How to fix cross site scripting in php
What is Cross-Site Scripting?Cross-Site Scripting (XSS) attacks are a form of injection attack, where malicious scripts are injected into trusted web applications. Show
XSS is usually inserted through a website using a hyperlink or a web form. The inserted code can be used via any client-side language such as JavaScript, PHP, HTML. A simple XSS attack will occur on a vulnerable website that accepts user input via a GET parameter and displays the data on the website. Let’s take a look at the URL example below:
This URL points to a website that reads the value for username from the An attacker may inject malicious code into the website by setting the value for u to the following:
The injected script will produce a JavaScript dialog pop-up alert stating “Your website is compromised!” Whilst this may appear trivial, attackers can use this process to send the unassuming user to a site they control. To learn about different types of XSS attacks check out this blog. Understanding how XSS attacks work in PHP applications is important so they can be prevented as part of the development pipeline before they hit production and be secure by design. In this article:
How does XSS in PHP work?As a developer with access to the source code, you can embed standard PHP code in a blade file for example, if you are coding in Laravel Framework. XSS PHP ExampleThis example looks at a website that displays specific data to users based on the group they belong to. The current group is specified via GET parameter in the URL. Using standard PHP inside a blade file, this code will display a user’s group: Hello user, your current group is beginner [ ] The website displays the
value for the group parameter like this: And the URL for the page becomes
Injecting the following code into the URL enables an XSS attack:
The injected code will cause a redirect to maliciouswebsite.com as soon as the site loads. How to fix this XSS vulnerability Since a blade template renders the website, we can rewrite the code by replacing the standard PHP code with a blade function. The new code is shown below: Hello user, your current group is [ {{ $_GET['group'] }} ] The code above uses the {{ }} echo statement to escape the value of the group parameter. This causes the value to be rendered as plain text all the time. Some other good ways to prevent this kind of XSS attack are validating and sanitizing inputs from the user. At all times you should avoid displaying and processing the user data without checking the content source and credibility. Preventing XSS in PHPPreventing XSS in PHP has two main considerations:
There is no single sanitization method that can prevent all the XSS attempts no matter how well we filter the input. Required filtering is mostly dependent on the context in which data gets inserted. Preventing XSS with data inserted between HTML elements is the most efficient. On the other hand, preventing XSS with data inserted in Javascript code is much more complicated. Input Sanitization in PHPFor most PHP websites,
‘ You will notice that these do
not include single quotes. “ htmlentities() vs htmlspecialchars()
strip_tags()We do not recommend using addslashes()Function As you can see, Most engines running JavaScript will construct code segments from open and closed The browser will process this as the injected code is an entirely new code segment that contains valid JavaScript. When will entity encoding fail?As we described previously the location where the data gets inserted must be taken into consideration when preventing XSS in PHP. Let’s go over some examples where entity encoding with A simple and common example is when data gets inserted within the actual attribute or element tag. HTML Event Attributes allow for JavaScript to be called upon a
particular event. This may be a rare situation when extremely defined filtering is required, but nevertheless, the location where input gets inserted should always be taken into consideration when preventing XSS in PHP applications. Preventing XSS in PHP with BrightWhile traditional Dynamic Application Security Testing (DAST) tools can test for some XSS vulnerabilities, they are often limited and produce a large number of false-positive results. Bright can automatically crawl your applications regardless of the programming language used, to test for a wide range of vulnerabilities including XSS, giving you maximum coverage, seamlessly integrated across development pipelines. Engineering and security teams can trust Bright’s results, with automatic validation of every XSS finding carried out, with NO/false positives. Bright even generates a screenshot proof of concept along with comprehensive developer-friendly remediation advice to fix the issue quickly and early. Start testing with Bright scanner today – get a free account Which PHP function can help prevent crossUsing htmlspecialchars() function – The htmlspecialchars() function converts special characters to HTML entities. For a majority of web-apps, we can use this method and this is one of the most popular methods to prevent XSS.
How can XSS be prevented?In general, effectively preventing XSS vulnerabilities is likely to involve a combination of the following measures: Filter input on arrival. At the point where user input is received, filter as strictly as possible based on what is expected or valid input. Encode data on output.
What is crossCross-Site Scripting (XSS) attacks are a form of injection attack, where malicious scripts are injected into trusted web applications. XSS is usually inserted through a website using a hyperlink or a web form. The inserted code can be used via any client-side language such as JavaScript, PHP, HTML.
Is Htmlentities enough to prevent XSS?In answer to your question, you should use htmlentities() when outputting any content that could contain user input or special characters. Show activity on this post. htmlspecialchars() is more than enough. htmlentities is for different use, not preventing XSS.
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