[原创]KCTF2021 第五题华山论剑 writeup-CTF对抗-看雪-安全社区|安全招聘|kanxue.com

[原创]KCTF2021 第五题华山论剑 writeup
发表于: 2021-5-16 12:32 7916
[原创]KCTF2021 第五题华山论剑 writeup

Wblank
2021-5-16 12:32
7916
拖进jadx java层逻辑简单，只需要关注native层stringFromJNI。
使用IDA静态分析libhello-jni.so，两个跳转让我直接懵逼，都不知道跳哪去了。
尝试用IDA调试，直接挂，有点绝望。
掏出frida，先跑了下frida-trace，结果正确的序列号弹出了“输入错误”，打不出正确的调用路径。让我直接放弃frida，绝望++。
想起之前瞥过一眼的unidbg-v0.9.3，感觉这题用它正合适。
先试着使用unidbg主动调用stringFromJNI：

能够运行和输出正确结果，感觉找对了路。
尝试使用IDA连unidbg动态调试：
emulator.attach(DebuggerType.ANDROID_SERVER_V7);
IDA附加进程后，简单跟踪了几步后，要么跑飞要么卡死...
emulator.traceCode();
traceLog看下发现ARM指令和Thumb指令来回切换。
想恢复IDA的指令静态分析，无奈找不到替代Alt+G（Change Segment Register Value）的api函数，放弃。
看着traceCode的效果:
失望，对于合格的TraceLog来说应该有寄存器的变化。
还是自己写个吧
我这东拼西凑的代码，能用就行。看着日志效果感觉还不错
正确的序列号 name:ed8b9244350d3644 serial:7C9815255BFE832D3F93140B
生成日志trace_log_true.txt，37MB的日志23w多行，直接去分析太耗时间了。
试着控制最小变量来找差异，把序列号最后一位改成C：
name:ed8b9244350d3644 serial:7C9815255BFE832D3F93140C
生成日志trace_log_flase_serial.txt，与正确的大小和行数差不多。
用BeyondCompare比较下，忽略掉push pop nop b 指令行，减少干扰。
看着这差异行并不是很多，才477个差异部分，感觉自己又可以了。
根据习惯倒着浏览差异处

0x400076a4的r4寄存器存着输入的序列号最后一位，感觉找到了关键位置。
搜索 "0x400076a4" "0x400076a8" trace_log_true.txt （匹配60次）
搜索 "0x400076a4" "0x400076a8" trace_log_flase_serial.txt （匹配60次）
看着这熟悉的序列号，算法大概是通过name算出serial后再与输入的进行异或对比。
使用 name:KCTF serial:7C9815255BFE832D3F93140B 生成trace_log_false_name_kctf.txt
搜索 "0x400076a8" "0x400076a8" trace_log_false_name_kctf.txt （匹配60次） 还好相同，说明没有少跑逻辑。
推测r5异或前就是正确的序列号
17726331DA0FE737149C8202
public void Btn1_Click(View view) {

    String str;

    String input = this.text.getText().toString();

    String input2 = this.text2.getText().toString();

    if (input == null || input.isEmpty()) {

        str = "name为空";

    } else if (input2 == null || input2.isEmpty()) {

        str = "serial为空";

    } else {

        System.loadLibrary("hello-jni");

        str = stringFromJNI(input, input2);

    }

    AlertDialog.Builder builder = new AlertDialog.Builder(mContext);

    builder.setTitle("");

    builder.setMessage(str);

    builder.show();
}
public void Btn1_Click(View view) {

    String str;

    String input = this.text.getText().toString();

    String input2 = this.text2.getText().toString();

    if (input == null || input.isEmpty()) {

        str = "name为空";

    } else if (input2 == null || input2.isEmpty()) {

        str = "serial为空";

    } else {

        System.loadLibrary("hello-jni");

        str = stringFromJNI(input, input2);

    }

    AlertDialog.Builder builder = new AlertDialog.Builder(mContext);

    builder.setTitle("");

    builder.setMessage(str);

