进入网页发现输入什么都没反应，我们还是老办法，查看源代码，发现好像也没问题，想起外部提示，查看协议发现cookie好像有问题：
修改为1试一试：：
我们进行代码审计，发现，需要通过三层if才能得到flag
1、第一次cookie里getmein是否已经设置
2、账号为admin并且密码不为admin
3、满足cookie和md5加密后的结果
前两个比较容易通过，第三个就是hash长度扩展攻击，详细内容去一下参考看看，我也看了好久的说
http://www.freebuf.com/articles/web/69264.html
http://www.freebuf.com/articles/web/31756.html
集体我就不详细说明了，先构造出需要加密的值：
由上图我们知道位置的量长度由15位，我们随便用x来替代
key = 'x'*15+'adminadmin'+'\x80'+'\x00'*30+'\xc8'+'\x00'*7
前15是替代的，用其他的也没关系
第一个admin是用户名输入的
第二个admin以及之后的就是输入到密码栏里（注意，要把\x换为%,因为php里面还有一个解码）
\xc8是25(前面字符长度)*8位在化为16进制的结果
最后python加入应该库：（网上找的）
#!/usr/bin/env python# -*- coding: utf-8 -*-# @Author：DshtAnger# theory reference:# blog：# http://blog.csdn.net/adidala/article/details/28677393# http://blog.csdn.net/forgotaboutgirl/article/details/7258109# http://blog.sina.com.cn/s/blog_6fe0eb1901014cpl.html# RFC1321：# https://www.rfc-editor.org/rfc/pdfrfc/rfc1321.txt.pdf##############################################################################import sysdef genMsgLengthDescriptor(msg_bitsLenth):
'''
---args:
msg_bitsLenth : the bits length of raw message
--return:
16 hex-encoded string , i.e.64bits,8bytes which used to describe the bits length of raw message added after padding
'''
return __import__("struct").pack(">Q",msg_bitsLenth).encode("hex")def reverse_hex_8bytes(hex_str):
'''
--args:
hex_str: a hex-encoded string with length 16 , i.e.8bytes
--return:
transform raw message descriptor to little-endian
'''
hex_str = "%016x"%int(hex_str,16) assert len(hex_str)==16
return __import__("struct").pack("<Q",int(hex_str,16)).encode("hex")def reverse_hex_4bytes(hex_str):
'''
--args:
hex_str: a hex-encoded string with length 8 , i.e.4bytes
--return:
transform 4 bytes message block to little-endian
'''
hex_str = "%08x"%int(hex_str,16) assert len(hex_str)==8
return __import__("struct").pack("<L",int(hex_str,16)).encode("hex")def deal_rawInputMsg(input_msg):
'''
--args:
input_msg : inputed a ascii-encoded string
--return:
a hex-encoded string which can be inputed to mathematical transformation function.
