Thanks for converting this into a work item. This issue becomes a real serious problems in Enterprise Scale applications of NuGet where builds are supposed to be referencing only "golden components". In such scenarios it is unacceptable for a developer to sneak in a NuGet.exe with a custom config file and enable dowlnloads from a repository not considered golden.

The extensibility of MSBuild actually leads to a situation where any pre-build script might be used to create a nuget.config file at runtime with an untrusted source and force fetch from unsupported repositories. For enterprise level applications it is a necessity to suppress all repositories other than a golden one on certain build servers.

We would welcome a pull request for this issue that implements a design akin to how web.config handles this.

http://msdn.microsoft.com/en-us/library/system.configuration.sectioninformation.inheritinchildapplications.aspx

Elements could specify that the setting cannot be overridden or augmented in other web.config files.

I can give this a go but work is manic these days and I really would not be able to commit on a date. I am actually new to this kind of thing. Would you mind stating some of the obvious with respect to initiating this pull, committing to deadlines and submitting code changes?

@nikrox, please take a look at http://docs.nuget.org/docs/contribute/contributing-to-nuget. This has guidance on how to submit a pull request.