# CVE-2026-21860: PYSEC-2026-2044 - Werkzeug safe_join() allows Windows special device names with compound extensions

Source: https://junglewise.ai/threats/cve-2026-21860-werkzeug-safe-join-allows-windows-special-device-names-with  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-07  
License: CC BY 4.0 with a link back

CVE-2026-21860 · Severity: low · CVSS 3.1 · Published 2026-07-07

Werkzeug safe_join() allows Windows special device names with compound extensions

Technologies: [werkzeug (PyPI)](https://junglewise.ai/threats/technologies/werkzeug). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-21860 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-21860 being exploited in the wild.

**How severe is CVE-2026-21860?** Low severity, with a CVSS score of 3.1, published 7 July 2026.

**Which products and versions are affected?** werkzeug (PyPI) ECOSYSTEM:introduced=0,fixed=3.1.5.

**Is there a fix for CVE-2026-21860?** Yes. werkzeug (PyPI): upgrade to 3.1.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-21860?** Check whether you run werkzeug (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- werkzeug (PyPI): upgrade to 3.1.5 or later

  ```sh
  pip install "werkzeug>=3.1.5"
  ```


## Affected products

- werkzeug (PyPI) ECOSYSTEM:introduced=0,fixed=3.1.5

## Identifiers

- CVE-2026-21860
- GHSA-87hc-h4r5-73f7
- PYSEC-2026-2044

## Related threats

- [Werkzeug path traversal via NUL device with NTFS ADS marker](https://junglewise.ai/threats/cve-2026-102598-werkzeug-is-a-comprehensive-wsgi-web-application-library-prior)
- [PYSEC-2026-2045 - Werkzeug safe_join not safe on Windows](https://junglewise.ai/threats/cve-2024-49766-werkzeug-safe-join-not-safe-on-windows)
- [PYSEC-2026-2043 - Werkzeug debugger vulnerable to remote execution when interacting with attacker controlled domain](https://junglewise.ai/threats/cve-2024-34069-werkzeug-debugger-remote-code-execution-via-attacker-controlled)
- [PYSEC-2026-1065 - Pallets Werkzeug vulnerable to Path Traversal](https://junglewise.ai/threats/cve-2019-14322-pallets-werkzeug-vulnerable-to-path-traversal)
- [Werkzeug safe_join() allows Windows special device names](https://junglewise.ai/threats/cve-2026-27199-werkzeug-safe-join-allows-windows-special-device-names)