I'm quite new here. I'm trying to make a blog/journal site that allows users to post their own journal. I'm still quite reluctant on making it because I am really afraid of malicious code injections.
So here's a sample code:
<?php
$test = "<b>blah</b>"; //User input from SQL
echo "$test";
?>
What will come out is just the word "blah" in bold right? What I was trying to achieve was to echo "<b>blah</b>" instead. I don't want people to put some PHP codes that can actually mess up my whole web page. Please keep in mind that the variable $test is actually a MYSQL query, so that variable will be needed as an example. I know you can do echo '$test'; but it just comes out as "$test" instead. I feel like pulling my hair out I can't figure it out yet.
The second solution I know of is the htmlspecialchars(); function, but I want the strings to display as what I typed, not the converted ones...
Is there any way I can do that?
I think the OP wants the HTML itself to be output to the page, and not have the tags stripped. To achieve this, you can run the string first through htmlentities()
$test = '<b>blah</b>';
echo htmlentities($test);
This will output:
<b>blah</b>
Which will render in the page as
<b>blah</b>
Echo don't execute PHP code from string. This is impossible and this is not security hole in your code.
You can use a template engine like Twig for exemple.
If htmlspecialchars(); is not the one you are looking for, try the header() option.
header('Content-type: text/plain');
When you are gonna give <b>Hi</b> to a browser, it will be displayed in Bold and not the text be returned. But you can try this way, outputting it inside a <textarea></textarea>.
Or the other way is to use htmlentities():
<?php
$test = "<b>blah</b>"; //User input from SQL
echo htmlentities("$test");
?>
Related
I have a settings page in my Wordpress Admin Panel where I save some HTML code(with some PHP code in it) as a Wordpress Option, using update_option.
In phpmyadmin, the value is stored exactly like this:
<img src = \"<?php bloginfo(\'template_directory\'); ?>/images/flexslider/phone.png\">
It works perfect until I try to actually make the code work in a page. I'm printing it like this:
<?php echo urldecode(get_option('wp_slider_code')); ?>
This, unfortunately, prints the PHP code as it was HTML code. So the PHP code doesn't actually get executed; it's treated like a text, the url becoming:
<?php bloginfo('template_directory'); ?>/images/flexslider/phone.png
What can I do to make this PHP code get executed when I echo it on a page?
You have to use the eval() built-in function:
eval( $YourString );
(Edit:) If $YourString return a result, to cath the result you have to use:
$result = eval( $YourString );
Please note:
Caution
The eval() language construct is very dangerous because it allows execution of arbitrary PHP code. Its use thus is discouraged. If you have carefully verified that there is no other option than to use this construct, pay special attention not to pass any user provided data into it without properly validating it beforehand.
Read mor on PHP Documentation.
What happen if i use the following?
<?php echo "<?php echo date('Y'); ?>"; ?>
i could not find an answer anywhere, and when i try it myself, i get:
<?php echo date('Y'); ?></td></tr></table>
However, it does not show up on front browser, only source.
So my question is, does this affect the html/browser/server in any way?
as i do not want to end up creating a security issue should user post their
own php code in a html only format, like a bio page etc.
It's because of the chevrons ('<' and '>'), because the browser interprets them as tags.
There are 2 ways you could get round this.
Either use the codes for special characters, so you would do:
<?php echo "<?php echo date('Y'); ?>"; ?>
Or, an easier way, use the htmlspecialchars() function:
<?php echo htmlspecialchars("<?php echo 'hi'; ?>"); ?>
More info on the htmlspecialchars() function can be found at http://www.php.net//manual/en/function.htmlspecialchars.php
It is not a security problem and will not have any effects on browser or server, at least not because of PHP code. Even if the string contains PHP code it will just be sent to the client which will not attempt to execute it.
The real problem when echoing user-defined HTML is the risk of attacks such as XSS. Users could include arbitrary scripts or images or scramble the rest of the page by inserting arbitrary tags. In other words: Users could modify the whole page with a single line of HTML.
