virtualenv: Deletion recovery can change a symlink target's mode

virtualenv is a tool for creating isolated virtual python environments. Prior to 21.14.9, the safe_delete() deletion error handler responds to a failed removal by reading mode bits with os.lstat(path) and applying owner-write permission with os.chmod(path, ...), which follows a symlink. A planted link inside a read-only directory can therefore cause a victim-owned target outside the destination that is initially not writable by the invoking user to become broadly writable before the retry fails, provided that user owns the target and can change its mode. Another account can use the widened mode only if it can traverse the target's parent directories; root does not reach the demonstrated failure path, and the operation does not itself read the target. This issue is fixed in version 21.14.9.