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Inspecting Phone Network Connections

Mitmproxy setup (for macbook):

  1. If not already installed, install Homebrew, see https://brew.sh/. Use:
  • /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
  1. Install mitmproxy, see https://mitmproxy.org/. Use:
  • brew install mitmproxy
  1. Setup macbook as wireless AP:
  • Connect macbook to one end of a wired ethernet cable (you'll need a usb-to-ethernet adapter for this) and connect other end of ethernet cable to an internet gateway e.g. your home router. This will be used to connect the macbook to the internet.
  • Open Settings, go to Sharing and click on "Internet Sharing".
  • In the "Share your connect from" drop down box select the wired ethernet connection.
  • In the "To computers using" box choose Wi-Fi.
  • Click start. You should see the Wifi icon in the top bar of the macbook change to be grayed out. Your macbook is now acting as a WiFi access point. Devices connecting to it will have their traffic routed over the wired ethernet cable connected to the macbook. The name of the Wifi network will be the same as the name of the macbook, on your phone open settings, look for the available Wifi networks and connect to the macbook.
  1. Setup transparent proxying using mitmproxy, see https://docs.mitmproxy.org/stable/howto-transparent/ for details. In summary:

rdr on bridge100 inet proto tcp to any port {80,443} -> 127.0.0.1 port 8080 block drop quick on bridge100 inet proto udp to any port 443

  • Setup the firewall to redirect Wifi traffic to mitmdump using: sudo pfctl -f pf.conf; sudo pfctl -e

  • Edit file /etc/sudoers and add line:

ALL ALL=NOPASSWD: /sbin/pfctl -s state

  • Type mitmproxy to start up mitmproxy for the first time, then exit. This will create folder ~/.mitmproxy that contains the CA cert used by mitmproxy

  • Update the permissions using chmod a+r ~/.mitmproxy/mitmproxy-ca.pem

  • Now type sudo -u nobody mitmdump --mode transparent --showhost --ssl-insecure --rawtcp to startup mitmproxy. Traffic from the phone will now be routed to mitmproxy. Typically you'll see errors as the phone detects the presence of mitmproxy intercepting connections.

Mitmproxy setup (Raspberry Pi)

  1. A Raspberry Pi is fine for running mitmproxy too, and much cheaper than a Macbook! But best to use a newer Raspberry Pi 4 as I've had trouble trying to use an older Pi 3. To set it up, first follow the instructions to configure Pi as a Wifi router.

  2. Install mitmproxy using apt-get install mitmproxy. Setup the firewall rules to redirect traffic to mitmproxy by running this shell script.

  3. Run mitmproxy using e.g. mitmdump --mode transparent --showhost --ssl-insecure --rawtcp

Install mitmproxy CA cert as trusted on phone

The next step is to install the CA cert of mitmproxy as a trusted cert on the phone.

iPhone

  1. Go to Settings-WiFi and connect to laptop access point
  2. Open Safari and navigate to url http://mitm.it (note, http not https). Click "Get mitmproxy-ca-cert.pem" for iOS. You'll see a message asking "This website is trying to download a configuration profile. Do you want to allow this?", choose "Allow".
  3. Go to Settings-General-Profile, you should see mitmproxy, click on it and choose "install".
  4. Go to Settings-General-About and at bottom of page choose "Certificate Trust Settings". You should see mitmproxy, click the toggle to enable full trust
  5. As a test, go back to Safari and navigate to https://leith.ie/nothingtosee.html. You should see connections being logged by mitmdump on the laptop as you type the URL, and then the actual connection to leith.ie/nothingtosee.html. You may still see a few connections reporting errors, but mostly the connections should be accepted now - the connections that fail are being made by system processes, not Safari, and we need to use Cydia Substrate to make them work with mitmdump.

Android

To install a trusted (or system) CA cert on Android requires rooting the phone.

  1. Root your phone - typically this involves unlocking the bootloader (often the hardest task!), then using fastboot to install TWRP recovery and then sideloading Magisk to patch the system boot image. The details of rooting are phone dependent, but you want to get to a setup where you have access to a rooted adb shell and have Magisk installed.

