漏洞挖掘和FUZZ技术 – 作者:无情剑客Burning-安全小百科

声明：谢绝一切形式的转载。

在计算机的世界中，有输入的地方就有江湖，因为有输入的地方，就有可能有漏洞。比如xss，目前很多大型网站依然存在xss漏洞。

一个简单的程序

下面的程序是求一个数的平方。

#include<stdio.h>

int main(){

        int a =0;

        scanf("%d",&a);

        printf("%d\n",a*a);

        return 0;

}

编译gcc test.c运行./a.out通过观察，很容易看出当输入一些”畸形”数据的时候会导致程序运行出现错误。如果只有二进制文件，有什么办法可以检测出这种错误？

Fuzz

A software testing technique, often automated or semi-automated, that involves passing invalid, unexpected or random input to a program and monitor result for crashes, failed assertions, races, leaks, etc.

术语

Target

Consumes an array of bytes

Calls the code we want to test

Fuzzer

A tool that feed the target with different random inputs

Corpus

A set of valid & invalid inputs for the target

Collected manually, by fuzzing, or by crawling

fuzz的种类

Generation Based ：通过对目标协议或文件格式建模的方法，从零开始产生测试用例，没有先前的状态

Mutation Based ：基于一些规则，从已有的数据样本或存在的状态变异

Evolutionary ：包含了上述两种，同时会根据代码覆盖率的回馈进行变异。

传统fuzz

传统的 fuzz 大多通过对已有的样本按照预先设置好的规则进行变异产生测试用例，然后喂给目标程序同时监控目标程序的运行状态。这类 fuzz 有很多，比如: peach , FileFuzz 等。

实战

相关文件位于:https://github.com/Dor1s/libfuzzer-workshop/tree/master/lessons/02

生成测试用例

radamsa 是一个测试用例生成引擎，它是通过对已有的样本进行变异来生成新的测试用例。下面的代码主要通过调用 radamsa ,然后随机选取 seed_corpus 目录中的文件名作为参数，传递给 radamsa 进行变异，把生成的测试用例，放到 work/corpus。

#!/usr/bin/env python2

# generate_testcases.py

import os

import random

WORK_DIR = 'work'

# Create work `directory` and `corpus` subdirectory.

if not os.path.exists(WORK_DIR):

os.mkdir(WORK_DIR)

corpus_dir = os.path.join(WORK_DIR, 'corpus')

if not os.path.exists(corpus_dir):

os.mkdir(corpus_dir)

seed_corpus_filenames = os.listdir('seed_corpus')

for i in xrange(1000):

random_seed_filename = random.choice(seed_corpus_filenames)

random_seed_filename = os.path.join('seed_corpus', random_seed_filename)

output_filename = os.path.join(WORK_DIR, 'corpus', 'testcase-%06d' % i)

cmd = 'bin/radamsa "%s" > "%s"' % (random_seed_filename, output_filename)

os.popen(cmd)

开始fuzz

fuzz程序如下，target是vscode，Corpus是上面程序生成的测试用例。

#!/usr/bin/env python2

# run_fuzzing.py

import os

import subprocess




WORK_DIR = 'work'




def checkOutput(s):

if 'Segmentation fault' in s or 'error' in s.lower():

return False

else:

return True




corpus_dir = os.path.join(WORK_DIR, 'corpus')

corpus_filenames = os.listdir(corpus_dir)




for f in corpus_filenames:

testcase_path = os.path.join(corpus_dir, f)

cmd = ['/usr/bin/code', testcase_path]

process = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE,stderr=subprocess.STDOUT)

output = process.communicate()[0]

if not checkOutput(output):

print testcase_path

print output

print '-' * 80

由于用于变异样本的选取和样本的变异方式是随机的，可能需要重复多次样本生成 && fuzz 才能找到 crash。写个 bash 脚本，不断重复即可。

#!/bin/bash

while [ "0" -lt "1" ]

do

rm -rf ./work/

./generate_testcases.py

./run_fuzzing.py

done

libFuzzer

feature

In-process, in-memory

Guided fuzz testing

Very effective at a function / protocol level

1000x faster

It’s easy to write a libFuzzer-based fuzzer

Can be checked along with unit-tests

Memory Tools

● AddressSanitizer (aka ASan)

Detects use-after-free, buffer overflows (heap, stack, globals), stack-use-after-return, container-overflow

Cpu: 2x, memory 1.5x-3x

● MemorySanitizer (aka MSan)

Detects uninitialized memory reads

Cpu: 3x, memory: 2x

Special mode: origins

● UndefinedBehaviorSanitizer (aka UBSan)

Detects several classes of bugs (19?), esp on type confusion, signed-integer-overflow, undefined shift, etc.

