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# 一、功能介绍
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AFL++是一个社区驱动的开源模糊测试工具，它是在原始的American Fuzzy Lop (AFL)的基础上发展起来的。AFL++集成了多种模糊测试技术，提供了一个可扩展的平台，允许研究人员和开发者轻松地添加新的模糊测试策略和技术。它的特点包括：
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1. **种子调度**：AFL++采用了AFLFast的调度算法，包括多种策略如 `fast`, `coe`, `explore`, `quad`, `lin`, `exploit`等，以及新增的 `mmopt`和 `rare`策略，以优化测试用例的选择和执行。
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2. **变异器**：AFL++在原有的 `havoc`和 `deterministic`变异器基础上增加了多种变异方式，包括自定义变异器API、Input-To-State变异器和MOpt Mutator，这些变异器可以提高模糊测试的效率和效果。
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3. **插桩支持**：AFL++支持多种插桩方式，包括LLVM、GCC、QEMU、Unicornafl和QBDI，以适应不同的测试需求和环境。
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4. **绕过障碍**：AFL++集成了如LAF-Intel和RedQueen等技术，这些技术可以帮助模糊测试工具绕过程序中的一些常见障碍，如复杂的字符串和校验和检查。
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5. **结构化输入变异**：AFL++支持对结构化输入进行变异，如AFLSmart，它可以利用输入模型来减少生成输入的空间，从而更有效地探索程序中的深层路径。
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6. **Custom Mutator API**：AFL++提供了自定义变异器API，允许用户根据自己的需要开发新的变异策略，这对于学术研究和特定场景的测试非常有用。
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AFL++的目标是提供一个稳定的基础，使得未来的模糊测试研究可以在此基础上进行，同时也为现有的模糊测试技术提供一个集成的平台。它与原始的AFL相比，做了大量的改进和优化，以适应快速发展的模糊测试领域。
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[AFL++项目地址](https://github.com/AFLplusplus/AFLplusplus/releases)
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# 二、编译安装
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项目推荐使用docker直接pull下来，但由于网络问题，本次示例采用在linux虚拟机上编译安装
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```shell
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git clone https://github.com/AFLplusplus/AFLplusplus # 克隆项目
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sudo apt-get install -y build-essential python3-dev automake cmake git flex bison libglib2.0-dev libpixman-1-dev python3-setuptools cargo libgtk-3-dev #安装依赖环境
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# 如果安装依赖环境出现问题，先安装下面的llvm
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sudo apt-get install -y lld-14 llvm-14 llvm-14-dev clang-14 || sudo apt-get install -y lld llvm llvm-dev clang
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sudo apt-get install -y gcc-$(gcc --version|head -n1|sed 's/\..*//'|sed 's/.* //')-plugin-dev libstdc++-$(gcc --version|head -n1|sed 's/\..*//'|sed 's/.* //')-dev
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#编译
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git clone https://github.com/AFLplusplus/AFLplusplus
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cd AFLplusplus
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make distrib
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sudo make install
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```
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安装完成后可以在使用afl-fuzz命令测试是否安装成功
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# 三、运行示例
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### （一） 目标程序的源码
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一个栈溢出案例，代码如下，当输入为abcd时会出现崩溃
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```c
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//test.c
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#include <stdio.h>
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#include <string.h>
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void vulnerable_function(char *input)
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{
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char buffer[4]; // 定义一个长度为4的字符数组
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// 复制用户输入到buffer中
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strcpy(buffer, input);
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printf("输入内容: %s\n", buffer);
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}
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int main()
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{
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char user_input[100];
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printf("请输入一串字符（以回车结束）：");
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fgets(user_input, sizeof(user_input), stdin);
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// 移除换行符
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user_input[strcspn(user_input, "\n")] = 0;
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// 检查前四个字符是否是'a', 'b', 'c', 'd'
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if (user_input[0] == 'a' ){
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if( user_input[1] == 'b' ) {
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if (user_input[2] == 'c'){
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if (user_input[3] == 'd'){
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vulnerable_function(user_input);
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}
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}
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}
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}
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return 0;
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}
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```
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### （二）模糊测试以及准备工作
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在模糊测试前先要进行**源码编译插桩**和**创建语料库**
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1. 源码编译插桩:**使用 afl++ 自带的插桩编译器**：afl-gcc
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2. 准备语料库:作为程序输入的原始材料,必须有才可以运行,原始材料越好漏洞发现的越快
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```shell
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➜ afl echo "abc" >> ./input/seed1
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```
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3. 开启模糊测试:指定必要的目标文件夹就可以开启模糊测试了
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```shell
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➜ afl afl-fuzz -i input/ -o output/ ./test
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afl-fuzz++4.22a based on afl by Michal Zalewski and a large online community
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[+] AFL++ is maintained by Marc "van Hauser" Heuse, Dominik Maier, Andrea Fioraldi and Heiko "hexcoder" Eißfeldt
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[+] AFL++ is open source, get it at https://github.com/AFLplusplus/AFLplusplus
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[+] NOTE: AFL++ >= v3 has changed defaults and behaviours - see README.md
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[+] No -M/-S set, autoconfiguring for "-S default"
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[*] Getting to work...
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[+] Using exploration-based constant power schedule (EXPLORE)
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[+] Enabled testcache with 50 MB
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[+] Generating fuzz data with a length of min=1 max=1048576
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[*] Checking core_pattern...
