Extracting C&C from Android Malware

Even though AndroRat (http://www.symantec.com/connect/blogs/remote-access-tool-takes-aim-android-apk-binder) had been around for eons and the source code was made available (https://github.com/DesignativeDave/androrat) but there are many new ones popping out everyday.

Today I will go through with you on how we can make Profiler work extra hard for us.  I will try to fill in required information about where to look out for information and how decode some of the information.

[ 1st Sample used in the analysis ]

MD5: 8BF31084E55D3A83FE6C382986F95C1C
SHA256: DC9A0322CA263D733F91182F1E655A11CBA28DC766031CE0665B6005900450D7

[ Part 1 : Getting Started ]

For those who want to follow along, this is a link to the .apk file. Do note, this is a MALICIOUS file, so please do the analysis in a “safe” environment. The password to the attachment is “infected29A

Now, let’s start getting our hands dirty…and open the suspicious .apk file.  Firstly, we are going to go through the source code and find out what is the important information that we can extract out.

One of the things that malware analyst are interested in is the “Command & Control” of the malware.

As the source code of the malware was made public, we can see where the IP address for the C&C is stored in my/app/client/ProcessCommand.java as shown in the image below.

As Profiler provides SDK for us to analyse DEX and extract relevant Dalvik code, we will be making use of that today by creating “Actions”.  In order to make an action out of it, go to “Extensions” in the main window, then select the Actions tab and click on “Open user plugin directory” as shown below.

[ Scripting the C&C Extraction ]

Create the following file, “androrat.py” in there.  The code for “androrat.py” is shown below:

Next, click on “Open user configuration file” and paste the following:

Save the file, close it. Then click on “Refresh extensions“. You should already see your action among the list.

Now, if you open the .apk file, “double-click” on “classes.dex” and then press “Ctrl+R” you should see your action under the DEX category at the top.

As we can see from the image below after executing the action, you will get the C&C address and port number at the “output” tab as shown below.

The C&C is “http://shoppingapp[.]no-ip[.]biz” and the port number is “81”.

The purpose of this post is to give a better technical understanding of how easy it is to script in Profiler and how malware analysts can easily retrieve important information using static analysis.

The SDK in Profiler gives users the possibility to inspect the code in Dalvik and to extract other important information.

Just by looking at code snippet we showed you, it’s extremely easy for everyone to expand on it and write new utilities.

[ 2nd Sample used in the analysis ]

MD5: 30C385C2928408126F7553134585286E
SHA256: 9E1BEE43A501132DA732D1287126632438B91A9FCBF37AFDA7B8597055960877

The 2nd sample that we will be looking at is OmniRat. The detection rate for OmniRat is just moderate, 20/54 in VT.

The actual piece of malicious code is actually Base64 encoded and hidden away in the resources.asrc file as you can see in the image below

From the image below, we could extract the APK and even inspect it on the fly.
So select the the Base64 encoded string in the resources.asrc file and then press Ctrl+E and click on the filters button on the bottom right.

Now let’s add in 2 filters:
1.) basic/replace in Bytes mode (in: 00 out:) to remove all null bytes
2.) then from_base64 filter.

Now let’s just give it embedded.apk as the filename and add the file as embedded and inspect it.

We can re-apply what we did with the 1st sample using the script which I’ve attached here.

As shown in the image below, the C&C is “strippermona2[.]no-ip[.]info:200”.

We hope you enjoyed reading this and would be happy to receive your feedback!

Malware in a MSG

Even though sending malware via zipped attachments in spam emails is nothing new and had been around for eons but many people are still puzzled at how it works. Thus, I will go through with you on how to do it with Profiler. I will try to fill in required information about where to look out for information and how decode some of the information.

Firstly, we are going to learn how are a bit about the .msg file format and how is it used to store a message object in a .msg file, which then can be shared between clients or message stores that use the file system.

From an investigator’s point of view, you should always analyze the .msg file without installing Outlook. In order to analyze the .msg file without Outlook, we can read more about the file format from:

  • http://download.microsoft.com/download/5/D/D/5DD33FDF-91F5-496D-9884-0A0B0EE698BB/[MS-OXMSG].pdf
  • https://msdn.microsoft.com/en-us/library/cc463912(v=exchg.80).aspx
  • http://www.fileformat.info/format/outlookmsg/

The purpose of this post is to give a better technical understanding of how attackers makes use spam emails to spread malware.

