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Showing posts from September, 2023

.NET in JavaScript, Fake PDF Converter

1. Overview I found a site that distributes curious PDF converter. The executable file distributed at this site appears to be malicious and have several interesting features. ・ .NET Anti-Analysis ・ Execution of external JavaScript payload with WebView2 ・ .NET object manipulation from JavaScript code This post will mention these techniques. The execution flow of this executable is shown below. 2. .NET Anti-Analysis PdfConverters.exe analyzed in this article was created with .NET Core. .NET Core allows developer to embed runtime and libraries into a single executable file. This executable also contains a number of files, which are extracted at execution time into a folder under %TEMP%\PdfConverters. A good way to know the role of these files is to look at [AppName].deps.json. app.deps.json reveals that main functionality of this executable exists in app.dll. [app.deps.json] ... "app/1.0.0": { "dependencies": { "Microsoft.