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Added ios & android technique and tool for re-flutter (by @appknox) #2600

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Jun 24, 2024
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Added ios & android technique and tool for re-flutter (by @appknox) #2600

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Added techniques/android/MASTG-TECH-0099.md ,techniques/ios/MASTG-TEC…
sk3l10x1ng Apr 8, 2024
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updated title
sk3l10x1ng Apr 8, 2024
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small correction fixes
sk3l10x1ng Apr 8, 2024
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renamed file to MASTG-TECH-0109.md
sk3l10x1ng Apr 10, 2024
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updated ios & android techniques
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update ios technique
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updated mastg-tech-0109
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updated mastg-tech-0110
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removed duplicate file mastg-tech-0099
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fix typo
cpholguera Apr 27, 2024
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cpholguera Apr 27, 2024
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renamed the android app filename to MASTG-APP-0017
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sk3l10x1ng Jun 18, 2024
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updated TOOL-0101.md
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updated TOOL-0100.md
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sk3l10x1ng committed Apr 17, 2024
commit 3e8026e49d97b488d21cfdac744e6d0a7c9d3954
3 changes: 3 additions & 0 deletions techniques/android/MASTG-TECH-0109.md
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Expand Up @@ -5,6 +5,9 @@ platform: android

Flutter is an open-source UI software development kit (SDK) created by Google. It is used for building natively compiled applications for mobile, web, and desktop from a single codebase. Flutter uses Dart, which is not proxy-aware and uses its own certificate store. The application doesn't take proxy configuration from the system and send the data directly to the server. Due to this, it is not possible to intercept the request using the BurpSuite or any MITM tools.
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Flutter is an open-source UI software development kit (SDK) created by Google. It is used for building natively compiled applications for mobile, web, and desktop from a single codebase. Flutter uses Dart, which is not proxy-aware and uses its own certificate store. The application doesn't take proxy configuration from the system and send the data directly to the server. Due to this, it is not possible to intercept the request using the BurpSuite or any MITM tools.
Flutter is an open-source UI software development kit (SDK) created by Google. It is used for building natively compiled applications for mobile, web, and desktop from a single codebase. Flutter uses Dart, which is not proxy-aware and uses its own certificate store. The application doesn't use the proxy configuration of the system and sends the data directly to the server. Connections are verified against built-in certificates, so any certificates installed on the system are simply ignored. Due to this, it is not possible to intercept HTTPS requests as the certificate of the proxy will never be trusted.

I modified this a bit, since the proxy-unaware isn't really an issue (you could use a VPN, arp spoofing, DNS spoofing, WIFI MITM, ...), but the fact that it has a built-in cert store is an issue that can't be solved by any conventional technique.



There are alternative methods for intercepting traffic, such as [sending traffic to the proxy through ProxyDroid/iptables](https://blog.nviso.eu/2019/08/13/intercepting-traffic-from-android-flutter-applications/). However, these techniques require some configuration. By employing the re-flutter command-line tool, the application can be patched effortlessly without the need for any setup.
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There are alternative methods for intercepting traffic, such as [sending traffic to the proxy through ProxyDroid/iptables](https://blog.nviso.eu/2019/08/13/intercepting-traffic-from-android-flutter-applications/). However, these techniques require some configuration. By employing the re-flutter command-line tool, the application can be patched effortlessly without the need for any setup.
In order to intercept Flutter HTTPS traffic we need to deal with two problems:
* Make sure the traffic is sent to the proxy
* Disable the TLS verification of any HTTPS connection
There are generally two approaches to this: reFlutter and Frida.
* reFlutter: This tool creates a modified version of libFlutter.so which is then repackaged into the APK. It configures the internal libraries to use a specified proxy and disable the TLS verification
* Frida: The [disable-flutter-tls.js script](https://github.com/NVISOsecurity/disable-flutter-tls-verification) can dynamically remove the TLS verification without the need for repackaging. As it doesn't modify the proxy configuration, additional steps are needed (e.g. ProxyDroid, DNS, iptables, ...)

The re-flutter app also has downsides, so this is pretty one-sided:

  • Only works on known/published hashes, otherwise you have to rebuild the engine yourself
  • Repackages the app. This brings complications (e.g. iOS or any app that detects repackaging)

I've used reFlutter a few times (mostly for the object-dump) and it's great when it works, but not straightforward if it doesn't.

So I modified this section to give a more generic introduction of what needs to be done, and then the rest can explain both reFlutter and Frida+(eg)ProxyDroid

We should also use reFlutter, as the tool calls itself, and not re-flutter.


## Intercepting Traffic using re-flutter

1. Patch the app to enable traffic interception.
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3 changes: 1 addition & 2 deletions techniques/ios/MASTG-TECH-0110.md
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Expand Up @@ -5,8 +5,7 @@ platform: ios

Flutter is an open-source UI software development kit (SDK) created by Google. It is used for building natively compiled applications for mobile, web, and desktop from a single codebase. Flutter uses Dart, which is not proxy-aware and uses its own certificate store. The application doesn't take proxy configuration from the system and send the data directly to the server. Due to this, it is not possible to intercept the request using the BurpSuite or any MITM tools.

There are alternative methods for intercepting traffic, such as creating a[WIFI hotspot and utilizing the openvpn approach](https://blog.nviso.eu/2020/06/12/intercepting-flutter-traffic-on-ios/). However, these techniques require some configuration. By employing the re-flutter command-line tool, the application can be patched effortlessly without the need for any setup.

There are alternative methods for intercepting traffic, such as creating a [WIFI hotspot and utilizing the openvpn approach](https://blog.nviso.eu/2020/06/12/intercepting-flutter-traffic-on-ios/). However, these techniques require some configuration. By employing the re-flutter command-line tool, the application can be patched effortlessly without the need for any setup.

## Intercepting Traffic using re-fultter
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