Breaking Dridex Malware with Excel Macro Password Exploit

[Ronnie] recently posted a new chapter in his adventures in malware deconstruction. This time the culprit was an infected Excel spreadsheet file. The .xls file was attached to a phishing email claiming to be related to a tax rebate. With tax season in full swing, this type of phishing message would be likely to be opened by an inexperienced user.

[Ronnie] saved the file to a virtual machine to prevent his real workstation from getting infected. He then opened it up in Excel and noticed that it immediately attempted to run macros. A macro is essentially visual basic scripting that runs inside of the spreadsheet file. You can use it for simple automation, cell formatting, or do even more complicated tasks like reach out to external websites and pull information. This malware focused on the latter.

[Ronnie] used the alt + F11 shortcut to view the macros. Unfortunately the attackers had password protected them. [Ronnie] wouldn’t be able to view the macro code without knowing the password. Luckily, he learned of a surprisingly simple trick to completely bypass the macro password. He opened up the .xls file in Notepad++ and located three keys; CMG, DPB, and G. [Ronnie] then created and saved a new blank .xls document and password protected the macros with his own password. He opened up this new file in Notepad++ as well, and located those same three keys. He copied the keys from the new file into the old one, and saved the old file. This effectively changed the password of the malware file to the new one he had set for his new file. This is a nifty trick that apparently only works on the older .xls formats, not the newer .xlsx format.

After loading the macros, [Ronnie] quickly noticed that most of the code was obfuscated to make it difficult to analyze. There were, however, three named modules that reference possible sandbox evasion techniques. The malware first invokes these functions to detect the presence of a virtual machine or other type of sandbox. If it detects nothing, then the rest of the malware program is decoded and executed. [Ronnie] removed these checks and then executed the macro to verify that his change had worked.

The next step was to try to view the decoded instructions. The decoded gibberish was saved to a variable. The simplest way for [Ronnie] to view the contents of the variable was to have the program create a pop-up box that displayed the contents of that variable. After making this change and running the program again, he was able to see exactly what the malware was doing. The code actually invoked Powershell, downloaded a file from the Internet, and then extracted and executed that file. In the full write-up, [Ronnie] goes even further by downloading and analyzing the executable.

Decoding ZeuS Malware Disguised as a .DOC

[Ronnie] recently posted about his adventures in decoding malware. One of his users reported a phishy email, which did indeed turn out to contain a nasty attachment. The process that [Ronnie] followed in order to figure out what this malware was trying to do is quite fascinating and worth the full read.

[Ronnie] started out by downloading the .doc attachment in a virtual machine. This would isolate any potential damage to a junk system that could be restored easily. When he tried to open the .doc file, he was presented with an error stating that he did not have either enough memory or disk space to proceed. With 45GB of free space and 2GB of RAM, this should not have been an issue. Something was definitely wrong.

The next step was to open the .doc file in Notepad++ for analysis. [Ronnie] quickly noticed that the file was actually a .rtf disguised as a .doc. [Ronnie] scanned through large chunks of data in an attempt to guess what the malware was trying to do. He noticed that one data chunk ended with the bytes “FF” and D9″, which are also found as the ending two bytes of .gif files.

[Ronnie] copied this data into a new document and removed all new line and return characters. He then converted the hex to ASCII, revealing some more signs that this was actually image data. He saved this file as a .gif and opened it up for viewing. It was a 79KB image of a 3D rendered house. He also found another chunk of data that was the same picture, but 3MB in size. Strange to say the least.

After finding a few other weird bits of data, [Ronnie] finally started to see more interesting sections. First he noticed some strings with mixed up capital and lowercase letters, a tactic sometimes used to avoid antivirus signatures. A bit lower he found a section of data that was about the size of typical shellcode. He decoded this data and found what he was looking for. The shellcode contained a readable URL. The URL pointed to a malicious .exe file that happened to still be available online.

Of course [Ronnie] downloaded the .exe and monitored it to see how it acted. He found that it set a run key in the registry to ensure that it would persist later on. The malware installed itself to the user’s appdata folder and also reached out repeatedly to an IP address known to be affiliated with ZeuS malware. It was a lot of obfuscation, but it was still no match for an experienced malware detective.

Lucid dreaming

When we saw [merkz] use of an Arduino to produce lucid dreaming we were quite shocked. Unlike typical setups that just flash a light through sleep, his system monitors eye movement through electrodes and is able to send the data to a computer for graphing and analyzing.  The only problem being we couldn’t find a circuit diagram or code.

Not ones to be shot down so quickly, a Google revealed this thread on making ‘Dream Goggles’, which was really a Brain-Wave Machine based on the parallel port. Some modifications of an ECG collector’s electrodes using sound cards, and you could have your own lucid dreaming.

[Thanks Phil]