CODEWITHSUNDEEP
javaandroidmobilefrida
wqhd_
wqhd_

Reputation: 31

Iterate over a list in Frida

I am trying to figure out how to read a public unmodifiableList field of a Java class with Frida. Here is the class I have:

public final class MyClass {
   public final String myString;
   public final List myList;

   public MyClass() {
       this.myString = "Hello!";
       this.myList = Collections.unmodifiableList({ "this_is_a_string" });
   }
}

and here is the JS Frida code I am using to extract the two fields:

Java.perform(function() {
    function onField(instance) {
        const fields = instance.getClass().getDeclaredFields();
        for(var i = 0; i < fields.length; i++) {
            const value = fields[i].get(instance);
            if(fields[i].getName() == "myString") {
                // This correctly prints "Hello!".
                console.log("myString: " + value);
            } else if(fields[i].getName() == "myList") {
                for(var j = 0; j < value.length; i++) {
                    // This prints out a blank line, as opposed to "this_is_a_string".
                    console.log(value[j]);
                }
            }
        }
    }
    Java.choose("com.myapp.MyClass", { onField: onField, onComplete: function() {} })
});

The problem is that I cannot access any methods or fields of the unmodifiableList (size() and indexing included.). How can I read from this list?

Upvotes: 0

Views: 1905

Answers (1)

wqhd_
wqhd_

Reputation: 31

The problem was solved with the usage of Java.cast.

// ...
var list = Java.cast(value, Java.use("java.util.List"));

Upvotes: 3

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