[ Sample used in the analysis ]
MD5: BC1DF9947B9CF27B2A826E3B68C897B4
SHA256: C7AC39F8240268099EC49A3A4FF76174A50F1906BBB40AE6F88425AF303A44BB
Sample: Sample

[ Part 1 : Getting Started ]
For those who want to follow along, this is a link to the .msg file. Do note, this is a MALICIOUS file, so please do the analysis in a “safe” environment. The password to the attachment is “infected29A

Now, let’s start getting our hands dirty…and open the suspicious .msg file.

The msg file is already flagged by Profiler, as it contains some suspicious features.
Each “__substg” contains valuable pieces of information. The first four of the eight digits at the end tells you what kind of information it is (Property). The last four digits tells you the type (binary, ascii, Unicode, etc)

  • 0x007d: Message header
  • 0x0C1A: Sender name
  • 0x0C1F: Sender email
  • 0x0E1D: Subject (normalized)
  • 0x1000: Message body

[ Part 2 : Email investigation ]
If we are interested in email investigation, let’s check out the following file, “__substg1.0_0C1F001F”.

As we can see below, the sender’s email address is “QuinnMuriel64997@haarboutique-np.nl
But is it really sent from Netherlands?

Well, let’s check out the message header located in “__substg1.0_007D001F” to verify that.

If we were to do through the message header, do a whois on “haarboutique-np.nl” and check out the MX server. We can confirm that the sender is spoofing email as well.

From the message header, we can conclude that the sender sent the email from “115.78.135.85” as shown in the image and the extracted message header as shown below.

    Received: from [115.78.135.85] ([115.78.135.85])
    by mta02.dkim.jp (8.14.4/8.13.8) with ESMTP id u44L8X41032666
    for <info@dkim.jp>; Thu, 5 May 2016 06:08:35 +0900

Whois information showed that IP address where this spam email is sent from is from Vietnam.
But it doesn’t mean that the attacker is from Vietnam. Anyone in the world can buy web hosting services in Vietnam. This is just to let you know that the attacker is definitely not sending from “haarboutique-np.nl

[ Part 3 : Email investigation ]
Using this information opening the “__substg1.0_0E1D001F” file and we can see the subject, “Re:

Hmmmm…this doesn’t look any useful at all. Let’s try opening the file, “__substg1.0_1000001F”, containing the “subject body” instead.

      “Hi, info

Please find attached document you requested. The attached file is your account balance and transactions history.

Regards,
Muriel Quinn”

Awesome, Muriel Quinn is sending me my account balance and transactions history which I may or may not have requested at all. Awesome, he is also attaching the files to the email just for me. This is definitely suspicious to me.

[ Part 4 : Email attachment ]
Now that we are interested in the attachments, let’s look at “Root Entry/__attach_version1.0_#00000000” and refer to the specifications again.

  • //Attachments (37xx):
  • 0x3701: Attachment data
  • 0x3703: Attach extension
  • 0x3704: Attach filename
  • 0x3707: Attach long filenm
  • 0x370E: Attach mime tag

If we were to look at “__substg1.0_3704001F”, we will see that the filename of the attachment is called “transa~1.zip” and the display name “__substg1.0_3001001F” of the attachment is called “transactions-625.zip”.

Now let’s look at the actual data located within “__substg1.0_37010102” as shown below.

Now, let’s press “Ctrl+A” to select the entire contents. Then copy it into a new file as shown in the image below.

But as we can see on the left, Profiler can identify what is inside the attachment. There are 3 Javascript files inside the .zip file.

Now let’s fire up “New Text View” and copy the contents of “transactions 774219.js” as shown below.

Press “Ctrl+R” and select “Beautify JavaScript” and Profiler will “JSBeautify” it for you. But let’s add some “Colouring” to it by doing “Right-click -> Language -> JavaScript” as shown below.

We can use Profiler to debug the JavaScript but I shall leave that as an exercise for the readers.
The decoded JavaScript will look something like this.

As we can see from the image above, it is downloading from “http://infograffo[.]com[.]br/lkdd9ikfds” and saving it as “ew3FbUdAB.exe” in the victims’ TEMP directory.

