Forensic Blogs

An aggregator for digital forensics blogs

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April 1st 2020: FlashPix File With VBA Code

Last year, there was some misunderstanding regarding Office Documents with VBA code mistakenly identified as FlashPix picture files.

The FlashPix picture format is an old format, based on the Compound File Binary Format (what I like to call OLE files). It has no support for VBA code at all (it doesn’t support any embedded scripting).

However, since it is an ole file, it’s technically possible to add storages and streams containing VBA code. This code can never execute, because the FlashPix specifications does not support it, and hence there are no image viewers that would recognize and execute this code.

So I took a FlashPix image (3d996a887c4a1b5b5ce70528f6bb4508). Here you can see the streams it contains:

And then I took a malicious AutoCAD drawing, and copied the VBA streams and storages into the FlashPix file:

Giving me this file 5040ef90824371a0bd0acaa36263553b.When I submitted this file to VirusTotal a couple of months ago, the AV detection ratio was 29/59. Which is far better than the other “AV-alert pictures” that I created.

If you are in need of a benign file that will trigger anti-virus, I shared this FlashPix PoC on the new malware sharing service Malware Bazaar.

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Update: msoffcrypto-crack.py Version 0.0.5

This new version of msoffcrypto-crack.py, a tool to crack encrypted MS Office documents, comes with a new option to generated a password dictionary based on the filename of the document.

Option -p allows the user to provide a dictionary file. Use value #f to generate a dictionary based on the filename: This will generate a dictionary of all possible substrings of the filename.

I had to analyze an encrypted spreadsheet yesterday, and the password was in the name, like this:

msoffcrypto-crack_V0_0_5.zip (https)
MD5: 1514DA367DCFF7051AB117266CE65BD3
SHA256: FEEFDD89134083EA19936494C8FCBD05804B3B9C0D4C5FBAFE06578D466B50AE

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mimikatz Is My New EICAR

I helped a friend creating picture files to be detected by anti-virus. They are not malicious: they don’t execute code neither trigger a vulnerability.

The EICAR test file is detected by many anti-virus programs, except when it is appended to arbitrary files (this is according to specs).

Starting with a one-pixel JPEG and PNG file, I append the EICAR test file. And with a JPEG file, I can also insert the EICAR file as a comment:

The detection scores on VirusTotal show that these files are not detected by many anti-virus programs:

JPEG + EICAR: 6/55 PNG + EICAR: 7/58 JPEG + EICAR comment: 2/57

That wasn’t good enough for my friend, she needed something with a higher detection score.

Since several years now, there is a Windows program that triggers many anti-virus programs: mimikatz.

When I try mimikatz with picture files, I get better detection scores than for the EICAR test file (as I expected):

JPEG + MIMIMATZ.EXE: 19/58 PNG + MIMIMATZ.EXE: 15/57 JPEG + MIMIMATZ.DLL: 12/57

 

And I have a picture file with even higher detection scores, but you’ll have to wait until April Fools day for the details 😉 .