PHP防SQL注入和XSS攻击

摘要：就是通过把SQL命令插入到Web表单提交或输入域名或页面请求的查询字符串，最终达到欺骗服务器执行恶意的SQL命令.在用户名输入框中输入:\' or 1=1#,密码随便输入，这时候的合成后的SQL查询语句为“#”在mysql中是注释符，这样井号后面的内容将被mysql视为注释内容，这样就不会去执行了,...

就是通过把SQL命令插入到Web表单提交或输入域名或页面请求的查询字符串，最终达到欺骗服务器执行恶意的SQL命令.在用户名输入框中输入:\' or 1=1#,密码随便输入，这时候的合成后的SQL查询语句为“#”在mysql中是注释符，这样井号后面的内容将被mysql视为注释内容，这样就不会去执行了,等价于

1 select * from users where username=\'\' or 1=1

防止SQL注入

 1 <?php  
 2 $field = explode(\',\', $data);  
 3 array_walk($field, array($this, \'add_special_char\'));  
 4 $data = implode(\',\', $field);  
 5 /** 
 6  * 对字段两边加反引号，以保证数据库安全 
 7  * @param $value 数组值 
 8  */  
 9 function add_special_char(&$value)  
10 {  
11     if (\'*\' == $value || false !== strpos($value, \'(\') || false !== strpos($value, \'.\') || false !== strpos($value, \'`\')) {  
12         //不处理包含* 或者 使用了sql方法。  
13     } else {  
14         $value = \'`\' . trim($value) . \'`\';  
15     }  
16     return $value;  
17 }  
18   
19 /* 
20 函数名称：inject_check() 
21 函数作用：检测提交的值是不是含有SQL注入的字符,保护服务器安全 
22 参　　数：$sql_str: 提交的变量inject_check($id) { exit(\'提交的参数非法！\'); 
23 返 回 值：返回检测结果，true or false 
24 */  
25 function inject_check($sql_str)  
26 {  
27     return preg_match(\'/^select|insert|and|or|create|update|delete|alter|count|\\'|\/\*|\*|\.\.\/|\.\/|union|into|load_file|outfile/i\', $sql_str); // 进行过滤  
28 }  
29   
30 //递归ddslashes  
31 function daddslashes($string, $force = 0, $strip = FALSE)  
32 {  
33     if (!get_magic_quotes_gpc() || $force) {  
34         if (is_array($string)) {  
35             foreach ($string as $key => $val) {  
36                 $string [$key] = daddslashes($val, $force);  
37             }  
38         } else {  
39             $string = addslashes($strip ? stripslashes($string) : $string);  
40         }  
41     }  
42     return $string;  
43 }  
44   
45 //递归stripslashes  
46 function dstripslashes($string)  
47 {  
48     if (is_array($string)) {  
49         foreach ($string as $key => $val) {  
50             $string [$key] = $this->dstripslashes($val);  
51         }  
52     } else {  
53         $string = stripslashes($string);  
54     }  
55     return $string;  
56 }

CSRF攻击(跨站请求伪造)原理比较简单，如图1所示。
其中Web A为存在CSRF漏洞的网站，Web B为攻击者构建的恶意网站，User C为Web A网站的合法用户。

1. 用户C打开浏览器，访问受信任网站A，输入用户名和密码请求登录网站A；
2.在用户信息通过验证后，网站A产生Cookie信息并返回给浏览器，此时用户登录网站A成功，可以正常发送请求到网站A；
3. 用户未退出网站A之前，在同一浏览器中，打开一个TAB页访问网站B；
4. 网站B接收到用户请求后，返回一些攻击性代码，并发出一个请求要求访问第三方站点A；
5. 浏览器在接收到这些攻击性代码后，根据网站B的请求，在用户不知情的情况下携带Cookie信息，向网站A发出请求。网站A并不知道该请求其实是由B发起的，所以会根据用户C的Cookie信息以C的权限处理该请求，导致来自网站B的恶意代码被执行。

网站A

<?php
session_start();
if (isset($_POST[\'toBankId\']) && isset($_POST[\'money\'])) {
buy_stocks($_POST[\'toBankId\'],　$_POST[\'money\']);
}
?>

危险网站B

 1 <html>  
 2 <head>  
 3     <script type="text/javascript">  
 4         function steal() {  
 5             iframe = document.frames["steal"];  
 6             iframe.document.Submit("transfer");  
 7         }  
 8     </script>  
 9 </head>  
10 　　  
11 <body onload="steal()">  
12 <iframe name="steal" display="none">  
13     <form method="POST" name="transfer" action="http://www.myBank.com/Transfer.php">  
14 　　　　　<input type="hidden" name="toBankId" value="11">  
15 　　　　　<input type="hidden" name="money" value="1000">  
16 　  </form>  
17 </iframe>  
18 </body>  
19 </html>

修复方式：1验证码 2检测refer 3目前主流的做法是使用Token抵御CSRF攻击

XSS(跨站脚本)它允许恶意web用户将代码植入到提供给其它用户使用的页面中。比如这些代码包括HTML代码和客户端脚本.