We won’t be going through on reversing the malware.

In the meantime, we hope you enjoyed reading this and would be happy to receive your feedback!

PDF/XDP Malware Reversing

Recently version 2.6 of Profiler has been released and among the improvements support for XDP has been introduced. For those of you who are unfamiliar with XPD, here’s the Wikipedia description:

“XML Data Package (XDP) is an XML file format created by Adobe Systems in 2003. It is intended to be an XML-based companion to PDF. It allows PDF content and/or Adobe XML Forms Architecture (XFA) resources to be packaged within an XML container.

XDP is XML 1.0 compliant. The XDP may be a standalone document or it may in turn be carried inside a PDF document.

XDP provides a mechanism for packaging form components within a surrounding XML container. An XDP can also package a PDF file, along with XML form and template data. When the XFA (XML Forms Architecture) grammars used for an XFA form are moved from one application to another, they must be packaged as an XML Data Package.”

So I’ll use the occasion to show the reversing of a nice PDF with all the goodies. Let’s open the suspicious PDF.

The PDF is already heavily flagged by Profiler, as it contains many suspicious features.

If we take a look, just out of curiosity, at the object 8 of the PDF we will notice that the XDP data contains a bogus endstream keyword to fool the parsers of security solutions.

Profiler handles this correctly, so we don’t have to do anything, just worth mentioning.

Let’s take a look at the raw XDP data.

As you can see, it is completely unreadable because of the XML escaped characters. Even this is not really important for us, since the XML parser of Profiler handles this automatically, again just worth mentioning.

So let’s open directly the embedded XDP child and we can see a readable and nicely indented XML.

We can see that the XML contains JavaScript code, but Profiler already warns us of this. So let’s just click on the warning.

The code isn’t readable. So let’s select the JavaScript portion and then press Ctrl+R->Beautify JavaScript.

Much better, isn’t it?

The code is quite easy to understand although it’s obfuscated. It takes a value straight from the XDP, processes it and then calls eval on it.

This is the value it takes:

What we want is the result of the processing, before eval is called. So what I did is to modify slightly the JavaScript code like this:

I didn’t paste now the entire value in here as it was way too big, but I did so in the code edit:

At this point, we can just press Ctrl+R->Debug/Execute JavaScript and get the result of the execution.

We will get the following code:

What it does is basically to spray the heap using an array. It changes the payload based on the version of Adobe Reader. The version is retrieved by calling the _l5 function.

Now we could just examine the _l1 or _l2 payloads directly, but just to make sure I let the code generate a spray portion. So I changed the code accordingly and avoided to actually spray a lot of data.

We can run this script in the JavaScript debugger (Ctrl+R->Debug JavaScript).

The final print will give us the payload in memory. We can copy the just the initial part, avoiding the padding. Let’s paste the string into a text editor in Profiler and then Ctrl+R->Hex string to bytes.

If we look at the payload, we can see that the beginning (the marked portion) looks like ROP code. So in order to avoid looking for the gadgets in memory, let’s skip the ROP as it most likely is only going to jump to the actual shellcode. Let’s assume that is the case and thus focus on the data which follows.

We can see a web address at the end of the data. So we could just assume that the shellcode downloads an executable and runs it. But just for the sake of completeness, let’s analyze it.

We can of course disassemble the shellcode by applying a filter to it (Ctrl+T->x86 disasm). But what we’ll do is to use a debugger via Ctrl+R->Shellcode to execute. This way we can quickly step through what it does.

Here’s the commented code:

So yes, in the end it just downloads the file from the address we’ve seen and tries to execute it, then tries to register it as a COM object. Some AV-evasion techniques are also present.

Cheers!

Profiler 2.6

Profiler 2.6 is out with the following news:

– added initial support for XML files
– added support for XDP files (extraction of embedded PDFs)
– exposed the ABC format
– improved the parsing of malformed PDF streams
– fixed the code signing on OS X to meet El Capitan requirements
– fixed the JS debugger on Linux
– various bug fixes and improvements

Enjoy!

Windows Memory Forensics

Let’s begin with an image:

Yep. That’s an icon. In an executable. In a process address space. In a raw memory dump.

