我们先来看一段代码
<?php
dbh = new PDO("mysql:host=localhost; dbname=demo", "user", "pass");
$dbh->exec("set names 'gbk'");
$sql="select * from test where name = ? and password = ?";
$stmt = $dbh->prepare($sql);
$exeres = $stmt->execute(array($name, $pass));
上面这段代码虽然使用了pdo的prepare方式来处理sql查询，但是当PHP版本<5.3.6之前还是存在宽字节SQL注入漏洞，原因在于这样的查询方式是使用了PHP本地模拟prepare，再把完整的SQL语句发送给MySQL服务器，并且有使用set names 'gbk'语句，所以会有PHP和MySQL编码不一致的原因导致SQL注入，正确的写法应该是使用ATTR_EMULATE_PREPARES 来禁用PHP本地模拟prepare，代码如下：
<?php
dbh = new PDO("mysql:host=localhost; dbname=demo", "user", "pass");
$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$dbh->exec("set names 'utf8'");
$sql="select * from test where name = ? and password = ?";
$stmt = $dbh->prepare($sql);
$exeres = $stmt->execute(array($name, $pass));
<?php
dbh = new PDO("mysql:host=localhost; dbname=demo", "user", "pass");
$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$dbh->exec("set names 'utf8'");
$sql="select * from test where name = ? and password = ?";
$stmt = $dbh->prepare($sql);
$exeres = $stmt->execute(array($name, $pass));