    builder.show();
}
 
### Trace Instruction [libhello-jni.so] [0x07028] [ 01 40 84 e2 ] 0x40007028: add r4, r4, #1
### Trace Instruction [libhello-jni.so] [0x0702c] [ 01 30 43 e2 ] 0x4000702c: sub r3, r3, #1
### Trace Instruction [libhello-jni.so] [0x07030] [ ca a0 a0 e1 ] 0x40007030: asr sl, sl, #1
### Trace Instruction [libhello-jni.so] [0x07034] [ df ff ff ea ] 0x40007034: b #0x40006fb8
### Trace Instruction [libhello-jni.so] [0x06fb8] [ 0a 20 01 e0 ] 0x40006fb8: and r2, r1, sl
### Trace Instruction [libhello-jni.so] [0x06fbc] [ 52 23 a0 e1 ] 0x40006fbc: asr r2, r2, r3
### Trace Instruction [libhello-jni.so] [0x06fc0] [ 00 20 22 e2 ] 0x40006fc0: eor r2, r2, #0
### Trace Instruction [libhello-jni.so] [0x07028] [ 01 40 84 e2 ] 0x40007028: add r4, r4, #1
### Trace Instruction [libhello-jni.so] [0x0702c] [ 01 30 43 e2 ] 0x4000702c: sub r3, r3, #1
### Trace Instruction [libhello-jni.so] [0x07030] [ ca a0 a0 e1 ] 0x40007030: asr sl, sl, #1
### Trace Instruction [libhello-jni.so] [0x07034] [ df ff ff ea ] 0x40007034: b #0x40006fb8
### Trace Instruction [libhello-jni.so] [0x06fb8] [ 0a 20 01 e0 ] 0x40006fb8: and r2, r1, sl
### Trace Instruction [libhello-jni.so] [0x06fbc] [ 52 23 a0 e1 ] 0x40006fbc: asr r2, r2, r3
### Trace Instruction [libhello-jni.so] [0x06fc0] [ 00 20 22 e2 ] 0x40006fc0: eor r2, r2, #0
package com.kctf;
 
import capstone.Capstone;

import com.github.unidbg.AndroidEmulator;

import com.github.unidbg.Emulator;

import com.github.unidbg.Module;

import com.github.unidbg.Symbol;

import com.github.unidbg.arm.ARM;

import com.github.unidbg.arm.HookStatus;

import com.github.unidbg.arm.backend.Backend;

import com.github.unidbg.arm.backend.CodeHook;

import com.github.unidbg.arm.backend.DebugHook;

import com.github.unidbg.arm.context.Arm32RegisterContext;

import com.github.unidbg.arm.context.RegisterContext;

import com.github.unidbg.debugger.DebuggerType;

import com.github.unidbg.hook.HookContext;

import com.github.unidbg.hook.ReplaceCallback;

import com.github.unidbg.hook.hookzz.*;

import com.github.unidbg.hook.xhook.IxHook;

import com.github.unidbg.linux.android.AndroidEmulatorBuilder;

import com.github.unidbg.linux.android.AndroidResolver;

import com.github.unidbg.linux.android.XHookImpl;

import com.github.unidbg.linux.android.dvm.AbstractJni;

import com.github.unidbg.linux.android.dvm.DalvikModule;

import com.github.unidbg.linux.android.dvm.DvmClass;

import com.github.unidbg.linux.android.dvm.VM;

import com.github.unidbg.linux.android.dvm.array.ByteArray;

import com.github.unidbg.memory.Memory;

import com.github.unidbg.utils.Inspector;

import com.sun.jna.Pointer;

import unicorn.ArmConst;
 
import java.io.*;

import java.nio.charset.StandardCharsets;

import java.util.*;
 
public class hellojni extends AbstractJni {
 
    private final AndroidEmulator emulator;

    private final VM vm;

    private final Module module;
 
    private final DvmClass hellojniUtils;
 
    private final boolean logging;
 
    private final Set<Integer> trace_addr;

    private final Map<Integer, String> insn_map;

    private final Map<Integer, Integer> insn_size;

    private String lastContent;

    private int[] lastReg;
 
    hellojni(boolean logging) {

        lastContent = "";

        lastReg = null;

        trace_addr = new TreeSet<Integer>();

        insn_map = new TreeMap<Integer, String>();

        insn_size = new TreeMap<>();

        this.logging = logging;

        emulator = AndroidEmulatorBuilder.for32Bit().setProcessName("com.example.hellojni").build(); // 创建模拟器实例，要模拟32位或者64位，在这里区分

        final Memory memory = emulator.getMemory(); // 模拟器的内存操作接口

        memory.setLibraryResolver(new AndroidResolver(23)); // 设置系统类库解析
 
        vm = emulator.createDalvikVM(null); // 创建Android虚拟机
 
        vm.setJni(this);

        vm.setVerbose(logging); // 设置是否打印Jni调用细节

        DalvikModule dm = vm.loadLibrary(new File("unidbg-android/src/test/resources/example_binaries/libhello-jni.so"), true); // 加载libhello-jni.so到unicorn虚拟内存，加载成功以后会默认调用init_array等函数

        dm.callJNI_OnLoad(emulator); // 手动执行JNI_OnLoad函数

        module = dm.getModule(); // 加载好的libhello-jni.so对应为一个模块
 
        //com_example_hellojni_HelloJni_

        hellojniUtils = vm.resolveClass("com/example/hellojni/HelloJni");

