Security implications of open CoreCLR (CoreRun.exe)
Completed on 05-Feb-2016 (26 days) -- Updated on 23-Nov-2016

Some of the conclusions of this project aren't applicable anymore.
To know more about all this, read "OVER-8-MONTH-LATER UPDATE" in the Open .NET & CoreCLR section.

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Introduction >
Compilation & CoreRun.exe

As already explained in the first section and in various parts of the previous project, the quality of the code in CoreCLR (but also in CoreFX & Roslyn) is certainly high: good and clear structure, efficient algorithms, helpful comments, etc. Any experienced .NET programmer should be able to start working with it almost immediately. On the other hand, compiling a more or less relevant portion of the code is a different story.

Note that the .NET Framework is a huge and very complex project which has been systematically improved during the last quite a few years by a relevant number of different people; only this issue should be enough to not expect it to be immediately adapted to a so relevant change like "suddenly" becoming open source. But there is still another issue, the ultimate responsible for having created this project, which is much more relevant here: the bipartition underlying the whole .NET Framework and what it implies. That is, only part of the information required by a .NET executable is contained in the file itself; the remaining bits are taken from the .NET libraries present in the given computer (e.g., automatically installed with Windows). The CoreCLR repository includes the source code of some of these libraries (the most basic ones) and that's why validating the compilation outputs isn't easy. How telling the aforementioned executable to rely on the .NET libraries generated by the last compilation?

Building and using a new version of the CoreCLR libraries requires from a not-too-simple multi-step process which is explained in detail in the corresponding documentation. One of the outputs of this process is the file CoreRun.exe, which answers the aforementioned question (how telling the executable...?) and represents the main reason for having started this project. Basically speaking, CoreRun.exe allows to directly modify the pure essence of any .NET executable (i.e., telling it to rely on a modified version of some basic libraries) and this project analyses whether this fact represents a real security threat.