CTFs | 404CTF_2024 | Retro | Bugdroid Fight

Bugdroid Fight

Here, we have the following apk.

First I converted the apk into a JAR file using the following command:

./dex-tools-v2.4/d2j-dex2jar.sh Bugdroid_Fight_-_Part_1.apk

The dex-tools came from this repo.

Now that I have the JAR file, I can open it in a Java decompiler like those and now we have access to the java source code:

We can see that it is calling MainActivityKt so we go there and have the first part of the flag:

We see under this the concatenation of 3 strings that create the flag:

So we already have Br4v0_tU_as_. We have in Utils the variable lastPart :

So now we know that the flag is Br4v0_tU_as_XXXXX_m3S5ag3!. The second part of the flag is in R.string.attr_special. But when we go to R.string.attr_special, we only have the index of this value. The string is located under a values folder into a string.xml file:

So the flag is obviously 404CTF{Br4v0_tU_as_tr0uv3_m0N_m3S5ag3!}.