And here is the video demonstration:

This is just a proof-of-concept. We still haven’t decided whether to develop this further. It really depends on whether the forensic community is interested in having such a product. So, even a re-tweet will have an impact on our decision. 🙂 We wanted to show what is currently possible and, of course, it’s not the end of the cool things which are possible.

In case we decide to go ahead with the development, we will probably create a beta-test group of potential customers and decide with them a roadmap for a 1.0 version, taking into consideration all those features which are essential to them. What we already support are the Windows versions that go from XP to 10 on the following architectures: x86, x86-PAE, x64. And, of course, the software itself, just like Profiler, runs on Windows, OS X and Linux.

And now to the more technical side if you’re interested. What we have shown in this demonstration is just a Python extension for Profiler. To be more specific, it’s only about 1000 lines of Python code and this includes all the UI views. The bulk of the work went into exposing all the necessary capabilities of our SDK to Python. Of course, all this work also benefits other extensions, not just the memory forensics ones. So, if this project ends with this post, it’s really not a tragedy, as we haven’t lost any significant time developing specific stuff for it.

So why did we choose to write our memory forensics support in Python, rather than in C++, which would’ve taken us a lot less time? The reasons are several. The memory forensic field is always changing rapidly and setting code in stone by compiling it wouldn’t be a good idea. Also, we wanted to give our customers the possibility to inspect the code and to modify it. Just by looking at existing code it’s extremely easy to write new utilities. While on the other hand, having our core engine and UI written in C++, makes our tool very fast. We think this is the perfect combination.

If you’re wondering why we didn’t use Volatility as a backbone, the answer is that it would’ve been incompatible on a licensing level and way too difficult to fit nicely into our existing framework to accomplish what we wanted to do.

We hope you enjoyed the demo and we would be happy to receive your feedback!

Profiler 2.5

Profiler 2.5 is out with the following news:

introduced scan provider extensions
added support for Torrent files
added the capability to display views as dialogs
exposed official Python bindings for capstone
– added new controls to custom views
– updated capstone to 3.0.3
fixed failed allocation security issue
– various bug fixes and improvements

Dialogs from views

In this new edition it’s possible to create dialogs out of views. Just like this:

Of course, it doesn’t have to be a custom view, it can even be a simple text view or a hex view, although usually custom views make more sense for a dialog, as you’ll probably want to show some standard buttons like “Ok” and “Cancel” at the bottom.

Capstone bindings

While Capstone has been part of Profiler for quite some time now, now it’s possible to directly call its official Python bindings. The module can be found under ‘Pro.capstone’ and can be imported easily to be made working with existing code:

Failed allocation security issue

In the Qt framework memory allocations fail silently, at least in the release version. We didn’t notice it, because in the debug version they would at least throw an exception preventing further execution. Since in release the execution wouldn’t be stopped, it was in some cases possible to trigger a failed allocation and then make the program use memory it didn’t own (so basically a buffer overflow). This problem has now been fixed.

Credit goes to the Insid3Code Team for having found and reported the issue.

Enjoy!

Torrent Support

Following our recent introduction to Scan Providers, here’s a first implementation example. In this post we’ll see how to add support for Torrent files in Profiler. Of course, the implementation shown in this post will be available in the upcoming 2.5.0 release.

Let’s start by creating an entry in the configuration file:

For the automatic signature recognition we may rely on a simple one:

Torrent files are encoded dictionaries and they usually start with the announce item. There’s no guarantee for that, but for now this simple matching should be good enough.

The encoded dictionary is in the Beconde format. Fortunately, someone already wrote the Python code to decode it:

We can now load the file and decode its dictionary:

We call the GetDictionary method first time in the _initObject method, so that the parsing occurs when we’re in another thread and we don’t stall the UI.

Let’s display the parsed dictionary to the user:

Dictionary

This is the description extracted from Wikipedia of some of the keys:

  • announce—the URL of the tracker
  • info—this maps to a dictionary whose keys are dependent on whether one or more files are being shared:
    • name—suggested filename where the file is to be saved (if one file)/suggested directory name where the files are to be saved (if multiple files)
    • piece length—number of bytes per piece. This is commonly 28 KiB = 256 KiB = 262,144 B.
    • pieces—a hash list, i.e., a concatenation of each piece’s SHA-1 hash. As SHA-1 returns a 160-bit hash, pieces will be a string whose length is a multiple of 160-bits.
    • length—size of the file in bytes (only when one file is being shared)
    • files—a list of dictionaries each corresponding to a file (only when multiple files are being shared). Each dictionary has the following keys:
      • path—a list of strings corresponding to subdirectory names, the last of which is the actual file name
      • length—size of the file in bytes.

