The --export-marks option of git fast-import is exposed also via the in-stream command feature export-marks=... and it allows overwriting arbitrary paths.When submodules are cloned recursively, under certain circumstances Git could be fooled into using the same Git directory twice. We now require the directory to be empty.Incorrect quoting of command-line arguments allowed remote code execution during a recursive clone in conjunction with SSH URLs. While the only permitted drive letters for physical drives on Windows are letters of the US-English alphabet, this restriction does not apply to virtual drives assigned viah subst :. Git mistook such paths for relative paths, allowing writing outside of the worktree while cloning. Git was unaware of NTFS Alternate Data Streams, allowing files inside the .git/ directory to be overwritten during a clone.When running Git in the Windows Subsystem for Linux while accessing a working directory on a regular Windows drive, none of the NTFS protections were active. Filenames on Linux/Unix can contain backslashes. On Windows, backslashes are directory separators. Git did not use to refuse to write out tracked files with such filenames.Recursive clones are currently affected by a vulnerability that is caused by too-lax validation of submodule names, allowing very targeted attacks via remote code execution in recursive clones.