JS – Cerbero Blog

We have already shown in the past how simple it is to leverage the capabilities of Cerbero SDK to extract JavaScript from PDF documents using a simple hook.

In this post we’ll use a package to deploy the demo code.

The advantage of using an installable package is that it minimizes the effort on the part of the user to test the code and the deployment method is compatible with both Cerbero Suite and Cerbero Engine.

We explained how packages work in a previous post in case you missed that.

The demo code is the following:

from Pro.Core import *

def printJSEntry(sp, xml, tnode):
    # data node
    dnode = xml.findChild(tnode, "d")
    if not dnode:
        return
    # we let Cerbero extract the JavaScript for us
    params = NTStringVariantHash()
    params.insert("op", "js")
    idnode = xml.findChild(dnode, "id")
    if idnode:
        params.insert("id", int(xml.value(idnode), 16))
    ridnode = xml.findChild(dnode, "rid")
    if idnode:
        params.insert("rid", int(xml.value(ridnode), 16))
    js = sp.customOperation(params)
    # print out the JavaScript
    print("JS CODE")
    print("-------")
    print(js)

def pdfExtractJS(sp, ud):
    xml = sp.getReportXML()
    # object node
    onode = xml.findChild(None, "o")
    if onode:
        # scan node
        snode = xml.findChild(onode, "s")
        if snode:
            # enumerate scan entries
            tchild = xml.firstChild(snode)
            while tchild:
                if xml.name(tchild) == "t":
                    # type attribute
                    tattr = xml.findAttribute(tchild, "t")
                    # check if it's a JavaScript entry
                    if tattr and int(xml.value(tattr)) == CT_JavaScript:
                        printJSEntry(sp, xml, tchild)
                tchild = xml.nextSibling(tchild)

And the configuration for the hook extension is the following:

[PDF JavaScript Extraction Demo]
file = pdf_js_extract_demo.py
scanned = pdfExtractJS
formats = PDF
enable = yes

Out of this two parts we created a package with an automatic setup which you can download from here.

The package can be installed with a few clicks. In fact, on Windows it can be installed directly from the shell context menu.

The setup dialog informs you that the package is verified as it was signed by Cerbero. Do not install the package if the signature couldn’t be verified!

The package once installed is visible in the list of installed packages. From there it can be uninstalled.

While the package is installed, it will print out the JavaScript code contained in PDF documents even if such documents are encrypted.

Packages are a not only a great way to deploy tools and plugins for Cerbero Suite and Cerbero Engine, but they also enable the secure deployment of demonstration snippets and other data.

The upcoming 0.9.5 version of the Profiler introduces tools to interactively analyze JavaScript code. In a few words it adds the capability to execute snippets of code or to debug them. The JavaScript engine used is the one in WebKit.

Let’s take a look at the newly introduced actions:

The ‘Execute JavaScript‘ action executes a script and lets the user decided whether to process ‘eval‘ calls or not.

Even when ‘eval‘ calls are not being processed, the argument is still printed out for the user to inspect. And in case ‘eval‘s are performed, then the result (if any) is printed out as well.

js_eval: print('hello world'); 1 + 1
js_print: hello world
js_eval_result: 2

Let’s take a look at the same code under the JavaScript debugger. Given the JavaScript debug capabilities already in Qt, it was easy to integrate a full fledged debugger:

The debugger can be executed as a stand-alone utility (jsdbg.exe) as well.

It shouldn’t take long before the new version is ready and then we’ll see these features in action against some real world samples. Stay tuned!

Tag: JS

PDF JavaScript Extraction Demo Package

JavaScript Analysis