While the dictionary already could suffice to extract all the information the user needs, we may want to present parts of the dictionary in an easier way to read.

First, we’d like to show to the user some meta-data information, which may be contained in the dictionary. To do that, we add a meta-data scan entry:

We also warn the user if the file exceeds the allowed maximum. We perform the whole scan logic in the UI thread, since we’re not doing any CPU intensive operation and thus we return SCAN_RESULT_FINISHED, which causes the _threadScan method not be called.

Here we return the meta-data to the UI:

MetaData

Also it would be convenient to see the list of trackers and files. Let’s start with the trackers:

Trackers

When retrieving data from the dictionary, we also make sure that it is in the correct type, so that the code which handles this data won’t end up generating an exception when trying to process an unexpected type.

And now the files:

Files

And that’s it. Now again the whole code for a better overview:

We could still extract more information from the torrent file. For instance, we could show the list of hashes and to which portion of which file they belong to. If that’s interesting for forensic purposes, we can easily add this view in the future.

Scan Providers

Version 2.5.0 is close to being released and comes with the last type of extension exposed to Python: scan providers. Scan providers extensions are not only the most complex type of extensions, but also the most powerful ones as they allow to add support for new file formats entirely from Python!

This feature required exposing a lot more of the SDK to Python and can’t be completely discussed in one post. This post is going to introduce the topic, while future posts will show real life examples.

Let’s start from the list of Python scan providers under Extensions -> Scan providers:

Scan provider extensions

This list is retrieved from the configuration file ‘scanp.cfg’. Here’s an example entry:

The name of the section has two purposes: it specifies the name of the format being supported (in this case ‘TEST’) and also the name of the extension, which automatically is associated to that format (in this case ‘.test’, case insensitive). The hard limit for format names is 9 characters for now, this may change in the future if more are needed. The label is the description. The ext parameter is optional and specifies additional extensions to be associated to the format. group specifies the type of file which is being supported; available groups are: img, video, audio, doc, font, exe, manexe, arch, db, sys, cert, script. file specifies the Python source file and allocator the function which returns a new instance of the scan provider class.

Let’s start with the allocator:

It just returns a new instance of TestScanProvider, which is a class dervided from ScanProvider:

Every scan provider has some mandatory methods it must override, let’s begin with the first ones:

_clear gives a chance to free internal resources when they’re no longer used. In Python this is not usually important as member objects will automatically be freed when their reference count reaches zero.

_getObject must return the internal instance of the object being parsed. This must return an instance of a CFFObject derived class.

_initObject creates the object instance and loads the data stream into it. In the sample above we assume it being successful. Otherwise, we would have to return SCAN_RESULT_ERROR. This method is not called by the main thread, so that it doesn’t block the UI during long parse operations.

Let’s take a look at the TestObject class:

This is a minimalistic implementation of a CFFObject derived class. Usually it should contain at least an override of the CustomLoad method, which gives the opportunity to fail when the data stream is first loaded through the Load method. SetDefaultEndianness wouldn’t even be necessary, as every object defaults to little endian by default. SetObjectFormatName, on the other hand, is very important, as it sets the internal format name of the object.

Let’s now take a look at how we scan a file:

The code above will issue a single warning concerning native code. When _startScan returns SCAN_RESULT_OK, _threadScan will be called from a thread other than the main UI one. The logic behind this is that _startScan is actually called from the main thread and if the scan of the file doesn’t require complex operations, like in the case above, then the method could return SCAN_RESULT_FINISHED and then _threadScan won’t be called at all. During a threaded scan, an abort by the user can be detected via the isAborted method.

From the UI side point of view, when a scan entry is clicked in summary, the scan provider is supposed to return UI information.

This will display a text field with a predefined content when the user clicks the scan entry in the summary. This is fairly easy, but what happens when we have several entries of the same type and need to differentiate between them? There’s where the data member of ScanEntryData plays a role, this is a string which will be included in the report xml and passed again back to _scanViewData as an xml node.

