In This section we want to change the value of inputs and outputs in native library functions. It should be clear for you that we can’t just simply change the function arguments and return value because they may have different class types. For example if you want to change the input of a function that is
jstring
you can’t provide a JavaScript string.Frida is awesome. It provide bridge between Frida to Java. Therefore we can create any Java class and Objects. You can access them with
Java.vm.getEnv()
. Also to see full abilities you have you can check there:
As you see we can create
jstring
by using newStringUtf
. Example:
Interceptor.attach( Module.findExportByName("libnativesecret.so", "Java_lab_seczone64_nativesecret_MainActivity_encryptDecrypt"), {
onEnter: (args) => {
args[2] = Java.vm.getEnv().newStringUtf("Seczone64")
},
onLeave: (ret) => {
ret.replace(Java.vm.getEnv().newStringUtf("Hooora. We did it. :)"))
}
})
}
You can’t directly change return value. You should use
.replace
function to change it.If you need C/C++ string type look at here:
