

Record
CVE-2025-66221
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Weakness
CWE-67
Updated
2026-11-02
EUVDEUVD-2025-199893 6.3

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 3.1.4.

Record
EUVD-2025-199893
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-hgf8-39gv-g3f2 6.3

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.

Record
GHSA-hgf8-39gv-g3f2
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Weakness
CWE-67
Updated
2026-11-02
NVD 6.3

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 3.1.4.

Record
CVE-2025-66221
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness
CWE-67
Updated
2026-11-02
OSVALPINE-CVE-2025-66221 5.3

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 3.1.4.

Record
ALPINE-CVE-2025-66221
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-02
OSVBELL-CVE-2025-66221 5.3

CVE-2025-66221 does not affect BellSoft software

Record
BELL-CVE-2025-66221
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-02
Show 9 moreShow less
OSV 6.3

Werkzeug safe_join() allows Windows special device names

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 3.1.4.

Record
CVE-2025-66221
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Weakness
CWE-67
Updated
2026-11-02
OSVGHSA-hgf8-39gv-g3f2 6.3

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.

Record
GHSA-hgf8-39gv-g3f2
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Weakness
CWE-67
Updated
2026-11-02
OSVPYSEC-2026-2046 6.3

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.

Record
PYSEC-2026-2046
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Updated
2026-11-02
OSVROOT-APP-PYPI-CVE-2025-66221 5.3

CVE-2025-66221 in rootio-Werkzeug - Patched by Root

Root has patched CVE-2025-66221 in the rootio-Werkzeug package for Root:PyPI. Multiple fixed versions available.

Record
ROOT-APP-PYPI-CVE-2025-66221
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-02
OSVUBUNTU-CVE-2025-66221 6.3

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 3.1.4.

Record
UBUNTU-CVE-2025-66221
CVSS 4.0
6.3 MediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
CVSS 3.1
5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Updated
2026-11-02
OSVCLSA-2026-1772583182 No score

TuxCare security update for werkzeug (1 CVE)

TuxCare rebuilt werkzeug to address 1 CVE. Fixed in 2.3.8.post1+tuxcare.

Record
CLSA-2026-1772583182
Updated
2026-11-02
OSVCLSA-2026-1789365574 No score

TuxCare security update for werkzeug (1 CVE)

TuxCare rebuilt werkzeug to address 1 CVE. Fixed in 1.0.1.post5+tuxcare.

Record
CLSA-2026-1789365574
Updated
2026-11-02
OSVCLSA-2026-1791365297 No score

TuxCare security update for werkzeug (2 CVEs)

TuxCare rebuilt werkzeug to address 2 CVEs. Fixed in 2.2.3.post6+tuxcare.

Record
CLSA-2026-1791365297
Updated
2026-11-02
OSVopenSUSE-SU-2025:15848-1 No score

python311-openapi-core-0.22.0-1.1 on GA media

These are all security issues fixed in the python311-openapi-core-0.22.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2025:15848-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
werkzeug
PyPI
 before 3.1.4
3.1.4
py3-werkzeug
Alpine:v3.24
 before 3.1.4-r0
3.1.4-r0
werkzeug
TuxCare:PyPI
 2.3.8 up to 2.3.8.post1+tuxcare
2.3.8.post1+tuxcare
werkzeug
TuxCare:PyPI
 1.0.1 up to 1.0.1.post5+tuxcare, plus listed versions
1.0.1.post1+tuxcare1.0.1.post2+tuxcare1.0.1.post3+tuxcare1.0.1.post4+tuxcare
1.0.1.post5+tuxcare
werkzeug
TuxCare:PyPI
From an advisory covering 2 CVEs
 2.2.3 up to 2.2.3.post6+tuxcare, plus listed versions
2.2.3.post1+tuxcare2.2.3.post3+tuxcare2.2.3.post4+tuxcare2.2.3.post5+tuxcare
2.2.3.post6+tuxcare
werkzeug
PyPI
 before 3.1.4, plus listed versions
0.10.100.10.10.10.20.10.3
Show 45 moreShow less
0.10.40.110.11.10.11.100.11.110.11.120.11.130.11.140.11.150.11.20.11.30.11.40.11.50.11.60.11.70.11.80.11.90.120.12.10.12.20.130.140.14.10.15.00.15.10.15.20.15.30.15.40.15.50.15.60.16.00.16.10.20.30.3.10.40.4.10.50.5.10.60.6.10.6.20.70.7.10.7.2
3.1.4
rootio-Werkzeug
Root:PyPI
 before 2.3.7+root.io.5
2.3.7+root.io.53.1.3+root.io.33.1.3+root.io.42.3.7+root.io.63.1.0+root.io.1
Werkzeug
Root:PyPI
 before 3.1.3+aikido.4
3.1.3+aikido.42.3.7+aikido.6
python-openapi-core
openSUSE:Tumbleweed
 before 0.22.0-1.1
0.22.0-1.1

History

History
RecordedChangedSources
affected, facts
affected
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2025-66221 is a medium vulnerability (CVSS 6.3) in Pallets Werkzeug, published November 29, 2025. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.55%, the 46th percentile. Fixed in werkzeug 3.1.4.

References

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Left out here: 51 versions. The JSON record has them.

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