Disassembling toys since '91
Indisputably, Vending Machines are objects of cult. Delicious morsels of Hackers, always. In the beginning they worked offline with coins only, then, NFC- keys/cards models started spreading. If I say “COGES” I’m sure that better times will come to someone’s mind. But… In a bunch of years things changed radically. You distract and a moment after, find the world superseded by things connected to the internet…
One day I decided to interrupt seasoning myself in the bat-cave and direct to my hometown to get some sunlight, so I went to the University to salute an old professor.
“Go to have a coffee!” — he said— and we started chit-chatting while walking through the main corridor.
Me: “let me pay, I have coins!”.
Him: “wait wait! let me use the Vending Machine’s App to pay, the coffee will be cheaper”.
BLE + NFC
Brain: “Mmm… Virtual wallets are cool stuff…”.
Soul: “I dare you to Hack into that!”
~$ White Hat inner voice: “just pats on the shoulder if no bug bounty reward”.
~$ Grey Hat inner voice: “ok, I’ll do that for educational purposes only”.
~$ Black Hat inner voice: “c’mon man, let’s screw that HEAP, great Jupiter!”.
Later in that day…
Needless to say that I picked up my dirty rooted Android smartphone (with USB Debugging Enabled), installed the targeted App from the Play Store and dumped the original *.apk to my laptop via adb.
# adb pull /data/app/com.sitael.vending-1/base.apk ./Argenta.apk
I decompiled the *.apk with apktool
# apktool d ./Argenta.apk -o ./Argenta
and extracted Java sources with jadx
# jadx ./Argenta.apk
Firstly, I made the *.apk debuggable by editing the AndroidManifest.xml file by adding
android:debuggable="true" property to the
Then, I rebuilt the *.apk
# apktool b ./Argenta
created a new key with keytool
# keytool -genkey -v -keystore Argenta.keystore -alias Argenta -keyalg RSA -keysize 2048 -validity 10000
signed the *.apk with jarsigner using the generated key
# jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore Argenta.keystore Argenta.apk Argenta
lastly, I zip-aligned it to make it runnable
# zipalign -v 4 Argenta.apk Argenta-signed.apk
and I installed the final *.apk
# adb install ./Argenta-signed.apk
I ran the App on the smartphone and I started looking at logs with logcat by filtering them via its package name
# adb logcat --pid=`adb shell pidof -s com.sitael.vending`
Nothing special found, so I started to comb through the source codes seeking for juicy information.
Looking better at
AndroidManifest.xml file, I found references to RushOrm
So, first keyword search was
Cool. I booted up the Root Explorer on the phone seeking for
Found. So I pulled it to my laptop with adb
# adb pull /data/data/com.sitael.vending/databases/argenta.db ./
and tried to open it with a DB Browser for SQLite
obviously, it was password protected
Step back to the source codes, looked at
where I found the methods used to configure the database.
My attention was caught by
this.encryptionKey = getDeviceId(context);
I moved to its definition and…
Found that the targeted App used the phone’s IMEI
(*#06#)as encryption key for the SQLite database.
After a couple of seconds of inspection, I opened to the
and edited the
walletCredit field writing changes
then I pushed the database with pumped credit back to the phone
# adb pull ./argenta.db /data/data/com.sitael.vending/databases/argenta.db
In the meantime, while I felt like “Robin Hood” (nostalgic and explicit reference to Age Of Empires cheat code for +1000 gold) I developed an Android utility to quickly dump/restore/tamper the targeted App’s database on the fly.
then I went back to my University again to finally test the Hack
From zero-credit account, I could:
> Inflate the App’s credit.
> Buy stuff.
> Get the remaining credit updated.
> Go back to zero-credit state.
> Inflate the credit again.
> Start over.
With a macro inspection of all the reversed sources I found huge portion of clean code — without obfuscation — that meant no great counter-measures adopted to protect user data and make the App secure at all.
A month ago…
The White Hat inner voice of me picked up the phone and called the company behind this shame to report the vulnerability. I gently suggested them to toss the current architecture and develop a better and secure one from scratch.
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