A .csproj file is an XML-based project file used by C# and .NET tools to describe how a project should build. It typically defines source files, references, target framework, compiler options, and imported build logic such as .props or .targets files. In practice, it is part of the instructions that tell the build system what to compile and how to package the result.
Because .csproj files influence the build process, they are security-sensitive. If an attacker can edit a project file, they may be able to change compilation behavior, add unexpected dependencies, or trigger malicious build steps that run during normal development. Defenders should treat these files as trusted build inputs: review changes carefully, restrict write access, monitor for unusual imports or commands, and verify the integrity of release artifacts. In supply-chain attacks, the project file itself can become a delivery path, not just the code it builds.