Malicious PDF Analysis

In the last few days I have done some analysis on malicious documents, especially PDF. Then I thought, “Why not turn a PDF analysis into an article?”

Let’s go to our case study:

I received a scan request for a PDF file that was reported to support an antivirus vendor, and it replied that the file was not malicious. Because the manufacturer’s analysis was not satisfactory, the team responsible for handling the incident requested a second opinion, since in other anti-virus tools the document was reported to be malicious. The team needed evidence to prove the risk involved in the file.

While conducting an initial analysis on the file, I identified that I had something suspicious:

After an analysis in the structure of objects of the PDF it is possible to identify a malicious URL that is executed during the process of opening the document, that is to say, when the user opens the file in his station it executes of conceal form the call of the URL as shown below :

When performing a domain verification it is possible to reach the IP bound to it:

When performing a URL reputation analysis, a malicious history is identified:

When performing an IP reputation analysis, a malicious history is identified:

The interesting thing is to think that years ago we would never say that infection would be possible through malicious code, URL, shellcode, through obfuscation inside documents like PDF, DOC, DOCx, XLS, XLSx and PPT. Most security tools must always be adapted to this new reality of attack and infection.

It is essential that security professionals are increasingly able to work with this type of analysis that the antivirus tool is not usually able to do, I leave here the hint about the importance of studying malicious document analysis.


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