Frida Tutorial 3

Reading time: 5 minutes

Ovo je sažetak posta: https://joshspicer.com/android-frida-1
APK: https://github.com/OWASP/owasp-mstg/blob/master/Crackmes/Android/Level_01/UnCrackable-Level1.apk

Rešenje 1

Zasnovano na https://joshspicer.com/android-frida-1

Hook the _exit()_ funkciju i decrypt function tako da ispisuje flag u frida konzoli kada pritisnete verify:

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.")
})

Rešenje 2

Bazirano na https://joshspicer.com/android-frida-1

Hook rootchecks i dekriptuje funkciju tako da ispisuje zastavicu u frida konzoli kada pritisnete verify:

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.")
})

Rešenje 3 – frida-trace (Frida ≥ 16)

Ako ne želite da ručno pišete hook-ove, možete dozvoliti Frida da generiše Java stubove za vas, a zatim ih izmenite:

# Spawn the application and automatically trace the Java method we care about
aadb shell "am force-stop owasp.mstg.uncrackable1"
frida-trace -U -f owasp.mstg.uncrackable1 \
-j 'sg.vantagepoint.a.a.a("[B","[B")[B' \
-j 'sg.vantagepoint.a.c!*' \
--output ./trace

# The first run will create ./trace/scripts/sg/vantagepoint/a/a/a__B_B_B.js
# Edit that file and add the logic that prints the decrypted flag or
# returns a constant for the root-checks, then:
frida -U -f owasp.mstg.uncrackable1 -l ./trace/_loader.js --no-pause

Sa Frida 16+ generisani stub već koristi modernu ES6 sintaksu i kompajlira se sa ugrađenim QuickJS runtime-om – više vam nije potreban frida-compile.

Rešenje 4 – Jedna linija sa Objection (2024)

Ako imate instaliran Objection >1.12 možete izvući flag sa jednom komandom (Objection obavija Frida interno):

objection -g owasp.mstg.uncrackable1 explore \
--startup-command "android hooking watch class sg.vantagepoint.a.a method a \n  && android hooking set return_value false sg.vantagepoint.a.c * \n  && android hooking invoke sg.vantagepoint.a.a a '[B' '[B'"

• watch class štampa plaintext koji vraća AES rutina
• set return_value false prisiljava svaku proveru root / debagera da prijavi false
• invoke vam omogućava da pozovete metodu direktno bez pritiska na Verify.

NAPOMENA: Na Androidu 14 (API 34) morate pokrenuti Objection/Frida u spawn režimu (-f) jer je attach blokiran seccomp-bpf ograničenjima uvedenim u oktobru 2024.

Moderni Android beleške (2023 - 2025)

• libsu 5.x i Zygisk dobro skrivaju su; međutim, Java zasnovane provere u Nivou 1 i dalje ne prolaze ako datoteka /system/bin/su postoji. Uverite se da je denylist omogućena ili jednostavno hook-ujte java.io.File.exists() sa Frida.
• Frida 16.1 je ispravila pad na Android 12/13 uzrokovan Google-ovim Scudo alokatorom. Ako vidite Abort message: 'missing SHADOW_OFFSET', nadogradite Frida (ili koristite unapred izgrađenu 17.0 nightly).
• Pošto je Play Integrity zamenio SafetyNet 2023. godine, neke novije aplikacije pozivaju com.google.android.gms.tasks.Task API. Nivo 1 to NE radi, ali ista strategija hook-ovanja prikazana ovde funkcioniše – hook-ujte com.google.android.gms.safetynet.SafetyNetClient i vratite lažirani EvaluationType.

Reference

• Frida objava verzije – "Frida 16.0 (2023-04-02): ispravke pouzdanosti za Android 12/13 i prepravka spawn API"
• Objection 1.12 – "Samo spawn režim za Android 14" (BlackHat USA 2024 prezentacione slajdove)