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Pádraic Brady:
20 Point List For Preventing Cross-Site Scripting In PHP
April 23, 2013 @ 09:27:02

Pádraic Brady has posted a 20 point list that wants to help you prevent cross-site scripting (XSS) issues in your applications.

Summarising knowledge has as much value as writing a 200 page treatise on a topic, so here is a list of 20 brief points you should bear in mind when battling Cross-Site Scripting (XSS) in PHP. Minus my usual book length brain fart . Chances are good that ignoring or acting contrary to any one of these will lead to a potential XSS vulnerability. It's not necessarily a complete list - if you think something needs to be added, let everyone know in the comments.

His tips include things like:

  • Never pass data from untrusted origins into output without either escaping or sanitising it.
  • Remember that anything not explicitly defined in source code has an untrusted origin.
  • Always include ENT_QUOTES, ENT_SUBSTITUTE and a valid character encoding when calling htmlspecialchars().
  • Use rawurlencode() to escape strings being inserted into URLs and then HTML escape the entire URL.
  • Validate all complete URLs if constructed from untrusted data.
  • Remember that HTMLPurifier is the only HTML sanitiser worth using.
  • Ensure that cookies which must only be transmitted over HTTPS are marked Secure.

He points out that XSS is still one of the most "popular" (and easy to exploit) attack methods out there, so keep these tips in mind when writing up your code.

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Link: http://blog.astrumfutura.com/2013/04/20-point-list-for-preventing-cross-site-scripting-in-php

Henrik Bjørnskov's Blog:
Symfony2 Add Cross Site Request Forgery protection to login forms
December 30, 2011 @ 10:28:42

In a new post to his blog Henrik Bjørnskov has a tip on preventing cross-site request forgeries in your Symfony2 forms with the help of a simple Symfony2 configuration setting.

When talking with @jmikola on #Symfony-dev this afternoon we got into the subject of cross site request forgery and symfony2 login forms. And it seems that form-login already supports this but neither of us knew how it worked. So here is another quick tip. This time about securing you login form from cross site attacks.

The key is to define a "csrf_provider" in your security.yml config file and point it to the "form.csrf_provider" provider. He also includes the controller and view code/templating you'll need to get the token included in the form (and validated).

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PHPMaster.com:
Preventing Cross-Site Request Forgeries
September 28, 2011 @ 10:12:11

SitePoint' PHPMaster.com has a new tutorial posted today from Martin Psinas about some tactics to prevent cross-site request forgeries from happening in your PHP application. The article introduces key concepts of CSRF and how you can keep it from happening in your code.

Cross-site request forgery (CSRF) is a common and serious exploit where a user is tricked into performing an action he didn't explicitly intend to do. This can happen when, for example, the user is logged in to one of his favorite websites and proceeds to click a seemingly harmless link. In the background, his profile information is silently updated with an attacker's e-mail address. [...] Any action that a user is allowed to perform while logged in to a website, an attacker can perform on his/her behalf, whether it's updating a profile, adding items to a shopping cart, posting messages on a forum, or practically anything else.

He shows it to you "in action" with a PHP script for a basic login page that takes a username and password, does some filtering and sets the username to the session. Their "harmless.html" file offers a link to the site's "process" page with a logout action that would allow the "harmless" file access to the current session if clicked. To prevent this from happening, they suggest a unique token be included in interactions on your site. This key is checked against a token in the current session (or other location) and is only valid if they match.

The Symfony framework has included this as a part of their forms for a while now and includes automatic handling to check its validity. Solutions also exist for other frameworks like Zend Framework and many others.

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Paul Reinheimer's Blog:
Stop Messing up CSRF Protection
November 10, 2008 @ 08:47:53

In his latest post Paul Reinheimer looks at cross-site request forgeries and, despite the best efforts of the PHP security community, how developers still just miss the point in protecting their own code.

So, cross site request forgeries are a pretty common topic these days; they're in almost every security talk, book, site etc. This is okay; they're important [...] Most of the sites, and all of the books I've read demonstrate things correctly, but when it comes to actual implementation, time and time again, I see code that's just wrong.

He looks at two of the "essentials" when it comes to protecting you and your application - comparison (not taking other values of variables into account) and the unpredictable token (not making tokens, like md5 hashes of information, random enough).

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Jani Hartikainen's Blog:
How to CSRF protect all your forms
October 16, 2008 @ 12:07:26

Jani Hartikainen has posted a few ideas on cross site request forgeries in a new blog entry, including some methods to help prevent it in your application.

CSRF, or Cross-Site Request Forgery, is a vulnerability very common in websites. [...] This can be dangerous, especially if your admin interface is compromised: There may be a button on the other site which goes to your admin interface and deletes the latest blogpost for example - and you wouldn't want that!

His method is a three-step process for protection - use POST, protect against cross-site scripting and use a CSRF key in the form to help prevent abuse. A simple script is included to show it working and is adapted to work in a controller plugin for the Zend Framework.

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Secubos.com:
Cross-Site Scripting Vulnerability in phpFaber
October 31, 2006 @ 11:17:00

A cross-site scripting bug has been announced on the Secuobs.com website for the phpFaber content management system.

Vigilon has reported a vulnerability in phpFaber CMS, which can be exploited by malicious people to conduct cross-site scripting attacks.

Input passed via the URL in cms_images/js/htmlarea/htmlarea.php is not properly sanitised before being returned to the user. This can be exploited to execute arbitrary HTML and script code in a user's browser session in context of an affected site.

For complete information on the issue, check out this report.

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