File Extension ASPX
File extension ASPX is used to denote files containing ASP.NET source code to be run on a web server (server-side scripts). This can be written in any of the languages supported by the .NET framework such as C#, and can range from simple web scripts to full-blown web service applications or rich internet applications. These ASPX scripts are usually developed within an Integrated Development Environment (IDE) such as Microsoft Visual Studio .NET, although they can be viewed and modified in any text editor as the code is written in plain text and is not compiled to machine code.
When a file with the ASPX extension is requested from a web server, the server will parse and execute the code, returning the results to the web browser for the user to view. This means the user of a web application does not get to see the underlying code of the application, only the results of running it. This is usually an (X)HTML page generated by the program containing the results of a database query or dynamically created images, for example.
As with any other web scripting or programming language, care must be taken when writing ASP .NET applications to avoid vulnerabilities that involve user input, especially where database queries are involved. There have been several well-known security issues where servers have become vulnerable due to badly written scripts, and this also works the other way round. Software vulnerabilities in the web browser software used to view web pages have often been exploited by utilising specially written scripts using ASP.NET or PHP for example. Although many vulnerabilities are fixed quickly upon discovery, there are nevertheless always risks associated with running code from untrusted sources so care should still be taken when browsing the internet or when writing server-side scripts.