Sniffing Android apps network traffic

Back in the days, it was really easy to sniff the network traffic made by the Apps in Android. You could do it in a few minutes by adding mitmproxy’s certificate and setting the HTTP proxy on your wifi network settings. That was it. But things have changed (for good) and that’s no longer the case. However, I still want to sniff the network traffic made by the Apps in Android.

How? Well, I can no longer use my smartphone to do it, but I can set up the Android emulator, install the application via the Google Play Store and sniff the network traffic it generates on my PC \o/

Let’s get started. First, install the Android SDK and create an Android virtual device using Android API 30 and x86 architecture (any API and any architecture is fine). However, we need an image without Google Play Store preinstalled as we need a writable /system folder to inject mitmproxy’s certificate later. That’s okay, because we’ll install the Play Store manually.

echo no | ./Android/Sdk/tools/bin/avdmanager create avd -n Pixel_5_API_30 --abi google_apis/x86 --package 'system-images;android-30;google_apis;x86'

Start the virtual device with the additional -writable-system flag which permits us to make /system writable. I also have to unset QT_QPA_PLATFORM=because I’m on wayland and the emulator doesn’t support it.

QT_QPA_PLATFORM= ./Android/Sdk/emulator/emulator @Pixel_5_API_30 -writable-system

Now let’s download the OpenGAPPs that match our API and architecture. Select the pico variant because we don’t need anything else, just the Play Store.

curl -OL 'https://master.dl.sourceforge.net/project/opengapps/x86/20220503/open_gapps-x86-11.0-pico-20220503.zip'

We’ve to decompress it in order to get and push Phonesky.apk to the virtual device. We also need to whitelist its permissions (thank you to the MinMicroGguys).

unzip open_gapps-x86-11.0-pico-20220503.zip
lzip -d Core/vending-x86.tar.lz
tar xf vending-x86.tar
adb root
adb shell avbctl disable-verification # adb disable-verity makes the emulator crash
adb reboot
adb wait-for-device
adb root
adb remount
adb push vending-x86/nodpi/priv-app/Phonesky/Phonesky.apk /system/priv-app/
curl -O https://raw.githubusercontent.com/FriendlyNeighborhoodShane/MinMicroG/master/res/system/etc/permissions/com.android.vending.xml
adb push com.android.vending.xml /system/etc/permissions/

Now, create a dedicated user to run mitmproxy as it’s written in the documentation:

sudo useradd --create-home mitmproxyuser
sudo iptables -t nat -A OUTPUT -p tcp -m owner ! --uid-owner mitmproxyuser --dport 80 -j REDIRECT --to-port 8080
sudo iptables -t nat -A OUTPUT -p tcp -m owner ! --uid-owner mitmproxyuser --dport 443 -j REDIRECT --to-port 8080
sudo -u mitmproxyuser -H bash -c 'mitmproxy --mode transparent --showhost --set block_global=false'

Mandatory copy’n’paste from the mitmproxy documentation page: > Note, as soon as you add the iptables rules, you won’t be able to perform successful network calls until you start mitmproxy.

At this point we are almost there, we just need another step to add the mitmproxy certificate as it’s written in the documentation page:

hashed_name=`sudo openssl x509 -inform PEM -subject_hash_old -in ~mitmproxyuser/.mitmproxy/mitmproxy-ca-cert.cer | head -1`
sudo adb push ~mitmproxyuser/.mitmproxy/mitmproxy-ca-cert.cer /system/etc/security/cacerts/$hashed_name.0
adb shell chmod 664 /system/etc/security/cacerts/$hashed_name.0
adb reboot

You should now have the Play Store, login with your Google account and install the App you need.

That’s it! Happy sniffing!