In general, it's a bad practice to allow such arbitrary input. Have a look at strip_tags which provides a very basic level of protection.
One guy tried to exploit it using this script
http://www.searchr.us/web-search.phtml?search=%22%3E%3Cscript%3Ealert%28String.fromCharCode%2872%29+String.fromCharCode%28105%29%29;%3C/script%3E
How do i stop it ?
And he also said that it is vulnerable to XSS and LPI...Please help me stop it.
Thanking You,
You need to HTML-encode all user-entered data that you output, including the user's search string.
To be safe, HTML-encode all values that are not explicitly meant to be HTML code.
The quick solution is to:
<?php echo htmlspecialchars($blah); ?>
instead of
<?php echo $blah; ?>
The long solution is to read a book on web site security.
Seeing as how that is a search query string, I'm guessing you're pulling the value directly from the query string and re-displaying it to the user?
Something along the lines of "Your search of 'something' returned 0 results"?
You need to encode any user entered data before displaying it.
I made a GET form recently.But the problem is that it is highly vulnerable.You can inject your an script as below.
http://mysite.com/processget.phtml?search=Hacked
I'm able to inject any kind of script into my above URL.I'm actually echoing my GET data using an echo in my BODY,so whenever i enter a malicious script it is being executed in my BODY tag.So now how do i limit this http://mysite.com/processget.phtml?search= to just Number,letters and a few symbols which i want.
For ex.The user should only be able to enter
http://mysite.com/processget.phtml?search=A123123+*$
So can anyof you help me fix this bug.I'm kind of new to PHP,so please explain.
if (!empty($_GET['search'])) {
$search = htmlentities($_GET['search'],ENT_QUOTES,'UTF-8');
echo $search;
}
Now it's safe.
But if you want to limit to specific symbols, then you need to use regular expressions.
You can let a user enter whatever you like; the key is to escape the output. Then the string is displayed as desired, rather than included as HTML.
Use a php function like htmlentities
Strip the tags:
echo strip_tags($_GET['search']);
Actually, you may want htmlspecialchars instead, which escapes the tags instead of removing them so they display as intended:
echo htmlspecialchars($_GET['search']);
I have a string that has HTML & PHP in it, when I pull the string from the database, it is echo'd to screen, but the PHP code doesn't display. The string looks like this:
$string = 'Hello <?php echo 'World';?>';
echo $string;
Output
Hello
Source Code
Hello <?php echo 'World';?>
When I look in the source code, I can see the php line there. So what I need to do is eval() just the php segment that is in the string.
One thing to consider is that the PHP could be located anywhere in the string at any given time.
* Just to clarify, my PHP config is correct, this is a case of some PHP being dumped from the database and not rendering, because I am echo'ing a variable with the PHP code in it, it fails to run. *
Thanks again for any help I may receive.
$str = "Hello
<?php echo 'World';?>";
$matches = array();
preg_match('/<\?php (.+) \?>/x', $str, $matches);
eval($matches[1]);
This will work, but like others have and will suggest, this is a terrible idea. Your application architecture should never revolve around storing code in the database.
Most simply, if you have pages that always need to display strings, store those strings in the database, not code to produce them. Real world data is more complicated than this, but must always be properly modelled in the database.
Edit: Would need adapting with preg_replace_callback to remove the source/interpolate correctly.
You shouldn't eval the php code, just run it. It's need to be php interpreter installed, and apache+php properly configured. Then this .php file should output Hello World.
Answer to the edit:
Use preg_replace_callback to get the php part, eval it, replace the input to the output, then echo it.
But. If you should eval things come from database, i'm almost sure, it's a design error.
eval() should work fine, as long as the code is proper PHP and ends with a semicolon. How about you strip off the php tag first, then eval it.
The following example was tested and works:
<?php
$db_result = "<?php echo 'World';?>";
$stripped_code = str_replace('?>', '', str_replace('<?php', '', $db_result));
eval($stripped_code);
?>
Just make sure that whatever you retrieve from the db has been properly sanitized first, since you're essentially allowing anyone who can get content into the db, to execute code.