rthooks: secure temp directories used by matplotlib and win32com rthooks #7827
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The run-time hooks that relocate the package's configuration/cache directory into isolated temporary directory create this directory using the `tempfile.mkdtemp` function. According to its documentation, the function creates the temporary directory "in the most secure manner possible", and the created directory should be "readable, writable, and searchable only by the creating user ID". However, this does not apply to Windows, where the 0o700 POSIX permissions mask passed to the underyling `os.mkdir` call has no effect. Consequently, the access to the created temporary directory is in fact gated only by the access to the parent directory. So as long as `TEMP` and `TMP` point to `%LOCALAPPDATA%\Temp`, the created temporary directories are typically inaccessible to other users, who do not have access to the user's home directory. On the other hand, if the temporary directory base is relocated to a system-wide location (e.g., `c:\temp`), the temporary directories created by the run-time hooks might become accessible to other users as well. A malicious user with local access might thus modify the contents of the temporary directory, interfering with the application. If the application is running in privileged mode and developer mode is enabled on the system, they might also attempt a symlink attack due to lack of hardened mode for `shutil.rmtree` (used for clean up) on Windows. Therefore, we replace the use of `tempfile.mkdtemp` with custom function that uses original `mkdtemp` on POSIX and provides a Windows-specific implementation that secures the access to created directory via security descriptor passed to the `CreateDirectoryW` call. This is a `ctypes`-based port of the code that we already have in bootloader for mitigating the same issue with temporary directory in onefile builds. In order to share the implementation among the two run-time hooks that require it, the code is provided by a new `_pyi_rth_utils` PyInstaller "fake" package, which is bundled with the frozen application on demand (i.e., if it is referenced in any of collected run-time hooks).
bwoodsend
approved these changes
Aug 7, 2023
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The run-time hooks that relocate the package's configuration/cache directory into isolated temporary directory create this directory using the
tempfile.mkdtempfunction. According to its documentation, the function creates the temporary directory "in the most secure manner possible", and the created directory should be "readable, writable, and searchable only by the creating user ID".However, this does not apply to Windows, where the 0o700 POSIX permissions mask passed to the underyling
os.mkdircall has no effect. Consequently, the access to the created temporary directory is in fact gated only by the access to the parent directory. So as long asTEMPandTMPpoint to%LOCALAPPDATA%\Temp, the created temporary directories are typically inaccessible to other users, who do not have access to the user's home directory. On the other hand, if the temporary directory base is relocated to a system-wide location (e.g.,c:\temp), the temporary directories created by the run-time hooks might become accessible to other users as well. A malicious user with local access might thus modify the contents of the temporary directory, interfering with the application. If the application is running in privileged mode and developer mode is enabled on the system, they might also attempt a symlink attack due to lack of hardened mode forshutil.rmtree(used for clean up) on Windows.Therefore, we replace the use of
tempfile.mkdtempwith custom function that uses originalmkdtempon POSIX and provides a Windows-specific implementation that secures the access to created directory via security descriptor passed to theCreateDirectoryWcall. This is actypes-based port of the code that we already have in bootloader for mitigating the same issue with temporary directory in onefile builds.In order to share the implementation among the two run-time hooks that require it, the code is provided by a new
_pyi_rth_utilsPyInstaller "fake" package, which is bundled with the frozen application on demand (i.e., if it is referenced in any of collected run-time hooks).