引言
SQL注入是一种常见的网络攻击手段，它通过在数据库查询中插入恶意SQL代码，从而获取、修改或删除数据库中的数据。对于网络安全人员来说，了解和防范SQL注入攻击是至关重要的。本文将深入探讨中级SQL注入的实战技巧，帮助读者更好地理解和防范此类攻击。
一、SQL注入的基本原理
SQL注入攻击主要利用了Web应用程序中SQL查询语句的安全漏洞。当用户输入的数据被直接拼接到SQL查询语句中时，攻击者可以通过构造特殊的输入数据，使得SQL语句执行非预期的操作。
以下是一个简单的SQL查询示例：
SELECT * FROM users WHERE username = '$username' AND password = '$password';
如果$username和$password直接来自用户输入，而没有进行适当的验证和过滤，攻击者可以通过以下方式构造恶意输入：
' OR '1'='1
这将导致SQL语句变为：
SELECT * FROM users WHERE username = '' OR '1'='1' AND password = '';
由于'1'='1'永远为真，此查询将返回所有用户的记录。
二、中级SQL注入实战技巧
1. 报错注入
报错注入是一种利用数据库错误信息来获取敏感信息的攻击方式。以下是一个利用MySQL数据库报错注入的示例：
SELECT * FROM users WHERE username = '$username' AND password = '$password' LIMIT 1;
攻击者可以尝试以下输入：
”`sql ‘ UNION SELECT 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