当用户点击以上攻击者提供的URL时，index.php页面被植入脚本，页面源码如下：

1 <?php  
2 $name = $_GET[\'name\'];  
3 echo "Welcome $name<br>";  
4 echo \'<a href="http://www.cnblogs.com/bangerlee/">Click to Download</a>\';  
5 ?>

这时，当攻击者给出以下URL链接：

1 index.php?name=guest<script>alert(\'attacked\')</script>

当用户点击该链接时，将产生以下html代码，带\'attacked\'的告警提示框弹出：

1 Welcome guest  
2 <script>alert(\'attacked\')</script>  
3 <br>  
4 <a href=\'http://www.cnblogs.com/bangerlee/\'>Click to Download</a>

跨站脚本的过滤RemoveXss函数

 1 function RemoveXSS($val) {  
 2    // remove all non-printable characters. CR(0a) and LF(0b) and TAB(9) are allowed  
 3    // this prevents some character re-spacing such as <java\0script>  
 4    // note that you have to handle splits with \n, \r, and \t later since they *are* allowed in some inputs  
 5    $val = preg_replace(\'/([\x00-\x08,\x0b-\x0c,\x0e-\x19])/\', \'\', $val);  
 6    // straight replacements, the user should never need these since they\'re normal characters  
 7    // this prevents like <IMG SRC=@avascript:alert(\'XSS\')>  
 8    $search = \'abcdefghijklmnopqrstuvwxyz\';  
 9    $search .= \'ABCDEFGHIJKLMNOPQRSTUVWXYZ\';  
10    $search .= \'1234567890!@#$%^&*()\';  
11    $search .= \'~`";:?+/={}[]-_|\\'\\\';  
12    for ($i = 0; $i < strlen($search); $i++) {  
13       // ;? matches the ;, which is optional  
14       // 0{0,7} matches any padded zeros, which are optional and go up to 8 chars  
15   
16       // @ @ search for the hex values  
17       $val = preg_replace(\'/(&#[xX]0{0,8}\'.dechex(ord($search[$i])).\';?)/i\', $search[$i], $val); // with a ;  
18       // @ @ 0{0,7} matches \'0\' zero to seven times  
19       $val = preg_replace(\'/(&#0{0,8}\'.ord($search[$i]).\';?)/\', $search[$i], $val); // with a ;  
20    }  
21   
22    // now the only remaining whitespace attacks are \t, \n, and \r  
23    $ra1 = array(\'javascript\', \'vbscript\', \'expression\', \'applet\', \'meta\', \'xml\', \'blink\', \'link\', \'style\', \'script\', \'embed\', \'object\', \'iframe\', \'frame\', \'frameset\', \'ilayer\', \'layer\', \'bgsound\', \'title\', \'base\');  
24    $ra2 = array(\'onabort\', \'onactivate\', \'onafterprint\', \'onafterupdate\', \'onbeforeactivate\', \'onbeforecopy\', \'onbeforecut\', \'onbeforedeactivate\', \'onbeforeeditfocus\', \'onbeforepaste\', \'onbeforeprint\', \'onbeforeunload\', \'onbeforeupdate\', \'onblur\', \'onbounce\', \'oncellchange\', \'onchange\', \'onclick\', \'oncontextmenu\', \'oncontrolselect\', \'oncopy\', \'oncut\', \'ondataavailable\', \'ondatasetchanged\', \'ondatasetcomplete\', \'ondblclick\', \'ondeactivate\', \'ondrag\', \'ondragend\', \'ondragenter\', \'ondragleave\', \'ondragover\', \'ondragstart\', \'ondrop\', \'onerror\', \'onerrorupdate\', \'onfilterchange\', \'onfinish\', \'onfocus\', \'onfocusin\', \'onfocusout\', \'onhelp\', \'onkeydown\', \'onkeypress\', \'onkeyup\', \'onlayoutcomplete\', \'onload\', \'onlosecapture\', \'onmousedown\', \'onmouseenter\', \'onmouseleave\', \'onmousemove\', \'onmouseout\', \'onmouseover\', \'onmouseup\', \'onmousewheel\', \'onmove\', \'onmoveend\', \'onmovestart\', \'onpaste\', \'onpropertychange\', \'onreadystatechange\', \'onreset\', \'onresize\', \'onresizeend\', \'onresizestart\', \'onrowenter\', \'onrowexit\', \'onrowsdelete\', \'onrowsinserted\', \'onscroll\', \'onselect\', \'onselectionchange\', \'onselectstart\', \'onstart\', \'onstop\', \'onsubmit\', \'onunload\');  
25    $ra = array_merge($ra1, $ra2);  
26   
27    $found = true; // keep replacing as long as the previous round replaced something  
28    while ($found == true) {  
29       $val_before = $val;  
30       for ($i = 0; $i < sizeof($ra); $i++) {  
31          $pattern = \'/\';  
32          for ($j = 0; $j < strlen($ra[$i]); $j++) {  
33             if ($j > 0) {  
34                $pattern .= \'(\';  
35                $pattern .= \'(&#[xX]0{0,8}([9ab]);)\';  
36                $pattern .= \'|\';  
37                $pattern .= \'|(&#0{0,8}([9|10|13]);)\';  
38                $pattern .= \')*\';  
39             }  
40             $pattern .= $ra[$i][$j];  
41          }  
42          $pattern .= \'/i\';  
43          $replacement = substr($ra[$i], 0, 2).\'<x>\'.substr($ra[$i], 2); // add in <> to nerf the tag  
44          $val = preg_replace($pattern, $replacement, $val); // filter out the hex tags  
45          if ($val_before == $val) {  
46             // no replacements were made, so exit the loop  
47             $found = false;  
48          }  
49       }  
50    }  
51    return $val;  
52 }