Ethan Furman

When tarfile or zipfile command line interface (CLI) is used to decompress an archive, a Python script shadowing the stdlib can be created. Then if an error occurs during decompressing the next file, the newly created Python script is executed. This is especially true if the created Python is called traceback.py. The problem is that Python adds the current directory to sys.path when python -m MODULE is run, and the archive is also decompressed in the current directory. The fix removes sys.path[0] in gzip, tarfile and zipfile command line interface to prevent shadowing standard library modules from extracted files.

An issue exists where `tarfile.tar filter` can be bypassed using specially crafted link entries, such as symlinks with empty or directory-like names. This allows a malicious archive to redirect subsequent members outside the intended extraction directory, enabling the `tarfile.extractall()` function with `filter="tar"` to write files to arbitrary locations on the system, depending on the permissions of the process performing the extraction.

In the `tarfile` module, the tar and data extraction filters allow the creation of empty directories outside the intended destination on POSIX platforms. This occurs when a member name leaves the destination and subsequently returns to it, such as `../evil/../dest/sub/file`. While the containment check utilizes the resolved path, intermediate directories are created based on the provided name. Member contents remain extracted within the destination. This issue does not affect Windows because `..` components are collapsed before reaching the filesystem.

A defect exists in the CPython “tarfile” module, impacting the “TarFile” extraction and entry enumeration APIs. The tar implementation processes tar archives with negative offsets without error, leading to an infinite loop and deadlock when parsing maliciously crafted tar archives.