    }
 
    void destroy() throws IOException {

        Object[] itr = trace_addr.toArray();

        File f = new File("E:/out.txt");

        FileWriter fw = new FileWriter(f);

        for (Object i : itr) {

//            System.out.println(String.format("set_color(0x%x, CIC_FUNC, 0xd3d3d3) %s", (Integer) i, insn_map.get(i)));

//            fw.write(insn_map.get(i));

            fw.write(String.format("setreg(0x%x, %d)\n", i, insn_size.get(i)));

        }

        fw.close();
 
        emulator.close();

        if (logging) {

            System.out.println("destroy");

        }

    }
 
    public static void main(String[] args) throws Exception {

        com.kctf.hellojni test = new com.kctf.hellojni(true);
 
        String data = test.stringFromJNI("ed8b9244350d3644", "7C9815255BFE832D3F93140B");

        System.out.println(data);

        test.destroy();

    }
 
    public static int[] getReg(String reg) {

        int[] ret = new int[1];

        switch (reg) {

            case "r0": ret[0] = ArmConst.UC_ARM_REG_R0; break;

            case "r1": ret[0] = ArmConst.UC_ARM_REG_R1; break;

            case "r2": ret[0] = ArmConst.UC_ARM_REG_R2; break;

            case "r3": ret[0] = ArmConst.UC_ARM_REG_R3; break;

            case "r4": ret[0] = ArmConst.UC_ARM_REG_R4; break;

            case "r5": ret[0] = ArmConst.UC_ARM_REG_R5; break;

            case "r6": ret[0] = ArmConst.UC_ARM_REG_R6; break;

            case "r7": ret[0] = ArmConst.UC_ARM_REG_R7; break;

            case "r8": ret[0] = ArmConst.UC_ARM_REG_R8; break;

            case "r9": ret[0] = ArmConst.UC_ARM_REG_R9; break;

            case "r10": ret[0] = ArmConst.UC_ARM_REG_R10; break;

            case "r11": ret[0] = ArmConst.UC_ARM_REG_R11; break;

            case "r12": ret[0] = ArmConst.UC_ARM_REG_R12; break;

            case "pc": ret[0] = ArmConst.UC_ARM_REG_PC; break;

            case "sp": ret[0] = ArmConst.UC_ARM_REG_SP; break;

            case "lr": ret[0] = ArmConst.UC_ARM_REG_LR; break;

            case "sb": ret[0] = ArmConst.UC_ARM_REG_SB; break;

            default: return null;

        }

        return ret;

    }
 
    String getMemStr(Backend backend, int addr) {

        StringBuilder builder = new StringBuilder();

        a:

        do {

            try {

                byte[] bytes = backend.mem_read(addr, 1);

                for (int i = 0; i < bytes.length; i++) {

                    int fb = bytes[i];

                    if (fb <= 31 || fb >= 127)

                        break a;

                    builder.append(String.format("%c",fb));

                }

                addr++;

            } catch (Exception e) {

                return "";

            }

        } while (true);

        return builder.toString();

    }
 
    String stringFromJNI(String name, String serial) {

        if(false)

        {

            Object ret = hellojniUtils.callStaticJniMethodObject(emulator, "stringFromJNI(Ljava/lang/String;Ljava/lang/String)Ljava/lang/String", name, serial); // 执行Jni方法

            return ret.toString();

        }

        // so function address

        final Set<Integer> st = new TreeSet<Integer>() {{

            Integer[] a = new Integer[]{0xff5, 0x1035, 0x10e5, 0x1421, 0x1438, 0x14dc, 0x152c, 0x1634, 0x16c0, 0x1724, 0x1854, 0x1914, 0x19c4, 0x1a48, 0x1aa4, 0x1ad0, 0x1b98, 0x1fa4, 0x2350, 0x2394, 0x24b4, 0x2540, 0x28c8};

            for (Integer b : a) {

                add(b);

            }

        }};

        emulator.getBackend().hook_add_new(new DebugHook() {

            @Override

            public void onBreak(Backend backend, long address, int size, Object user) {

            }
 
            @Override

            public void hook(Backend backend, long address, int size, Object user) {

                //打印当前地址。这里要把unidbg使用的基址给去掉。

                int addr = (int) address - 0x40000000;

                trace_addr.add(addr);

                if (st.contains(addr + 1)) {

//                    System.out.println(String.format("0x%x", addr));

