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03 May, 2009

Dissecting iMobile - Security Analysis of ICICI Mobile Banking App

ICICI Bank’s iMobile website has some of the worst server side validations ever, which is what prompted me to download the mobile app’s JAR file, study it in detail and write this post. According to the website, until the Reserve Bank of India comes out with mobile banking guidelines and approves it, mobile banking is supposed to be halted. Technically, it means that, all existing users shouldn’t be able to use the service what-so-ever and new user signups should be prevented & a notification stating that they should retry later should be shown.

Therefore, in this scenario, I shouldn’t have been able to download the app to my mobile device. The website of ICICI fails in not enforcing this by providing the following ways:
Existing users who have already installed the app are given an option to ‘Upgrade’ from within the mobile app itself. This opens up a webpage in the phone’s native browser, whose URL is http://mobile.icicibank.com/upgrade?version=null.
The actual iMobile website has some stupid javascript validation, which is very easy to bypass using modern browsers. Heck, just by browsing the HTML source code of the page, you will be able to easily find the URL for the application JAR files. Put 2 and 2 together and you will be able to download the app.

Which brings me to explain Step 2 in detail:
On any browser, go to View->Source. This will display the source code of the rendered HTML page. Notice the first It contains many functions & the most important functions to us are “submitForm” and “displayOption”. The line of interest in submitForm method is document.jump1.action="https://infinity.icicibank.co.in/web/apps/"+fileName;. That line pretty much gives away everything. All you have to do is, navigate to the above mentioned URL and append a filename to it for download.

What filename do you have to give and How?
That’s where our displayOption function is very useful. That function contains a set of simple If-Else conditional statements, which have the respective filenames. For e.g. if you want to download “M20P1520ALL1.jar”, then just append it to the URL & access it using the address bar. Therefore, the URL becomes https://infinity.icicibank.co.in/web/apps/M20P1520ALL1.jar Being a JAR file, most browsers will display a “Save As” dialog box. Now, just download the file and transfer it to your mobile. The application is fairly straight forward.

Where ICICI Bank failed?
They should have disabled the link mentioned in #1 above and replaced it with some text that says, “RBI mobile banking guidelines blah blah…”. But some clever users will bookmark the link to the JAR file and try to access the JAR file by bypassing the link itself. When they do that, the web server should return a “404 - Resource Not Found” error. Got it? Implementing this is pretty simple.
There shouldn’t have been such a lot of useless javascript on the page. Firstly, they should have removed the device selection drop down box. Secondly, they should have replaced this page with an alternative. Thirdly, this mobile banking link should have been removed in the home page itself. Fourthly, they should have validated on the server for JAR file downloads and should have displayed the “404 - Resource Not Found” error page.
Ok. Leave aside #1 and #2. At least the mobile app should have thrown soft errors when users try to access mobile banking from the JavaME app. Any bank would store all activity data for a certain period of time. So when you access the bank’s service from a mobile device, the server software surely knows about it, which means, the server software should have returned errors to the user instead of allowing the user to do transactions.
There’s one more bug in the app itself. When you launch the app, it will prompt you to sync the data on the device to its servers for faster access the next time. When you click “OK” to synchronize, it will wait for a few minutes and show a message as, “There is no data to synchronize”. When you proceed further and try to access your info, it will again prompt you to sync the data. That’s frustrating. Either you should sync the data properly or you should access the server every time over a secure channel. As simple as that. That’s not followed too.
For me, all these things imply only thing. ICICI wants the existing users to continue using the app, thereby disobeying RBI’s orders or they are having some really bad programmers who don’t know the stuff they are doing. At a time when people fear about Google tracking their internet usage, this is MY/YOUR FINANCIAL INFORMATION, which is at risk Right?

That was a long post already We still have some more to go. Lets take a break.

Image Credits

Back? Ok Now, lets dissect the actual JAR file and look into the technical details of its implementation.

The Manifest File:
Rename the .JAR extension to .ZIP extension and extract it to your favourite folder. Open the “META-INF” folder and open the “MANIFEST.MF” file in a text editor. As you will note, it contains lots of very valuable information, especially the socket URLs of various mobile service providers. User agent is also very interesting. When sending HTTP requests through the application, it uses that property for setting the “user-agent” HTTP header. They also have debug strings enabled, which means by snoping around using a good file manager for your mobile, you will be able to get technical errors! thereby, letting us know how the app works itself, what requests it sends, its behaviour etc.

Another important item is, “MIDlet-Name” property in the manifest. This property determines what name the user sees after he installs the app on his mobile. Using the same name, when future upgrades are made available, the app is just replaced in place of the old one, which means, if you modify the “MIDlet-Name” property and install the app again, you will have 2 copies of the same app. THIS SHOULD NEVER BE ALLOWED FOR A HIGHLY CRITICAL FINANCIAL APPLICATION. Isn’t it? As an example, try changing the MIDlet-Name of the Yahoo! Go JAR file and try to install the app again on your mobile. My E51 shows an “Invalid JAR” error message because of MD5 sum checks etc.

Some more Holes:
Now, move back to the folder where the JAR file has been extracted. It contains a bunch of .class files. Pass it through a decompiler. You will get “perfect” java source code files. The code looks obfuscated. But its not obfuscated enough. Anybody will be able to make good sense from the source code. All the URLs, all the used strings and everything else will be clearly visible. By using the app on your mobile side-by-side, you will be easily able to go through the source code. All in all, I wouldn’t use this app anymore until the security measures are tighter.

What should the bank do here?
Shouldn’t allow the installation of 2 apps of the same JAR with different names. Take this example of the Yahoo! Go JAR file.
I guess these mobile providers’ socket URLs are used for a one time basis to send verification SMS. If that be the case, they shouldn’t be present in the manifest file for a variety of reasons that I won’t discuss here.
There’s an interesting property named “WSCDomainName” in the manifest file. I guess it expands to “Web Service Client Domain Name”, though I’m not sure about it. Suggestion: Encrypt the name value pairs.
Most importantly, sign the application using the Java Signed program. C’mon, users are doing financial transactions and a signed app will increase their confidence of using this application.

Suggestion for Users:
Users should install these kinds of apps on their mobile’s inbuilt memory, instead of the memory card. That is, when you connect your phone to the PC in thumb drive mode, all the RMS file stores for the mobile app are clearly visible. There are many decoders available on the internet that can read content from the RMS file stores. When you store this app on your mobile’s inbuilt memory, you can’t read those stores directly and there are a number of checks in place, that prevent reading it.

Thats about it !

Of course, this blog post can’t be termed as a full fledged security analysis. But most of what has been ignored by the bank are mere basics. They must have more secure systems in place.

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