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Werkzeug CVE-2026-21860

MEDIUM
Improper Handling of Windows Device Names (CWE-67)
2026-01-08 security-advisories@github.com GHSA-87hc-h4r5-73f7
Windows Werkzeug Suse Palletsprojects
5.3
CVSS 3.1 · GitHub Advisory
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Vulnerability Assessment

Weakness
CWE
CWE-67
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V5 - File Handling Improper handling of Windows device names
Impact

CVSS 5.3 (MEDIUM). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: None.
Exploit ScenarioDerived

An attacker could exploit this vulnerability to compromise the affected system.
This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

Werkzeug versions prior to 3.1.5 fail to properly validate Windows reserved device names in the safe_join function, allowing attackers to bypass path restrictions by using device names with file extensions or trailing spaces (e.g., CON.txt, AUX ). This denial of service vulnerability affects Windows systems running vulnerable Werkzeug versions and could allow an unauthenticated remote attacker to access restricted files or cause application crashes. A patch is available in version 3.1.5 and later.

Earlier versions of this analysis (1)
v1 Mar 12, 2026 - 21:54 CVSS 5.3

Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.5, Werkzeug's safe_join function allows path segments with Windows device names that have file extensions or trailing spaces. [CVSS 5.3 MEDIUM]

RemediationAI

A vendor patch is available — apply it immediately. Fixed in version 3.1.5.. Restrict network access to the affected service where possible.

Affected Packages

pypi werkzeug fix: 3.1.5

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in pypi

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Technical ContextAI · show details

Affects Werkzeug. Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.5, Werkzeug's safe_join function allows path segments with Windows device names that have file extensions or trailing spaces. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. Windows still accepts them with any file extension, such as CON.txt, or trailing spaces such as CON. This issue has been patched in version 3.1.5.

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  • Exploit and PoC references, threat intelligence from 22 sources
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Severity by source

GitHub Advisory PRIMARY 5.3 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
SUSE MEDIUM

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

Lifecycle Timeline

2
Patch released
Feb 02, 2026 - 17:15 nvd
Patch available
CVE Published
Jan 08, 2026 - 19:15 nvd
MEDIUM 5.3

DescriptionGitHub Advisory

Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.5, Werkzeug's safe_join function allows path segments with Windows device names that have file extensions or trailing spaces. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. Windows still accepts them with any file extension, such as CON.txt, or trailing spaces such as CON. This issue has been patched in version 3.1.5.

Executive ViewAI

Why It Matters

Organizations using Werkzeug should be aware of moderate risk from CVE-2026-21860 rated CVSS 5.3. Exploitation could compromise the security of affected deployments. A patch is available and should be applied during regular vulnerability management.

Business Impact: Low
Compensating Controls

Apply vendor patch. If patching is delayed: restrict network access and enable monitoring.

Threat Intelligence Overview

EPSS Score
0.0%
Top 95% exploitable
Data Quality
4 sources
Confidence: Medium
NVD CVE.org EPSS Vendor GitHub

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact
Low

Priority Score

26
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +26
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Affected Products (CPE)GitHub Advisory

cpe:2.3:a:palletsprojects:werkzeug:*:*:*:*:*:*:*:*

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Same weakness CWE-67 – Improper Handling of Windows Device Names

View all
CVE-2026-17545 MEDIUM
6.9
CVE-2024-35197 MEDIUM
5.4
CVE-2024-51745 LOW
2.3

Vendor StatusVendor

SUSE

Severity: Medium
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 12 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Basesystem 15 SP7 Fixed
SUSE Linux Enterprise Module for Package Hub 15 SP7 Fixed

References

Advisories & patches
PATCH https://github.com/pallets/werkzeug/commit/7ae1d254e04a0c33e241ac1cca4783ce6c875ca3 ADVISORY https://github.com/pallets/werkzeug/security/advisories/GHSA-87hc-h4r5-73f7

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