                }

//

                if (false) {

                    Capstone.CsInsn[] insns = emulator.printAssemble(System.out, address, size);

//                    ARM.showRegs(emulator, ARM.getRegArgs(emulator));

                }

                if (true) {

                    ByteArrayOutputStream baos = new ByteArrayOutputStream();

                    PrintStream ps = null;

                    try {

                        ps = new PrintStream(baos, true, "utf-8");

                    } catch (IOException e) {

                    }

                    Capstone.CsInsn[] insns = emulator.printAssemble(ps, address, size);

                    String content = new String(baos.toByteArray(), StandardCharsets.UTF_8);

                    content = content.replace('\n', ' ');

                    ps.close();

                    String regStr = "";

                    for (int i = 0; i < insns.length; i++) {

                        regStr = insns[i].opStr.split(",")[0];

                    }

                    int[] regs = getReg(regStr);

                    if (regs != null) {

                        content = content + " >>> " + regStr + "=" + "0x%x";

                    }

                    if (lastReg == null) {

                        System.out.print(lastContent);

                        ARM.showRegs(emulator, null);

                    } else {

                        int value = backend.reg_read(lastReg[0]).intValue();

                        String memStr = getMemStr(backend, value);

                        if (!memStr.equals("")) {

                            memStr = "\"" + memStr + "\"";

                        }

                        System.out.println(String.format(lastContent, value) + " " + memStr);
 
                    }
 
                    lastContent = content;

                    lastReg = regs;

                    if (!insn_map.containsKey(addr)) {

                        insn_map.put(addr, content);

                        insn_size.put(addr, (int) insns[0].size);

                    }

                }

            }

        }, 0x40000ff4, 0x400076BC, null);

//        emulator.traceCode();

//        emulator.traceWrite();

//        emulator.traceRead();

//        emulator.attach(DebuggerType.ANDROID_SERVER_V7); // 附加IDA android_server，可输入c命令取消附加继续运行

        Object ret = hellojniUtils.callStaticJniMethodObject(emulator, "stringFromJNI(Ljava/lang/String;Ljava/lang/String)Ljava/lang/String", name, serial); // 执行Jni方法

        return ret.toString();

    }
 
}
package com.kctf;
 
import capstone.Capstone;

import com.github.unidbg.AndroidEmulator;

import com.github.unidbg.Emulator;

import com.github.unidbg.Module;

import com.github.unidbg.Symbol;

import com.github.unidbg.arm.ARM;

import com.github.unidbg.arm.HookStatus;

import com.github.unidbg.arm.backend.Backend;

import com.github.unidbg.arm.backend.CodeHook;

import com.github.unidbg.arm.backend.DebugHook;

import com.github.unidbg.arm.context.Arm32RegisterContext;

import com.github.unidbg.arm.context.RegisterContext;

import com.github.unidbg.debugger.DebuggerType;

import com.github.unidbg.hook.HookContext;

import com.github.unidbg.hook.ReplaceCallback;

import com.github.unidbg.hook.hookzz.*;

import com.github.unidbg.hook.xhook.IxHook;

import com.github.unidbg.linux.android.AndroidEmulatorBuilder;

import com.github.unidbg.linux.android.AndroidResolver;

import com.github.unidbg.linux.android.XHookImpl;

import com.github.unidbg.linux.android.dvm.AbstractJni;

import com.github.unidbg.linux.android.dvm.DalvikModule;

import com.github.unidbg.linux.android.dvm.DvmClass;

import com.github.unidbg.linux.android.dvm.VM;

import com.github.unidbg.linux.android.dvm.array.ByteArray;

import com.github.unidbg.memory.Memory;

import com.github.unidbg.utils.Inspector;

import com.sun.jna.Pointer;

import unicorn.ArmConst;
 
import java.io.*;

import java.nio.charset.StandardCharsets;

import java.util.*;
 
public class hellojni extends AbstractJni {
 
    private final AndroidEmulator emulator;

    private final VM vm;

    private final Module module;
 
    private final DvmClass hellojniUtils;
 
    private final boolean logging;
 
    private final Set<Integer> trace_addr;

    private final Map<Integer, String> insn_map;

    private final Map<Integer, Integer> insn_size;

    private String lastContent;

    private int[] lastReg;
 
    hellojni(boolean logging) {

        lastContent = "";

        lastReg = null;

        trace_addr = new TreeSet<Integer>();

        insn_map = new TreeMap<Integer, String>();

        insn_size = new TreeMap<>();

        this.logging = logging;

        emulator = AndroidEmulatorBuilder.for32Bit().setProcessName("com.example.hellojni").build(); // 创建模拟器实例，要模拟32位或者64位，在这里区分

