in-toto vulnerable to Configuration Read From Local Directory

Summary

in-toto is a framework to protect supply chain integrity. The in-toto configuration is read from various directories and allows users to configure the behavior of the framework. The files are from directories following the XDG base directory specification. In versions 1.4.0 and prior, among the files read is `.in_totorc` which is a hidden file in the directory in which in-toto is run. If an attacker controls the inputs to a supply chain step, they can mask their activities by also passing in an `.in_totorc` file that includes the necessary exclude patterns and settings. RC files are widely used in other systems and security issues have been discovered in their implementations as well. Maintainers found in their conversations with in-toto adopters that `in_totorc` is not their preferred way to configure in-toto. As none of the options supported in `in_totorc` is unique, and can be set elsewhere using API parameters or CLI arguments, the maintainers decided to drop support for `in_totorc`. in-toto's `user_settings` module has been dropped altogether in commit 3a21d84f40811b7d191fa7bd17265c1f99599afd. Users may also sandbox functionary code as a security measure.