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(Potential) Trojan Horse (unicode) characters

Most readers are familiar (enough) with Greek mythology to know about the origin of the Trojan Horse.

Because of the similarities, a particular kind of malware has been named after it, and recently, a second technique to breach security measures, followed.

The idea of this technique is to use (unicode) characters that are not visible/rendered by your IDE, so that you think your code works in a certain way, but the compiler/interpreter will behave differently (as the hacker intended).

So, what kind of characters are we talking about? Which characters can do this nasty trick? All of the following unicode categories are off limits:

• Format
• Surrogate
• Other/not assigned

But - yes there is a but - a lot of alphabets (including Arabic, and Chinese) are marked as “other/not assigned”. To keep things simple I suppose.

Anyhow, if your security concerns are - in this case - limited to .NET (both C# and Visual Basic), I have a solution for you: use these Roslyn Analyzers:

• Qowaiv.Analyzers.CSharp
• Qowaiv.Analyzers.VisualBasic

They will report any violation of this kind as a compiler warning.

Further reading

• https://certitude.consulting/blog/en/invisible-backdoor/
• https://dev.to/dotnetsafer/rip-copy-and-paste-from-stackoverflow-trojan-source-solution-4p8f

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