Virtualenv versions prior to 1.6.2 and 1.18.1_2 have a file permission issue where files copied from a cached app-data directory retain their original permissions, potentially allowing wider access than intended. This occurs because shutil.copy preserves cached file modes regardless of the current umask, leading to files with overly permissive modes in new environments. An attacker with access to the new environment and the ability to traverse it can exploit this to modify files such as pip/__init__.py, which then run with the environment owner's privileges.