Local Privilege Escalation in Windows

Impact

A PyInstaller built application, elevated as a privileged process, may be tricked by an unprivileged attacker into deleting files the unprivileged user does not otherwise have access to.

A user is affected if all the following are satisfied:

• The user runs an application containing either matplotlib or win32com.
• The application is ran as administrator (or at least a user with higher privileges than the attacker).
• The user’s temporary directory is not locked to that specific user (most likely due to TMP/TEMP environment variables pointing to an unprotected, arbitrary, non default location).
• Either:
  • The attacker is able to very carefully time the replacement of a temporary file with a symlink. This switch must occur exactly between shutil.rmtree()'s builtin symlink check and the deletion itself
  • The application was built with Python 3.7.x or earlier which has no protection against Directory Junctions links

Patches

The vulnerability has been addressed in https://github.com/pyinstaller/pyinstaller/pull/7827 which corresponds to pyinstaller >= 5.13.1

Workarounds

Is there a way for users to fix or remediate the vulnerability without upgrading?

No workaround, although the attack complexity becomes much higher if the application is built with Python >= 3.8.0.