'''
ascii_list = [x.encode("hex") for x in input_msg]
length_msg_bytes = len(ascii_list)
length_msg_bits = len(ascii_list)*8
#padding
ascii_list.append('80')
while (len(ascii_list)*8+64)%512 != 0:
ascii_list.append('00') #add Descriptor
ascii_list.append(reverse_hex_8bytes(genMsgLengthDescriptor(length_msg_bits))) return "".join(ascii_list)def getM16(hex_str,operatingBlockNum):
'''
--args:
hex_str : a hex-encoded string with length in integral multiple of 512bits
operatingBlockNum : message block number which is being operated , greater than 1
--return:
M : result of splited 64bytes into 4*16 message blocks with little-endian
'''
M = [int(reverse_hex_4bytes(hex_str[i:(i+8)]),16) for i in xrange(128*(operatingBlockNum-1),128*operatingBlockNum,8)] return M#定义函数，用来产生常数T[i]，常数有可能超过32位，同样需要&0xffffffff操作。注意返回的是十进制的数def T(i):
result = (int(4294967296*abs(__import__("math").sin(i))))&0xffffffff
return result
#定义每轮中用到的函数#RL为循环左移，注意左移之后可能会超过32位，所以要和0xffffffff做与运算，确保结果为32位F = lambda x,y,z:((x&y)|((~x)&z))
G = lambda x,y,z:((x&z)|(y&(~z)))
H = lambda x,y,z:(x^y^z)
I = lambda x,y,z:(y^(x|(~z)))
RL = L = lambda x,n:(((x<<n)|(x>>(32-n)))&(0xffffffff))def FF(a, b, c, d, x, s, ac):
a = (a+F ((b), (c), (d)) + (x) + (ac)&0xffffffff)&0xffffffff;
a = RL ((a), (s))&0xffffffff;
a = (a+b)&0xffffffff
return a
def GG(a, b, c, d, x, s, ac):
a = (a+G ((b), (c), (d)) + (x) + (ac)&0xffffffff)&0xffffffff;
a = RL ((a), (s))&0xffffffff;
a = (a+b)&0xffffffff
return a
def HH(a, b, c, d, x, s, ac):
a = (a+H ((b), (c), (d)) + (x) + (ac)&0xffffffff)&0xffffffff;
a = RL ((a), (s))&0xffffffff;
a = (a+b)&0xffffffff
return a
def II(a, b, c, d, x, s, ac):
a = (a+I ((b), (c), (d)) + (x) + (ac)&0xffffffff)&0xffffffff;
a = RL ((a), (s))&0xffffffff;
a = (a+b)&0xffffffff
return a
def show_md5(A,B,C,D):
return "".join( [ "".join(__import__("re").findall(r"..","%08x"%i)[::-1]) for i in (A,B,C,D) ] )def run_md5(A=0x67452301,B=0xefcdab89,C=0x98badcfe,D=0x10325476,readyMsg=""):
a = A
b = B
c = C
d = D for i in xrange(0,len(readyMsg)/128):
M = getM16(readyMsg,i+1) for i in xrange(16): exec "M"+str(i)+"=M["+str(i)+"]"
#First round
a=FF(a,b,c,d,M0,7,0xd76aa478L)
d=FF(d,a,b,c,M1,12,0xe8c7b756L)
c=FF(c,d,a,b,M2,17,0x242070dbL)
b=FF(b,c,d,a,M3,22,0xc1bdceeeL)
a=FF(a,b,c,d,M4,7,0xf57c0fafL)
d=FF(d,a,b,c,M5,12,0x4787c62aL)
c=FF(c,d,a,b,M6,17,0xa8304613L)
b=FF(b,c,d,a,M7,22,0xfd469501L)
a=FF(a,b,c,d,M8,7,0x698098d8L)
d=FF(d,a,b,c,M9,12,0x8b44f7afL)
c=FF(c,d,a,b,M10,17,0xffff5bb1L)
b=FF(b,c,d,a,M11,22,0x895cd7beL)
a=FF(a,b,c,d,M12,7,0x6b901122L)
d=FF(d,a,b,c,M13,12,0xfd987193L)
