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Improper Handling of Windows Device Names in Werkzeug

CVE-2026-27199

  • Werkzeug
Medium
6.3/10

Summary

Werkzeug is a comprehensive WSGI web application library. In versions through 3.1.5, 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.

  • LOW
  • NETWORK
  • NONE
  • UNCHANGED
  • NONE
  • NONE
  • NONE
  • LOW

CWE-67 - Improper Handling of Windows Device Names

The software constructs pathnames from user input, but it does not handle or incorrectly handles a pathname containing a Windows device name such as AUX or CON. This typically leads to denial of service or an information exposure when the application attempts to process the pathname as a regular file.

References

Advisory Timeline

  • Published