SQL注入

例：脚本逻辑

$sql = “SELECT * FROM user WHERE userid = $_GET[userid] “;

案例1_：SELECT * FROM t WHERE a LIKE ‘%xxx%’ OR (IF(NOW=SYSDATE(), SLEEP(5), 1)) OR b LIKE ‘1=1 ‘;_

　案例2：SELECT * FROM t WHERE a > 0 AND b IN(497 AND (SELECT * FROM (SELECT(SLEEP(20)))a) );

　案例3：SELECT * FROM t WHERE a=1 and b in (1234 ,(SELECT (CASE WHEN (5=5) THEN SLEEP(5) ELSE 5*(SELECT 5 FROM INFORMATION_SCHEMA.CHARACTER_SETS) END)) )；

监控以下方法
SLEEP() — 一般的SQL盲注都会伴随SLEEP()函数出现，而且一般至少SLEEP 5秒以上
MID()
CHAR()
ORD()
SYSDATE()
SUBSTRING()
DATABASES()
SCHEMA()
USER()
VERSION()
CURRENT_USER()
LOAD_FILE()
OUTFILE/DUMPFILE
INFORMATION_SCHEMA
TABLE_NAME
fwrite()/fopen()/file_get_contents() — 这几个是PHP文件操作函数

应对方法：

1.mysql_escape_string() 转义特殊字符（(PHP 4 >= 4.3.0, PHP 5)）(mysql_real_escape_string必须先链接上数据库，否则会报错)

下列字符受影响：
\x00 //对应于ascii字符的NULL
\n //换行符且回到下一行的最前端
\r //换行符
\ //转义符
'
"
\x1a //16进制数
如果成功，则该函数返回被转义的字符串。如果失败，则返回 false。

2.addslashes(): 函数返回在预定义字符之前添加反斜杠的字符串 (stripslashes()实现字符串还原)

预定义的字符有：
单引号（'）
双引号（"）
反斜杠（\）
NULL

3.prepared  statements(预处理机制)

connect\_errno) { echo "Failed to connect to MySQL: (" . $mysqli->connect\_errno . ") " . $mysqli->connect\_error; } /\* Non-prepared statement \*/ if (!$mysqli->query("DROP TABLE IF EXISTS test") || !$mysqli->query("CREATE TABLE test(id INT)")) { echo "Table creation failed: (" . $mysqli->errno . ") " . $mysqli->error; } /\* Prepared statement, stage 1: prepare \*/ if (!($stmt = $mysqli->prepare("INSERT INTO test(id) VALUES (?)"))) { echo "Prepare failed: (" . $mysqli->errno . ") " . $mysqli->error; } /\* Prepared statement, stage 2: bind and execute \*/ $id = 1; if (!$stmt->bind\_param("i", $id)) { echo "Binding parameters failed: (" . $stmt->errno . ") " . $stmt->error; } if (!$stmt->execute()) { echo "Execute failed: (" . $stmt->errno . ") " . $stmt->error; } ?>