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CVE-2026-27199

Werkzeug safe_join() allows Windows special device names

6.3 MediumPublic exploitFix available

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.

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

0.63%Up 0.6 points since Feb 21, 2026
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. 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.

Record
CVE-2026-27199
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-2026-7732 6.3

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.

Record
EUVD-2026-7732
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-29vq-49wr-vm6x 6.3

Werkzeug safe_join() allows Windows special device names

Werkzeug's safe_join function allows Windows device names as filenames if when preceded by other path segments.

This was previously reported as https://github.com/pallets/werkzeug/security/advisories/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.

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-29vq-49wr-vm6x
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. 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.

Record
CVE-2026-27199
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-2026-27199 5.3

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.

Record
ALPINE-CVE-2026-27199
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-2026-27199 5.3

CVE-2026-27199 does not affect BellSoft software

Record
BELL-CVE-2026-27199
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 7 moreShow less
OSV 6.3

Werkzeug safe_join() allows Windows special device names

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.

Record
CVE-2026-27199
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-29vq-49wr-vm6x 6.3

Werkzeug safe_join() allows Windows special device names

Werkzeug's safe_join function allows Windows device names as filenames if when preceded by other path segments.

This was previously reported as https://github.com/pallets/werkzeug/security/advisories/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.

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-29vq-49wr-vm6x
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-2026-2320 5.3

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.

Record
PYSEC-2026-2320
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
OSVROOT-APP-PYPI-CVE-2026-27199 5.3

CVE-2026-27199 in rootio-werkzeug - Patched by Root

Root has patched CVE-2026-27199 in the rootio-werkzeug package for Root:PyPI. Multiple fixed versions available.

Record
ROOT-APP-PYPI-CVE-2026-27199
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-2026-1789452203 No score

TuxCare security update for werkzeug (2 CVEs)

TuxCare rebuilt werkzeug to address 2 CVEs. Fixed in 1.0.1.post6+tuxcare.

Record
CLSA-2026-1789452203
Updated
2026-11-02
OSVCLSA-2026-1789452814 No score

TuxCare security update for werkzeug (3 CVEs)

TuxCare rebuilt werkzeug to address 3 CVEs. Fixed in 2.2.3.post5+tuxcare.

Record
CLSA-2026-1789452814
Updated
2026-11-02
OSVCLSA-2026-1789453348 No score

TuxCare security update for werkzeug (4 CVEs)

TuxCare rebuilt werkzeug to address 4 CVEs. Fixed in 2.3.8.post3+tuxcare.

Record
CLSA-2026-1789453348
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
werkzeug
PyPI
 before 3.1.6
3.1.6
py3-werkzeug
Alpine:v3.24
 before 3.1.6-r0
3.1.6-r0
werkzeug
TuxCare:PyPI
From an advisory covering 2 CVEs
 1.0.1 up to 1.0.1.post6+tuxcare, plus listed versions
1.0.1.post1+tuxcare1.0.1.post2+tuxcare1.0.1.post3+tuxcare1.0.1.post4+tuxcare1.0.1.post5+tuxcare
1.0.1.post6+tuxcare
werkzeug
TuxCare:PyPI
From an advisory covering 3 CVEs
 2.2.3 up to 2.2.3.post5+tuxcare, plus listed versions
2.2.3.post1+tuxcare2.2.3.post3+tuxcare2.2.3.post4+tuxcare
2.2.3.post5+tuxcare
werkzeug
TuxCare:PyPI
From an advisory covering 4 CVEs
 2.3.8 up to 2.3.8.post3+tuxcare, plus listed versions
2.3.8.post1+tuxcare2.3.8.post2+tuxcare
2.3.8.post3+tuxcare
werkzeug
PyPI
 before 3.1.6, 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
3.1.6
rootio-werkzeug
Root:PyPI
 before 3.1.5+root.io.1
3.1.5+root.io.1
rootio-Werkzeug
Root:PyPI
 before 3.1.1+root.io.1
3.1.1+root.io.13.1.3+root.io.13.1.1+root.io.23.1.3+root.io.23.1.3+root.io.33.1.1+root.io.33.1.3+root.io.43.1.0+root.io.1
Werkzeug
Root:PyPI
 before 3.1.1+aikido.3
3.1.1+aikido.33.1.3+aikido.4

Public exploits

Links only. Every CVE stores no exploit code.

Public exploits
SourceLinkDate
PoC in GitHubalimezar/CVE-2026-27199-werkzeug-safe-join-bypass-PoC2026-02-20

History

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

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

In short

CVE-2026-27199 is a medium vulnerability (CVSS 6.3) in Pallets Werkzeug, published February 19, 2026. Public exploit code exists. EPSS puts the chance of exploitation in the next 30 days at 0.63%, the 50th percentile. Fixed in werkzeug 3.1.6.

References

This page doesn't list everything

Left out here: 53 versions. The JSON record has them.

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