By Tomer Bitton, security researcher, Imperva
PDFs are widely used business file format, which makes them a common target for malware attacks. Because PDFs have so many "features," hackers have learned how to hide attacks deep under the surface. By using a number of utilities, we are able to reverse engineer the techniques in malicious PDFs, providing insight that we can ultimately use to better protect our systems. We'll take you through the process that a hacker uses to insert a piece of malware into a sample PDF.
By opening the PDF file with a text editor it is possible to see that there are some encrypted objects. The first circle, object 11, is a command to execute Javascript in object 12. The second and third circles, are a command for object 12 to filter the Javascript with AsciiHexDecode. The main reason for this filter is to hide malicious code inside the PDF and avoid anti-virus detection. This is our first red flag.
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