Read more on the blog: https://swarm.ptsecurity.com/fork-bomb-for-flutter/
This framework helps with Flutter apps reverse engineering using the patched version of the Flutter library which is already compiled and ready for app repacking. This library has snapshot deserialization process modified to allow you perform dynamic analysis in a convenient way.
Key features:
socket.cc
is patched for traffic monitoring and interception;dart.cc
is modified to print classes, functions and some fields;- display absolute code offset for functions
- contains minor changes for successfull compilation;
- if you would like to implement your own patches, manual Flutter code changes are supported using a specially crafted
Dockerfile
- Android: arm64, arm32;
- iOS: arm64;
- Release: Stable, Beta
# Linux, Windows, MacOS
pip3 install reflutter==0.7.8
impact@f:~$ reflutter main.apk
Please enter your Burp Suite IP: <input_ip>
SnapshotHash: 8ee4ef7a67df9845fba331734198a953
The resulting apk file: ./release.RE.apk
Please sign the apk file
Configure Burp Suite proxy server to listen on *:8083
Proxy Tab -> Options -> Proxy Listeners -> Edit -> Binding Tab
Then enable invisible proxying in Request Handling Tab
Support Invisible Proxying -> true
impact@f:~$ reflutter main.ipa
You need to specify the IP of your Burp Suite Proxy Server located in the same network where the device with the flutter application is. Next, you should configure the Proxy in BurpSuite -> Listener Proxy -> Options tab
- Add port:
8083
- Bind to address:
All interfaces
- Request handling: Support invisible proxying =
True
You don't need to install any certificates. On an Android device, you don't need root access as well. reFlutter also allows to bypass some of the flutter certificate pinning implementations.
The resulting apk must be aligned and signed. I use uber-apk-signer
java -jar uber-apk-signer.jar --allowResign -a release.RE.apk
.
To see which code is loaded through DartVM, you need to run the application on the device. Note that you must manually find what _kDartIsolateSnapshotInstructions
(ex. 0xB000 ) equals to using a binary search. reFlutter writes the dump to the root folder of the application and sets 777
permissions to the file and folder. You can pull the file with adb command
impact@f:~$ adb -d shell "cat /data/data/<PACKAGE_NAME>/dump.dart" > dump.dart
file contents
Library:'package:anyapp/navigation/DeepLinkImpl.dart' Class: Navigation extends Object {
String* DeepUrl = anyapp://evil.com/ ;
Function 'Navigation.': constructor. (dynamic, dynamic, dynamic, dynamic) => NavigationInteractor {
Code Offset: _kDartIsolateSnapshotInstructions 0x0000000000009270
}
Function 'initDeepLinkHandle':. (dynamic) => Future<void>* {
Code Offset: _kDartIsolateSnapshotInstructions 0x0000000000412fe8
}
Function '_navigateDeepLink@547106886':. (dynamic, dynamic, {dynamic navigator}) => void {
Code Offset: _kDartIsolateSnapshotInstructions 0x0000000000002638
}
}
Library:'package:anyapp/auth/navigation/AuthAccount.dart' Class: AuthAccount extends Account {
PlainNotificationToken* _instance = sentinel;
Function 'getAuthToken':. (dynamic, dynamic, dynamic, dynamic) => Future<AccessToken*>* {
Code Offset: _kDartIsolateSnapshotInstructions 0x00000000003ee548
}
Function 'checkEmail':. (dynamic, dynamic) => Future<bool*>* {
Code Offset: _kDartIsolateSnapshotInstructions 0x0000000000448a08
}
Function 'validateRestoreCode':. (dynamic, dynamic, dynamic) => Future<bool*>* {
Code Offset: _kDartIsolateSnapshotInstructions 0x0000000000412c34
}
Function 'sendSmsRestorePassword':. (dynamic, dynamic) => Future<bool*>* {
Code Offset: _kDartIsolateSnapshotInstructions 0x00000000003efb88
}
}
Use the IPA file created after the execution of reflutter main.ipa
command. To see which code is loaded through DartVM, you need to run the application on the device. reFlutter will print the dump file path to the Xcode console logs with the reFlutter tag
Current working dir: /private/var/mobile/Containers/Data/Application/<UUID>/dump.dart
Next, you will need to pull the file from the device
The resulting offset from the dump can be used in the frida script
frida -U -f <package> -l frida.js --no-pause
To get value for _kDartIsolateSnapshotInstructions
you can use readelf -Ws libapp.so
Where is the value you need in the Value
field
- Display absolute code offset for functions;
- Extract more strings and fields;
- Add socket patch;
- Extend engine support to Debug using Fork and Github Actions;
- Improve detection of
App.framework
andlibapp.so
inside zip archive
The engines are built using reFlutter in Github Actions to build the desired version, commits and snapshot hashes are used from this table.
The hash of the snapshot is extracted from storage.googleapis.com/flutter_infra_release/flutter/<hash>/android-arm64-release/linux-x64.zip
If you would like to implement your own patches, manual Flutter code change is supported using specially crafted Docker
git clone https://github.com/Impact-I/reFlutter && cd reFlutter
docker build -t reflutter -f Dockerfile .
Build command:
docker run -it -v "$(pwd):/t" -e HASH_PATCH=<Snapshot_Hash> -e COMMIT=<Engine_commit> reflutter
Example:
docker run -it -v "$(pwd):/t" -e HASH_PATCH=aa64af18e7d086041ac127cc4bc50c5e -e COMMIT=d44b5a94c976fbb65815374f61ab5392a220b084 reflutter
EXAMPLE BUILD ANDROID ARM64: docker run -e WAIT=300 -e x64=0 -e arm=0 -e HASH_PATCH=<Snapshot_Hash> -e COMMIT=<Engine_commit> --rm -iv${PWD}:/t reflutter
FLAGS: -e x64=0 <disables building for x64 architecture, use to reduce building time> -e arm64=0 <disables building for arm64 architecture, use to reduce building time> -e arm=0 <disables building for arm32 architecture, use to reduce building time> -e WAIT=300 -e HASH_PATCH=[Snapshot_Hash] -e COMMIT=[Engine_commit] <here you specify commit for your engine version, take it from enginehash.csv table or from flutter/engine repo>