Think SECURITY when processing PHP. forms!
These pages will show how lớn process PHPhường forms with security in mind. Proper validation of khung data is important khổng lồ protect your khung from hackers và spammers!
The HTML khung we will be working at in these chapters, contains various input fields: required và optional text fields, radio buttons, và a submit button:
The validation rules for the form above sầu are as follows:
Field Validation Rules Name Required. + Must only contain letters & whitespace E-mail Required. + Must contain a valid gmail address (with& .) Website Optional. If present, it must contain a valid URL Comment Optional. Multi-line đầu vào field (textarea) Gender Required. Must select one
First we will look at the plain HTML code for the form:
Text Fields
The name, tin nhắn, and website fields are text đầu vào elements, và the phản hồi field is a textarea. The HTML code looks like this:
Name: <đầu vào type="text" name="name"> E-mail: <đầu vào type="text" name="email">Website: Comment:
Gender:Female<đầu vào type="radio" name="gender" value="male">MaleOther
What is the $_SERVER<"PHP_SELF"> variable?The $_SERVER<"PHP_SELF"> is a super global variable that returns the filename of the currently executing script.
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So, the $_SERVER<"PHP_SELF"> sends the submitted form data lớn the page itself, instead of jumping to a different page. This way, the user will get error messages on the same page as the form.
What is the htmlspecialchars() function? The htmlspecialchars() function converts special characters lớn HTML entities. This means that it will replace HTML characters like < and > with < & >. This prevents attackers from exploiting the code by injecting HTML or Javascript code (Cross-site Scripting attacks) in forms.
Big Note on PHP Form Security
The $_SERVER<"PHP_SELF"> variable can be used by hackers!
If PHP_SELF is used in your page then a user can enter a slash (/) & then some Cross Site Scripting (XSS) commands to lớn exedễ thương.
Cross-site scripting (XSS) is a type of computer security vulnerability typically found in Web applications. XSS enables attackers lớn inject client-side script into Web pages viewed by other users.
Now, if a user enters the normal URL in the address bar lượt thích "http://www.example.com/test_khung.php", the above sầu code will be translated to:
This code adds a script tag and an alert command. And when the page loads, the JavaScript code will be executed (the user will see an alert box). This is just a simple and harmless example how the PHP_SELF variable can be exploited.
Be aware of that any JavaScript code can be added inside the
- this would not be executed, because it would be saved as HTML escaped code, like this:
<script>location.href("http://www.hacked.com")</script>
The code is now safe lớn be displayed on a page or inside an e-mail.
We will also vị two more things when the user submits the form:
Strip unnecessary characters (extra space, tab, newline) from the user input data (with the PHP trim() function) Remove backslashes () from the user input data (with the PHP stripslashes() function)The next step is lớn create a function that will vì chưng all the checking for us (which is much more convenient than writing the same code over & over again).
We will name the function test_input().
Now, we can kiểm tra each $_POST variable with the test_input() function, & the script looks like this:
Example
== "POST") function test_input($data) ?>
Try it Yourself »
Notice that at the start of the script, we kiểm tra whether the khung has been submitted using $_SERVER<"REQUEST_METHOD">. If the REQUEST_METHOD is POST, then the size has been submitted - & it should be validated. If it has not been submitted, skip the validation và display a blank form.
However, in the example above, all input fields are optional. The script works fine even if the user does not enter any data.
The next step is lớn make đầu vào fields required & create error messages if needed.
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