Frida Tutorial 3

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This is a summary of the post: https://joshspicer.com/android-frida-1 APK: https://github.com/OWASP/owasp-mstg/blob/master/Crackmes/Android/Level_01/UnCrackable-Level1.apk

Solution 1

Based in https://joshspicer.com/android-frida-1

_exit() 함수를 후킹하고 복호화 함수를 사용하여 verify를 누를 때 플래그를 frida 콘솔에 출력하도록 하세요:

Java.perform(function () {
send("Starting hooks OWASP uncrackable1...");

function getString(data){
var ret = "";
for (var i=0; i < data.length; i++){
ret += "#" + data[i].toString();
}
return ret
}

var aes_decrypt = Java.use("sg.vantagepoint.a.a");
aes_decrypt.a.overload("[B","[B").implementation = function(var_0,var_1) {
send("sg.vantagepoint.a.a.a([B[B)[B   doFinal(enc)  // AES/ECB/PKCS7Padding");
send("Key       : " + getString(var_0));
send("Encrypted : " + getString(var_1));
var ret = this.a.overload("[B","[B").call(this,var_0,var_1);
send("Decrypted : " + getString(ret));

var flag = "";
for (var i=0; i < ret.length; i++){
flag += String.fromCharCode(ret[i]);
}
send("Decrypted flag: " + flag);
return ret; //[B
};

var sysexit = Java.use("java.lang.System");
sysexit.exit.overload("int").implementation = function(var_0) {
send("java.lang.System.exit(I)V  // We avoid exiting the application  :)");
};

send("Hooks installed.");
});

Solution 2

Based in https://joshspicer.com/android-frida-1

루트 체크를 후킹하고 decrypt 함수를 수정하여 verify를 누를 때 frida 콘솔에 플래그를 출력합니다:

Java.perform(function () {
send("Starting hooks OWASP uncrackable1...");

function getString(data){
var ret = "";
for (var i=0; i < data.length; i++){
ret += "#" + data[i].toString();
}
return ret
}

var aes_decrypt = Java.use("sg.vantagepoint.a.a");
aes_decrypt.a.overload("[B","[B").implementation = function(var_0,var_1) {
send("sg.vantagepoint.a.a.a([B[B)[B   doFinal(enc)  // AES/ECB/PKCS7Padding");
send("Key       : " + getString(var_0));
send("Encrypted : " + getString(var_1));
var ret = this.a.overload("[B","[B").call(this,var_0,var_1);
send("Decrypted : " + getString(ret));

var flag = "";
for (var i=0; i < ret.length; i++){
flag += String.fromCharCode(ret[i]);
}
send("Decrypted flag: " + flag);
return ret; //[B
};

var rootcheck1 = Java.use("sg.vantagepoint.a.c");
rootcheck1.a.overload().implementation = function() {
send("sg.vantagepoint.a.c.a()Z   Root check 1 HIT!  su.exists()");
return false;
};

var rootcheck2 = Java.use("sg.vantagepoint.a.c");
rootcheck2.b.overload().implementation = function() {
send("sg.vantagepoint.a.c.b()Z  Root check 2 HIT!  test-keys");
return false;
};

var rootcheck3 = Java.use("sg.vantagepoint.a.c");
rootcheck3.c.overload().implementation = function() {
send("sg.vantagepoint.a.c.c()Z  Root check 3 HIT!  Root packages");
return false;
};

var debugcheck = Java.use("sg.vantagepoint.a.b");
debugcheck.a.overload("android.content.Context").implementation = function(var_0) {
send("sg.vantagepoint.a.b.a(Landroid/content/Context;)Z  Debug check HIT! ");
return false;
};

send("Hooks installed.");
});

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