        final Memory memory = emulator.getMemory(); // 模拟器的内存操作接口

        memory.setLibraryResolver(new AndroidResolver(23)); // 设置系统类库解析
 
        vm = emulator.createDalvikVM(null); // 创建Android虚拟机
 
        vm.setJni(this);

        vm.setVerbose(logging); // 设置是否打印Jni调用细节

        DalvikModule dm = vm.loadLibrary(new File("unidbg-android/src/test/resources/example_binaries/libhello-jni.so"), true); // 加载libhello-jni.so到unicorn虚拟内存，加载成功以后会默认调用init_array等函数

        dm.callJNI_OnLoad(emulator); // 手动执行JNI_OnLoad函数

        module = dm.getModule(); // 加载好的libhello-jni.so对应为一个模块
 
        //com_example_hellojni_HelloJni_

        hellojniUtils = vm.resolveClass("com/example/hellojni/HelloJni");

    }
 
    void destroy() throws IOException {

        Object[] itr = trace_addr.toArray();

        File f = new File("E:/out.txt");

        FileWriter fw = new FileWriter(f);

        for (Object i : itr) {

//            System.out.println(String.format("set_color(0x%x, CIC_FUNC, 0xd3d3d3) %s", (Integer) i, insn_map.get(i)));

//            fw.write(insn_map.get(i));

            fw.write(String.format("setreg(0x%x, %d)\n", i, insn_size.get(i)));

        }

        fw.close();
 
        emulator.close();

        if (logging) {

            System.out.println("destroy");

        }

    }
 
    public static void main(String[] args) throws Exception {

        com.kctf.hellojni test = new com.kctf.hellojni(true);
 
        String data = test.stringFromJNI("ed8b9244350d3644", "7C9815255BFE832D3F93140B");

        System.out.println(data);

        test.destroy();

    }
 
    public static int[] getReg(String reg) {

        int[] ret = new int[1];

        switch (reg) {

            case "r0": ret[0] = ArmConst.UC_ARM_REG_R0; break;

            case "r1": ret[0] = ArmConst.UC_ARM_REG_R1; break;

            case "r2": ret[0] = ArmConst.UC_ARM_REG_R2; break;

            case "r3": ret[0] = ArmConst.UC_ARM_REG_R3; break;

            case "r4": ret[0] = ArmConst.UC_ARM_REG_R4; break;

            case "r5": ret[0] = ArmConst.UC_ARM_REG_R5; break;

            case "r6": ret[0] = ArmConst.UC_ARM_REG_R6; break;

            case "r7": ret[0] = ArmConst.UC_ARM_REG_R7; break;

            case "r8": ret[0] = ArmConst.UC_ARM_REG_R8; break;

            case "r9": ret[0] = ArmConst.UC_ARM_REG_R9; break;

            case "r10": ret[0] = ArmConst.UC_ARM_REG_R10; break;

            case "r11": ret[0] = ArmConst.UC_ARM_REG_R11; break;

            case "r12": ret[0] = ArmConst.UC_ARM_REG_R12; break;

            case "pc": ret[0] = ArmConst.UC_ARM_REG_PC; break;

            case "sp": ret[0] = ArmConst.UC_ARM_REG_SP; break;

            case "lr": ret[0] = ArmConst.UC_ARM_REG_LR; break;

            case "sb": ret[0] = ArmConst.UC_ARM_REG_SB; break;

            default: return null;

        }

        return ret;

    }
 
    String getMemStr(Backend backend, int addr) {

        StringBuilder builder = new StringBuilder();

        a:

        do {

            try {

                byte[] bytes = backend.mem_read(addr, 1);

                for (int i = 0; i < bytes.length; i++) {

                    int fb = bytes[i];

                    if (fb <= 31 || fb >= 127)

                        break a;

                    builder.append(String.format("%c",fb));

                }

                addr++;

            } catch (Exception e) {

                return "";

            }

        } while (true);

        return builder.toString();

    }
 
    String stringFromJNI(String name, String serial) {

        if(false)

        {

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[招生]科锐逆向工程师培训(2024年11月15日实地，远程教学同时开班, 第51期)

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AJISky 雪币： 269 活跃值： (906) 能力值： ( LV12，RANK：345 ) 在线值：发帖 44 回帖 515 粉丝 21 关注私信	AJISky 7 2 楼棒棒的，下次把eor拿掉，太简单了 2021-5-17 14:43 0
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[原创]KCTF2021 第五题 华山论剑 writeup

[原创]KCTF2021 第五题华山论剑 writeup