c=FF(c,d,a,b,M14,17,0xa679438eL)
b=FF(b,c,d,a,M15,22,0x49b40821L) #Second round
a=GG(a,b,c,d,M1,5,0xf61e2562L)
d=GG(d,a,b,c,M6,9,0xc040b340L)
c=GG(c,d,a,b,M11,14,0x265e5a51L)
b=GG(b,c,d,a,M0,20,0xe9b6c7aaL)
a=GG(a,b,c,d,M5,5,0xd62f105dL)
d=GG(d,a,b,c,M10,9,0x02441453L)
c=GG(c,d,a,b,M15,14,0xd8a1e681L)
b=GG(b,c,d,a,M4,20,0xe7d3fbc8L)
a=GG(a,b,c,d,M9,5,0x21e1cde6L)
d=GG(d,a,b,c,M14,9,0xc33707d6L)
c=GG(c,d,a,b,M3,14,0xf4d50d87L)
b=GG(b,c,d,a,M8,20,0x455a14edL)
a=GG(a,b,c,d,M13,5,0xa9e3e905L)
d=GG(d,a,b,c,M2,9,0xfcefa3f8L)
c=GG(c,d,a,b,M7,14,0x676f02d9L)
b=GG(b,c,d,a,M12,20,0x8d2a4c8aL) #Third round
a=HH(a,b,c,d,M5,4,0xfffa3942L)
d=HH(d,a,b,c,M8,11,0x8771f681L)
c=HH(c,d,a,b,M11,16,0x6d9d6122L)
b=HH(b,c,d,a,M14,23,0xfde5380c)
a=HH(a,b,c,d,M1,4,0xa4beea44L)
d=HH(d,a,b,c,M4,11,0x4bdecfa9L)
c=HH(c,d,a,b,M7,16,0xf6bb4b60L)
b=HH(b,c,d,a,M10,23,0xbebfbc70L)
a=HH(a,b,c,d,M13,4,0x289b7ec6L)
d=HH(d,a,b,c,M0,11,0xeaa127faL)
c=HH(c,d,a,b,M3,16,0xd4ef3085L)
b=HH(b,c,d,a,M6,23,0x04881d05L)
a=HH(a,b,c,d,M9,4,0xd9d4d039L)
d=HH(d,a,b,c,M12,11,0xe6db99e5L)
c=HH(c,d,a,b,M15,16,0x1fa27cf8L)
b=HH(b,c,d,a,M2,23,0xc4ac5665L) #Fourth round
a=II(a,b,c,d,M0,6,0xf4292244L)
d=II(d,a,b,c,M7,10,0x432aff97L)
c=II(c,d,a,b,M14,15,0xab9423a7L)
b=II(b,c,d,a,M5,21,0xfc93a039L)
a=II(a,b,c,d,M12,6,0x655b59c3L)
d=II(d,a,b,c,M3,10,0x8f0ccc92L)
c=II(c,d,a,b,M10,15,0xffeff47dL)
b=II(b,c,d,a,M1,21,0x85845dd1L)
a=II(a,b,c,d,M8,6,0x6fa87e4fL)
d=II(d,a,b,c,M15,10,0xfe2ce6e0L)
c=II(c,d,a,b,M6,15,0xa3014314L)
b=II(b,c,d,a,M13,21,0x4e0811a1L)
a=II(a,b,c,d,M4,6,0xf7537e82L)
d=II(d,a,b,c,M11,10,0xbd3af235L)
c=II(c,d,a,b,M2,15,0x2ad7d2bbL)
b=II(b,c,d,a,M9,21,0xeb86d391L)
A += a
B += b
C += c
D += d
A = A&0xffffffff
B = B&0xffffffff
C = C&0xffffffff
D = D&0xffffffff
a = A
b = B
c = C
d = D return show_md5(a,b,c,d)然后在写程序调用
#!/usr/bin/env python # -*- coding: utf-8 -*- # @Author：DshtAnger import my_md5 import hashlib import urllib #reference: # http://www.freebuf.com/articles/web/69264.html #problem link: # http://ctf4.shiyanbar.com/web/kzhan.php samplehash="571580b2 6c65f306 376d4f64 e53cb5c7" #将哈希值分为四段,并反转该四字节为小端序,作为64第二次循环的输入幻书 s1=0xb2801557 s2=0x06f3656c s3=0x644f6d37 s4=0xc7b53ce5 #exp secret = "a"*15 secret_admin="xxxxxxxxxxxxxxxadminadmin"+'\x80'+'\x00'*30+'\xc8'+'\x00'*7+"admin" r = my_md5.deal_rawInputMsg(secret_admin) inp = r[len(r)/2:] #我们需要截断的地方，也是我们需要控制的地方 #print r #print inp print "getmein:"+my_md5.run_md5(s1,s2,s3,s4,inp) print "admin"+'%80'+'%00'*30+'%c8'+'%00'*7+"admin"
即可以得到结果
这题我看来好多相关内容，基本上懂了，就是实现MD5的程序没看，所以有很多毛病，希望大家发现后指正，三口油！
