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.

Profiler 2.3

Profiler 2.3 is out with the following news:

introduced YARA 3.2 support
added groups for logic providers
added Python action to encode/decode text
added Python action to strip XML down to text
added the possibility to choose the fixed font
added color randomization for structs and intervals
added close report and quit APIs
exposed more methods of the Report class (including save)
– improved indentation handling in the script editor
synchronized main and workspace output views
– improved output view
– updated libmagic to 5.21
– updated Capstone to 3.0
– many small improvements
– fixed libmagic on Linux
– removed the tray icon
– minor bug fixes

Logic provider groups

Logic providers can now be grouped in order to avoid clutter in the main window. Adding the following line to an existing logic provider will result in a new group being created:

Encode/decode text action

A handy Python action to convert from hex to text and vice-versa using all of Python’s supported encodings. Place yourself in a hex or text view and run the encoding/decoding action ‘Bytes to text’ or ‘Text to bytes’.

The operation will open a new text or hex view depending if it was an encoding or a decoding.

XML to text action

Strips tags from an XML and displays only the text. The action can be performed both on a hex and text view.

And it will open a new text view. This is useful to view the text of a DOCX or ODT document. In the future the preview for these documents will be made available automatically, but in the meantime this action is helpful.

Fixed font preferences

The fixed font used in most views can now be chosen from the ‘General’ settings.

Struct/intervals color randomization

When adding a structure or interval to the hex view the chosen color is now being randomized every time the dialog shows up. This behaviour can be disabled from the dialog itself and it’s also possible to randomize again the color by clicking on the specific refresh button.

Manually picking a different color for every interval is time consuming and so this feature should speed up raw data analysis.

Report APIs

Most of the report APIs have been exposed (check out the SDK documentation). This combined with the newly introduced ‘quit’ SDK method can be used to perform custom scans programmatically and save the resulting report.

Here’s a small example which can be launched from the command line:

The command line syntax to run this script would be:

The UI will show up and close automatically once the ‘quit’ method is called. Running this script in console mode using the ‘-c’ parameter is not yet possible, because of the differences in message handling on different platforms, but it will be in the future.

Synchronized output views

The output view of the main window and of the workspace are now synchronized, thus avoiding missing important log messages being printed in one or the other context.

Enjoy!

YARA 3.2.0 support

The upcoming 2.3 version of Profiler includes support for the latest YARA engine. This new release is scheduled for the first week of January and it will include YARA on all supported platforms.

One inherent technical advantage of having YARA support in Profiler is that it will be possible to scan for YARA rules inside embedded files/objects, like files in a Zip archive, in a CHM file, in an OLEStream, streams in a PDF, etc.

The YARA engine itself has been compiled with all standard modules (except for cuckoo). Even the magic module is available, since libmagic is also supported by Profiler.

The initial YARA integration comes as a hook extension, an action and Python SDK support. The YARA Python support is the official one and differs from it only in the import statement. You can run existing YARA Python code without modification by using the following import syntax:

So let’s start a YARA scan. To do that, we need to enable the YARA hook extension. On Windows remember to configure Python in case you haven’t yet, since all extensions have been written in it.

When a scan is started, a YARA settings dialog will show up.

This dialog lets us choose various settings including the type of rules to load.

There are four possibilities. A simple text field containing YARA rules, a plain text rules file, a compiled rules file or a custom expression which must eval to a valid Rules object.

The report settings specify how we will be alerted of matches. The ‘only matches’ option makes sure that only files (or their sub-files) with a match will be included in the final report. The ‘add to meta-data” option causes the matches to be visible as meta-data strings of a file. The ‘as threats’ option reports every match as a 100% risk threat. The ‘print to output’ option prints the matches to the output view.

Since we had the ‘only matches’ option enabled, we will find only matching files in our final report.

And since we had also the ‘to meta-data’ option enabled, we will see the matches when opening a file in the workspace.

The YARA scan functionality comes also as an action when we find ourselves in a hex view. You can either scan the whole hex data or select a range. Then press Ctrl+R to run an action and select ‘YARA scan’.

In this case we won’t be given report options, since the only thing which can be performed is to print out matches in the output view.

Like this:

Of course, all supported platforms come also with the official YARA command line utility.

Since this has been a customer request for quite some time, I think it will be appreciated by some of our users.

Stripping symbols from an ELF

Just as the previous post about stripping symbols from a Mach-O binary, here’s one about stripping them from an ELF binary.

The syntax to execute the script is the same as in the previous post, only the called function changes:

Here’s the code:

That’s it!

And here again the complete script which you can use to strip both a Mach-O and an ELF binary.

The Linux x64 version of Profiler should be released soon. So stay tuned!

Stripping symbols from a Mach-O

A common mistake many developers do is to leave names of local symbols inside applications built on OS X. Using the strip utility combined with the compiler visibility flags is, unfortunately, not enough.

So I wrote a small script for Profiler to be run from the command line and I integrated it in the build process.

The syntax to execute the script is:

Here’s the whole code:

The code zeroes names of symbols which are not associated to any section in the binary.

Easy. 🙂

Command-line scripting

The upcoming 2.1 version of Profiler adds support for command-line scripting. This is extremely useful as it enables users to create small (or big) utilities using the SDK and also to integrate those utilities in their existing tool-chain.

The syntax to run a script from command-line is the following:

If we want to run a specific function inside a script, the syntax is:

This calls the function ‘bar’ inside the script ‘foo.py’.

Everything following the script/function is passed on as argument to the script/function itself.

When no function is specified, the arguments can be retrieved from sys.argv.

For the command-line above the output would be:

When a function is specified, the number of arguments are passed on to the function directly:

If you actually try one of these examples, you’ll notice that Profiler will open its main window, focus the output view and you’ll see the output of the Python print functions in there. The reason for this behaviour is that the command-line support also allows us to instrument the UI from command-line. If we want to have a real console behaviour, we must also specify the ‘-c’ parameter. Remember we must specify it before the ‘-r’ one as otherwise it will be consumed as an argument for the script.

However, on Windows you won’t get any output in the console. The reason for that is that on Windows applications can be either console or graphical ones. The type is specified statically in the PE format and the system acts accordingly. There are some dirty tricks which allow to attach to the parent’s console or to allocate a new one, but neither of those are free of glitches. We might come up with a solution for this in the future, but as for now if you need output in console mode on Windows, you’ll have to use another way (e.g. write to file). Of course, you can also use a message box.

But a message box in a console application usually defies the purpose of a console application. Again, this issue affects only Windows.

So, let’s write a small sample utility. Let’s say we want to print out all the import descriptor module names in a PE. Here’s the code:

Running the code above with the following command line:

Produces the following output:

Of course, this is not a very useful utility. But it’s just an example. It’s also possible to create utilities which modify files. There are countless utilities which can be easily written.

Another important part of the command-line support is the capability to register logic providers on the fly. Which means we can force a custom scan logic from the command-line.

This script scans a single file given to it as argument. All callbacks, aside from init, are optional (they default to None).

That’s all! Expect the new release soon along with an additional supported platform. 🙂