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Learning CodeQL

If you tried the Github Secure Code Game I blogged about before, you got a first introduction on code scanning with CodeQL. In this post I want to share some other resources that can help you to get a deeper understanding in what CodeQL is and how it can help you to find security vulnerabilities in your code.

What is CodeQL?

CodeQL is a static analysis tool that can scan your code for vulnerabilities. CodeQL lets you query code as though it were data. By writing queries you can find  variants of a vulnerability.

Remark: CodeQL is free for research and open source.

How to run CodeQL?

The easiest way to try out CodeQL is by enabling the code scanning with CodeQL GitHub Action on a repository. Behind the scenes this will create a CodeQL database. This database is a relational representation of the code base, which contains information about the different source code elements, such as classes and functions, and puts each of those into a separate table of data. Each language has its own database schema, but generally there is a table for classes, a table for functions and so on, and relationships between these tables. For most programming languages CodeQL standard libraries provide wrappers and layers around that database schema.

A second option is to setup a local CodeQL database using the CodeQL command line tool. The easiest way to install the CodeQL CLI locally is as an extension to the gh CLI tool—GitHub’s official CLI tool.

The CodeQL CLI allows you to download an already created database (for a popular existing open source project) or you can create a new database yourself(which can take some time).

To create a new database use the following command:

codeql database create sqli-db --language csharp

I typically use the CodeQL plugin for Visual Studio Code. 



There you can directly download the database (if available) or select the database you have just created:



Now we can right click on a CodeQL file and choose ‘CodeQL: Run query on selected database’:



Running the query can take some time(it is possible to run the query on a set of files instead of the whole database), but once the query has completed you can browse through the results:



Learn more

If you want to learn more, I can recommend the following resources:

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