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[!] WARNING: Could not check CPU scaling governor
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[+] You have 16 CPU cores and 2 runnable tasks (utilization: 12%).
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[+] Try parallel jobs - see /usr/local/share/doc/afl/fuzzing_in_depth.md#c-using-multiple-cores
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[*] Setting up output directories...
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[+] Output directory exists but deemed OK to reuse.
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[*] Deleting old session data...
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[+] Output dir cleanup successful.
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[*] Checking CPU core loadout...
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[+] Found a free CPU core, try binding to #0.
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[*] Validating target binary...
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[*] Scanning 'input/'...
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[*] Creating hard links for all input files...
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[+] Loaded a total of 1 seeds.
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[*] Spinning up the fork server...
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[!] WARNING: Old fork server model is used by the target, this still works though.
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[+] All right - old fork server is up.
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[*] No auto-generated dictionary tokens to reuse.
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[*] Attempting dry run with 'id:000000,time:0,execs:0,orig:seed1'...
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len = 4, map size = 5, exec speed = 157 us, hash = ad4e684fcf34ff0e
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[+] All test cases processed.
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[+] Here are some useful stats:
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Test case count : 1 favored, 0 variable, 0 ignored, 1 total
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Bitmap range : 5 to 5 bits (average: 5.00 bits)
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Exec timing : 157 to 157 us (average: 157 us)
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[*] No -t option specified, so I'll use an exec timeout of 20 ms.
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[+] All set and ready to roll!
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american fuzzy lop ++4.22a {default} (./test) [explore]
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┌─ process timing ────────────────────────────────────┬─ overall results ────┐
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│ run time : 0 days, 0 hrs, 0 min, 1 sec │ cycles done : 15 │
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│ last new find : 0 days, 0 hrs, 0 min, 1 sec │ corpus count : 4 │
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│last saved crash : 0 days, 0 hrs, 0 min, 1 sec │saved crashes : 1 │
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│ last saved hang : none seen yet │ saved hangs : 0 │
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├─ cycle progress ─────────────────────┬─ map coverage┴──────────────────────┤
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│ now processing : 3.19 (75.0%) │ map density : 0.01% / 0.01% │
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│ runs timed out : 0 (0.00%) │ count coverage : 1.00 bits/tuple │
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├─ stage progress ─────────────────────┼─ findings in depth ─────────────────┤
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│ now trying : havoc │ favored items : 4 (100.00%) │
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│ stage execs : 85/100 (85.00%) │ new edges on : 4 (100.00%) │
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│ total execs : 10.2k │ total crashes : 5 (1 saved) │
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│ exec speed : 8074/sec │ total tmouts : 0 (0 saved) │
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├─ fuzzing strategy yields ────────────┴─────────────┬─ item geometry ───────┤
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│ bit flips : 0/32, 0/31, 0/29 │ levels : 2 │
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│ byte flips : 0/4, 0/3, 0/1 │ pending : 0 │
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│ arithmetics : 0/238, 0/25, 0/0 │ pend fav : 0 │
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│ known ints : 0/23, 0/84, 0/46 │ own finds : 3 │
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│ dictionary : 0/0, 0/0, 0/0, 0/0 │ imported : 0 │
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│havoc/splice : 1/9650, 0/0 │ stability : 100.00% │
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│py/custom/rq : unused, unused, unused, unused ├───────────────────────┘
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│ trim/eff : n/a, 25.00% │ [cpu000: 12%]
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└─ strategy: explore ────────── state: started :-) ──┘^C
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+++ Testing aborted by user +++
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[*] Writing output//default/fastresume.bin ...
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[+] Written fastresume.bin with 295308 bytes!
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[+] We're done here. Have a nice day!
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```
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4. `afl-fuzz`: 这是 AFL++ 的核心工具，用于执行模糊测试。AFL++ 是一个强大的模糊测试工具，它通过自动化生成输入数据来测试目标程序，从而发现潜在的安全漏洞或程序崩溃。
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5. `-i input/`: 这个选项指定了 AFL++ 用来开始模糊测试的初始输入种子文件的目录。在这里，`input/` 是包含初始输入数据的目录。AFL++ 会基于这些初始输入生成变异后的测试数据。
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6. `-o output/`: 这个选项指定了 AFL++ 将输出模糊测试结果的目录。`output/` 目录将包含测试过程中生成的各种数据，比如发现的崩溃或挂起的输入、统计信息等。
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7. `./test`: 这是要测试的目标程序。在这个例子中，`./test` 是你要使用 AFL++ 进行模糊测试的可执行文件。AFL++ 会向这个程序提供变异后的输入，观察它的行为（例如，是否会崩溃或触发其他异常行为）。
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### （三）验证漏洞
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崩溃的输入样本会被保存在output目录下的crashes目录，查看一下，与原先对源码分析的结果一样，也成功使程序崩溃，示例完成
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```shell
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➜ afl cat output/default/crashes/id:000000,sig:06,src:000000,time:101,execs:789,op:havoc,rep:2
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abcdcccccccccccccccccccccccc
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➜ afl ./test
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请输入一串字符（以回车结束）：abcdcccccccccccccccccccccccc
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*** buffer overflow detected ***: terminated
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[1] 1456167 IOT instruction ./test
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```
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