Cpu: 10-50%

Memory: ~1x (no allocator, no shadow)

Helloworld-For-libFuzzer

本节资源位于:https://github.com/Dor1s/libfuzzer-workshop/tree/master/lessons/04。

target

bool VulnerableFunction1(const uint8_t* data, size_t size) {

bool result = false;

if (size >= 3) {

result = data[0] == 'F' &&

data[1] == 'U' &&

data[2] == 'Z' &&

data[3] == 'Z';

}

return result;

}

在上面的程序中，当size=3的时候，访问data[3]会产生越界。

fuzzer

first_fuzzer.cc

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {

VulnerableFunction1(data, size);

return 0;

}

编译：clang++-g-fsanitize=address,fuzzer first_fuzzer.cc运行fuzzer:./a.out2>&1|grep ERROR完整的输出

INFO: Seed: 100908111

INFO: Loaded 1 modules (35 inline 8-bit counters): 35 [0x7f8120, 0x7f8143),

INFO: Loaded 1 PC tables (35 PCs): 35 [0x5b7f68,0x5b8198),

INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes

INFO: A corpus is not provided, starting from an empty corpus

#2 INITED cov: 3 ft: 3 corp: 1/1b exec/s: 0 rss: 27Mb

#15 NEW cov: 4 ft: 4 corp: 2/4b lim: 4 exec/s: 0 rss: 27Mb L: 3/3 MS: 3 CopyPart-CrossOver-InsertByte-

#1156 NEW cov: 5 ft: 5 corp: 3/7b lim: 14 exec/s: 0 rss: 27Mb L: 3/3 MS: 1 CMP- DE: "F\x00"-

#2688 NEW cov: 6 ft: 6 corp: 4/15b lim: 29 exec/s: 0 rss: 27Mb L: 8/8 MS: 2 ChangeByte-InsertRepeatedBytes-

#2704 REDUCE cov: 6 ft: 6 corp: 4/13b lim: 29 exec/s: 0 rss: 28Mb L: 6/6 MS: 1 EraseBytes-

#2844 REDUCE cov: 6 ft: 6 corp: 4/12b lim: 29 exec/s: 0 rss: 28Mb L: 5/5 MS: 5 CrossOver-PersAutoDict-CrossOver-EraseBytes-EraseBytes- DE: "F\x00"-

#3080 REDUCE cov: 6 ft: 6 corp: 4/11b lim: 29 exec/s: 0 rss: 28Mb L: 4/4 MS: 1 EraseBytes-

#3172 REDUCE cov: 6 ft: 6 corp: 4/10b lim: 29 exec/s: 0 rss: 28Mb L: 3/3 MS: 2 CopyPart-EraseBytes-

#10828 REDUCE cov: 7 ft: 7 corp: 5/70b lim: 104 exec/s: 0 rss: 28Mb L: 60/60 MS: 1 InsertRepeatedBytes-

#10840 REDUCE cov: 7 ft: 7 corp: 5/29b lim: 104 exec/s: 0 rss: 28Mb L: 19/19 MS: 2 PersAutoDict-CrossOver- DE: "F\x00"-

#10933 REDUCE cov: 7 ft: 7 corp: 5/24b lim: 104 exec/s: 0 rss: 28Mb L: 14/14 MS: 3 ChangeByte-InsertByte-EraseBytes-

#11125 REDUCE cov: 7 ft: 7 corp: 5/21b lim: 104 exec/s: 0 rss: 28Mb L: 11/11 MS: 2 InsertByte-EraseBytes-

#11361 REDUCE cov: 7 ft: 7 corp: 5/18b lim: 104 exec/s: 0 rss: 28Mb L: 8/8 MS: 1 EraseBytes-

#11482 REDUCE cov: 7 ft: 7 corp: 5/14b lim: 104 exec/s: 0 rss: 28Mb L: 4/4 MS: 1 EraseBytes-

=================================================================

==3357==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000040f73 at pc 0x00000059b461 bp 0x7fff657ee560 sp 0x7fff657ee558

READ of size 1 at 0x602000040f73 thread T0

#0 0x59b460 in VulnerableFunction1(unsigned char const*, unsigned long) /home/burning/linux/libfuzzer-workshop-master/lessons/04/./vulnerable_functions.h:22:14

#1 0x59bde4 in LLVMFuzzerTestOneInput /home/burning/linux/libfuzzer-workshop-master/lessons/04/first_fuzzer.cc:10:3

