Threat Level: green Handler on Duty: Xavier Mertens

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Analyzing TNEF files

Yesterday I came across a file type I rarely have to analyze: "Transport Neutral Encapsulation Format". It's an attachment file format used by Outlook and Exchange.

Here is how the file command identifies it:

There are different free and opensource programs and libraries that can parse this file format. There's a Python module tnefparse that comes with a parsing program:

So this TNEF file contains one attached file: an .iso file.
tnefparse can extract this .iso file:

I've covered the analysis of .iso files before in this diary entry.

With 7-zip, I can look into the .iso file:

And extract the .exe (MD5 d71e537c1ca1aba1f6854c0cb7b71835) file:

Didier Stevens
Microsoft MVP Consumer Security


560 Posts
ISC Handler
Dec 31st 2017

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