I think the security checker from Sensio labs is the best approach to this. You can upload your composer file, which is really the list of packages you use and they'll check it against the known reports for various Symfony modules. It's got both the API and its own module with a CLI tool, so you can easily integrate it into monitoring. https://security.sensiolabs.org/

I really wish other projects had something like that (rubygems, pypi, etc.)