For instance:

Becomes this in the final XML report:

The dnode argument of _scanViewData points to the ‘d’ node and its first child will be the ‘o’ node we passed. the xml argument represents an instance of the NTXml class, which can be used to retrieve the children of the dnode.

But this is only half of the story: some of the scan entries may represent embedded files (category SEC_File), in which case the _scanViewData method must return the data representing the file.

Apart from scan entries, we may also want the user to explore the format of the file. To do that we must return a tree representing the structure of our file:

The enableIDs method must be called right after creating a new FormatTree class. The code above creates a format item with id 1 with a child item with id 2, which results in the following:

Format tree

But of course, we haven’t specified neither labels nor different icons in the function above. This information is retrieved for each item when required through the following method:

The various items are identified by their id, which was specified during the creation of the tree.

The UI data for each item is retrieved through the _formatViewData method:

This will display a custom view with a table and a hex view separated by a splitter:

Custom view

Of course, also have specified the callback for our custom view:

It is good to remember that format item IDs and IDs used in custom views are used to encode bookmark jumps. So if they change, saved bookmark jumps become invalid.

And here again the whole code for a better overview:

If you have noticed from the screen-shot above, the analysed file is called ‘a.t’ and as such doesn’t automatically associate to our ‘test’ format. So how does it associate anyway?

Clearly Profiler doesn’t rely on extensions alone to identify the format of a file. For external scan providers a signature mechanism based on YARA has been introduced. In the config directory of the user, you can create a file named ‘yara.plain’ and insert your identification rules in it, e.g.:

This rule will identify the format as ‘test’ if the first 4 bytes of the file match the string ‘test’: the name of the rule identifies the format.

The file ‘yara.plain’ will be compiled to the binary ‘yara.rules’ file at the first run. In order to refresh ‘yara.rules’, you must delete it.

One important thing to remember is that a rule isn’t matched against an entire file, but only against the first 512 bytes.

Of course, our provider behaves 100% like all other providers and can be used to load embedded files:

Embedded files

Our new provider is used automatically when an embedded file is identified as matching our format.

Profiler 2.4

Profiler 2.4 is out with the following news:

added initial support for PDB files (including export of types)
added support for Windows Encoded Scripts (VBE, JSE)
– introduced fixed xml structures
added automatic string decoding in struct tables
added Python string command line execution
– remember the last selected logic group
– fixed missing support for wchar_t in C types
– updated Qt to 5.4.1
– various bug fixes

While the most important newly introduced feature is the support for PDB files, here are some interesting new features:

Support for Windows Encoded Scripts (VBE, JSE)

Windows encoded scripts like VBE and JSE files (the encoded variants of VBS and JS script files) are now supported and automatically decoded.

In the screen-shot you can see the decoded output of an encoded file (showed at the bottom).

Automatic string decoding in struct tables

A very basic feature: byte-arrays in structures are automatically checked for strings and in case decoded.

(notice the section name automatically displayed as ascii string)

Python string command line execution

Apart from executing script files passed as command line arguments, now it is also possible to execute Python statements directly passed as argument.

For instance:

The optional argument ‘-c’ specifies to not display the UI.

Enjoy!

PDB support (including export of types)

The main feature of the upcoming 2.4 version of Profiler is the initial support for the PDB format. Our code doesn’t rely on the Microsoft DIA SDK and thus works also on OS X and Linux.

Since the PDB format is undocumented, this task would’ve been extremely difficult without the fantastic work on PDBs of the never too much revered Sven B. Schreiber.

Let’s open a PDB file.

As you can see the streams in the PDB can be explored. The TPI stream (the one describing types) offers further inspection.

All the types contained in the PDB can be exported to a Profiler header by pressing Ctrl+R and executing the ‘Dump types to header’ action.

Now the types can be used from both the hex editor and the Python SDK.

We can explore the dumped header by using, as usual, the Header Manager tool.

The type showed above in the hex editor is simple. So let’s look what a more complex PDB type may look like.

The PDB code is also exposed to the SDK. This is a small snippet of code, which dumps all the types to a text buffer and then displays them in a text view.

In order to dump all types to a single header, you can use the DumpAllToHeader method.