#2 0x466186 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:556

#3 0x46b7e9 in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool*) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:470

#4 0x46b7e9 in fuzzer::Fuzzer::MutateAndTestOne() /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:699

#5 0x46e80f in fuzzer::Fuzzer::Loop(std::Fuzzer::vector<fuzzer::SizedFile, fuzzer::fuzzer_allocator<fuzzer::SizedFile> >&) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:830

#6 0x456b99 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:824

#7 0x41f522 in main /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerMain.cpp:19

#8 0x7fa043c3eb96 in __libc_start_main /build/glibc-2ORdQG/glibc-2.27/csu/../csu/libc-start.c:310

#9 0x41f599 in _start (/home/burning/linux/libfuzzer-workshop-master/lessons/04/a.out+0x41f599)




0x602000040f73 is located 0 bytes to the right of 3-byte region [0x602000040f70,0x602000040f73)

allocated by thread T0 here:

#0 0x597*** in operator new[](unsigned long) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/asan/asan_new_delete.cpp:102

#1 0x466092 in fuzzer::Fuzzer::ExecuteCallback(unsigned char const*, unsigned long) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:541

#2 0x46b7e9 in fuzzer::Fuzzer::RunOne(unsigned char const*, unsigned long, bool, fuzzer::InputInfo*, bool*) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:470

#3 0x46b7e9 in fuzzer::Fuzzer::MutateAndTestOne() /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:699

#4 0x46e80f in fuzzer::Fuzzer::Loop(std::Fuzzer::vector<fuzzer::SizedFile, fuzzer::fuzzer_allocator<fuzzer::SizedFile> >&) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:830

#5 0x456b99 in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char const*, unsigned long)) /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:824

#6 0x41f522 in main /home/burning/linux/libfuzzer-workshop-master/src/llvm/projects/compiler-rt/lib/fuzzer/FuzzerMain.cpp:19

#7 0x7fa043c3eb96 in __libc_start_main /build/glibc-2ORdQG/glibc-2.27/csu/../csu/libc-start.c:310




SUMMARY: AddressSanitizer: heap-buffer-overflow /home/burning/linux/libfuzzer-workshop-master/lessons/04/./vulnerable_functions.h:22:14 in VulnerableFunction1(unsigned char const*, unsigned long)

Shadow bytes around the buggy address:

0x0c0480000190: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fd fa

0x0c04800001a0: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fd fa

0x0c04800001b0: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fd fa

0x0c04800001c0: fa fa fd fd fa fa fd fd fa fa fd fa fa fa fd fa

0x0c04800001d0: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fd fa

=>0x0c04800001e0: fa fa fd fa fa fa fd fa fa fa fd fa fa fa[03]fa

0x0c04800001f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa

0x0c0480000200: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa

0x0c0480000210: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa

0x0c0480000220: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa

0x0c0480000230: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa

Shadow byte legend (one shadow byte represents 8 application bytes):

Addressable: 00

Partially addressable: 01 02 03 04 05 06 07

Heap left redzone: fa

Freed heap region: fd

Stack left redzone: f1

Stack mid redzone: f2

Stack right redzone: f3

Stack after return: f5

Stack use after scope: f8

Global redzone: f9

Global init order: f6

Poisoned by user: f7

Container overflow: fc

Array cookie: ac

Intra object redzone: bb

ASan internal: fe

Left alloca redzone: ca

Right alloca redzone: cb

Shadow gap: cc

==3357==ABORTING

MS: 5 CopyPart-EraseBytes-PersAutoDict-EraseBytes-ChangeBinInt- DE: "F\x00"-; base unit: 9dbab5c181e3d878fa7e1229929a99dc1f04abf4

0x46,0x55,0x5a,

FUZ

artifact_prefix='./'; Test unit written to ./crash-0eb8e4ed029b774d80f2b66408203801cb982a60

正常的话应该可以看到类似上面的输出，这里对其中的一些信息解析一下

Seed: 1608565063 说明这次的种子数据

max_len 用于设置最大的数据长度

接下来 # 开头的行是 fuzz 过程中找到的路径信息

最后一行是触发漏洞的测试用例

重现crash:

ASAN_OPTIONS=symbolize=1 ./a.out ./crash-0eb8e4ed029b774d80f2b66408203801cb982a60

# ASAN_OPTIONS=symbolize=1 用于显示 栈的符号信息

写在最后

文章中涉及到很多英文内容，个人不能翻译到信、达、雅的地步，所以就保留原文了。

来源：freebuf.com 2020-07-22 21:40:56 by: 无情剑客Burning

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