Local privilege elevation in Composer-Setup for Windows

Summary

In Composer-Setup for Windows before version 6.0.0, if the developer's computer is shared with other users, a local attacker may be able to exploit the following scenarios. 1. A local regular user may modify the existing `C:\ProgramData\ComposerSetup\bin\composer.bat` in order to get elevated command execution when composer is run by an administrator. 2. A local regular user may create a specially crafted dll in the `C:\ProgramData\ComposerSetup\bin` folder in order to get Local System privileges. See: https://itm4n.github.io/windows-server-netman-dll-hijacking. 3. If the directory of the php.exe selected by the user is not in the system path, it is added without checking that it is admin secured, as per Microsoft guidelines. See: https://msrc-blog.microsoft.com/2018/04/04/triaging-a-dll-planting-vulnerability.