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Jan Reilink

My name is Jan. I am not a hacker, coder, developer or guru. I am merely a systems administrator, doing my daily thing at Vevida.

Binary webshell through OPcache in PHP 7

GoSecure wrote up a new PHP exploitation technique using the default OPcache engine from PHP 7. Using this attack vector, it’s possible to bypass certain hardening techniques that disallow the file write access in the web directory. This could be used by an attacker to execute his own malicious code in a hardened environment.


This new PHP 7 OPcache attack vector is an additional exploitation technique tailored to specific hardened environments. It is not a universal vulnerability affecting PHP applications. With the arrival of PHP 7.0 in major distributions such as Ubuntu 16.04, this attack vector reinforces even more the need to audit your code for file upload vulnerabilities and to be wary of potentially dangerous server configuration.

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Windows Update error 0xc1420127 and 0xc190010b when upgrading Windows 8.1 to Windows 10

Last weekend I had to update my girlfriends laptop from Windows 8.1 to Windows 10. Some might say, an easy task. Well, it wasn’t. After downloading the Windows 10 update through Windows Update, Windows Update returned errors 0xc1420127 and 0xc190010b, even using the Windows 10 media creation tool. And as always there are many reasons for these errors. In this short post, I’ll provide some possible solutions and tips.

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How to install Microsoft’s SQL Server Driver for PHP

In this article I’ll show you how to install the Microsoft SQL Server Driver for PHP 7+. This makes the use of an SQL Server database back-end for your PHP website easy. If you want to communicatie with SQL Server using PHP you need to rely on some additional software and PHP extensions. This post walks you through the steps necessary to install the SQL Server driver and SQLSRV extension for PHP 7+, on Windows Server IIS of course.

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Optimize WordPress MySQL tables through Cron, behind the scenes

Schedule WordPress database optimization with WP-Cron

To regularly optimize my WordPress database tables, I created a small plugin that utilizes the WordPress Cron feature. This comes in handy to perform database optimization for WordPress on a regular basis, without forgetting about it. Just activate and enjoy. And here is the plugin code …

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Cracking PHP rand()

Sjoerd Langkemper writes about Cracking PHP rand(): Webapps occasionaly need to create tokens that are hard to guess. For example for session tokens or CSRF tokens, or in forgot password functionality where you get a token mailed to reset your password. These tokens should be cryptographically secure, but are often made by calling rand() multiple times and transforming the output to a string. This post will explore how hard it is to predict a token made with rand().


This is a very interesting read about how PHP rand() works, and how to attack & crack it. The post ends with the following conclusion:

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Deny vulnerable WordPress plugins using Windows Server File Server Resource Manager’s File Screens

Using Windows Server File Server Resource Manager‘s File Screens you can block vulnerable WordPress plugins from being uploaded to your IIS web server. In the following example, you’ll learn how to block WP DB Backup plugin system-wide on Windows Server, read on…

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Install Varnish Cache on CentOS 6.7

In this article I’ll show you how to install Varnish Cache on CentOS, version 6.7 in this case. Varnish is a web application accelerator also known as a caching HTTP reverse proxy. You install it in front of any server that speaks HTTP and configure it to cache the contents. Because Varnish Cache is really, really fast, web applications like WordPress, Drupal and Joomla can greatly benefit from Varnish Cache.

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