  2. Create a file with the mitmproxy CA cert in Android compatible format by:

  3. Edit the shell scripts cacert_setup.sh and cacert.sh to use the your cert filename (i.e. edit the c8750f0d.0 entries to match the output from the openssl command you used above).

  4. Once you have your phone rooted, connect the phone to a laptop by usb cable and on the laptop type the following commands to copy files from your laptop to the phone:

    • adb push cacert* /data/local/tmp/
    • adb push c8750f0d.0 /data/local/tmp/
  5. Now open an adb shell by typing adb shell.

  6. In the adb shell type su to get root access and type the following commands:

    • chmod a+x cacert*
    • cp cacert.sh /data/adb/service.d/
    • ./cacert_setup.sh
    • What are these commands doing? Files in folder /data/adb/service.d/ are executed by Magisk on startup, so placing cacert.sh causes the mitmproxy CA cert to one setup automatically after a restart of the phone (otherwise its wiped). On Android 10 and later the /system folder is mounted as readonly and this cannot be changed, so the scripts mount an writeable overlay at /system/etc/security/cacerts/, copy the existing system certs into that together with the mitmproxy cert and then set the permissions and selinux labels to the appropriate values.
    • You can check that the mitmproxy cert has been successfully installed by looking at Settings-Security-Encryptions and credentials-Trusred Credentials on the phone - that lists the trusted CA certs and mitmproxy should be listed there if things worked ok.
    • Note: installing the mitmproxy cert as a system cert is enough to allow the traffic generated by Google Play Services etc to be decrypted by mitmproxy, but other apps may include additional pinning of SSL certs. Those need to be treated on a case by case basis, and typically require use of a custom Frida script to bypass the checks.

iPhone Cydia Substrate setup:

To bypass SSL cert checks made by iPhone system processes its necessary to jailbreak the phone.

  1. Download Checkra1n from https://checkra.in/, install and follow instructions to jailbreak iPhone.
  2. Once phone has rebooted, connect phone to a Wifi network (a normal network, not the mitmproxy one), open checkra1n app and choose option to install Cydia. A Cydia app icon will appear on the iphone desktop.
  3. Now click on the Cydia icon to open the Cydia app and: (i) Install Cydia substrate: on tabs at bottom of screen click "search", then search for "substrate". You should find "Substrate Safe Mode", install this and click Respring button. (ii) Optional: install frida, see https://frida.re/docs/ios/
  4. Install custom ssl unpinning package:
  • Open Cydia app.
  • Click on "sources" tab at bottom, then click "Edit" and "Add". Enter https://doug-leith.github.io/cydia/ as new source.
  • Click on new source, the on "Tweaks" and install the "unpin" package. Note: source code for unpin package is at https://github.com/doug-leith/cydia
  • We need to restart all of the system processes in order to activate the unpin package. To do that, with phone connected by usb cable to macbook, run Checkra1n again.
  • Once the phone has rebooted, change the settings to connect to the mitmproxy access point. You should now see all connections being successfully decoded by mitmproxy (you may see some warning messages warning about self-signed certs (these are Apple certs) but the --ssl-insecure option to mitmdump allows these to pass).

Notes:

  1. With phone jailbroken using Checkra1n, to access the iPhone from the command line over usb use:
  • brew install libimobiledevice

to install libimobiledevice package. See https://libimobiledevice.org/ for details. 2. Once libimobiledevice is installed, to ssh into phone over usb use:

iproxy 2222 44 &

ssh root@localhost -p 2222

The password in "alpine". To copy files off of phone use:

  • scp -3 scp://root@localhost:2222//<file> .
  1. Once libimobiledevice is installed, to get device details use:
  • ideviceinfo

Huawei Setup

Rooting a Huawei handset is more involved than for other handsets since Huawei no longer officially support bootloader unlocking. Extra steps are also needed to unpin SSL cert checks made by system processes. See here for more details

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Cydia repository with just one package (to bypass SSL cert checks on iOS)

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