Java? - Securinets CTF Quals 2024

Mon, 21 Oct 2024 10:02:00 +0200

Last week we qualified for securinets finals. Java? was a pwn challenge I blooded. We were given a java program, which reads input three times and passes it to a library:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

 private String first = "";
 private String second = "";
 private String last = "";

 static {
 System.loadLibrary("Lib");
 }

 public native void Kabom();
 public native void Setup();

 public static void main(String[] args) throws IOException{
 BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
 Main me = new Main();

 me.Setup();

 //System.out.println("If I give you a gift, will you give me the right input? ");
 //me.Gift();

 System.out.println("And I'll give you 3 bullets");

 System.out.println("First shot: ");
 me.first = reader.readLine();

 System.out.println("Second shot: ");
 me.second = reader.readLine();

 System.out.println("Last shot: ");
 me.last = reader.readLine();

 me.Kabom();
 }
}

The library provided prints the three inputs with printf, resulting in a format string vuln.

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Java? - Securinets CTF Quals 2024