willem.com

Cyber Security on Willem's Blog

Traffic shaping using iptables and tc

Limiting outbound network bandwidth per client IP-address

Apr. 1, 2020
This month I responded to an automated alert indicating excessive bandwidth usage on a server, requiring me to apply traffic shaping to mitigate the traffic.

Last month I received an automated alert indicating excessive bandwidth usage, usually a sign of trouble. When this happens, you should follow a standard incident procedure, trying to isolate the source of the traffic before shutting it down. The cause of this incident was not what I expected however... requiring a different kind of mitigation than a simple blockade.

Visiting an international hackers conference

OWASP Global AppSec Amsterdam

Sep. 27, 2019
This month I attended Global AppSec Amsterdam, an international conference for hackers and security specialists. Read along for some of the highlights.

This month I was lucky enough to attend Global AppSec Amsterdam, an international conference for hackers and security specialists. There were presentations from former intelligence agents, bounty hunters, academics and software vendors. I learned about some of the newest hacking techniques, met with interesting people and played some cool retro games. Read along for more.

Fighting backscatter spam at server level

Configure Postfix to block spam before it enters the server

Sep. 10, 2019
Deal with backscatter spam by implementing a stringent SMTP delivery policy at MTA level.

This month I had to deal with backscatter spam, affecting one of the mail servers I manage. As server engineer I make sure that servers don't send spam and that incoming email gets filtered. Despite all good efforts, this server kept being blacklisted for sending spam to iCloud, Office 365 and Google Gmail for Business (G Suite). Read along to find out how what caused this and how to fix this.

Dig for dummies

Explaining an highly useful network tool

May 24, 2019
Learn how to use the dig command to query domain name servers to find the source of network problems, IP-addresses, hostnames, mail servers and related info.

When you're building websites, apps or email services you may run into domain names and their configurations. When everything is working as it should, most of this is invisible. But when troubleshooting a domain name configuration, it may be necessary to dig a little deeper... read along to learn how!

Search like a pro: Google search operators

Comprehensive list of advanced search operators

Apr. 25, 2019
Read along for a comprehensive list of advanced Google search operators that allow you to filter your search results.

You probably use the world's most famous search engine to find things everyday, but you might not know about some of its advanced search operators. You can use these special search phrases to find things that are otherwise burried in the search results. Read along for a comprehensive list of advanced Google search operators.

WordPress: 10 tips to secure your website

Keep hackers out of the world's most popular content management system

Mar. 31, 2019
A lot of people use WordPress to manage their website. Prevent your site from being hacked using this blog post.

A lot of people use WordPress to manage their website, therefore it's no surprise people ask me to have a look at their site's security. As ethical hacker, I encounter WordPress in different shapes, sizes and states. Some of them are really badly protected against hacks. Prevent your site from being hacked using these 10 practical tips.

Understanding the security concerns in shared hosting

Considering open ports and unused network facing services

Feb. 28, 2019
People pay me to hack them, provided I'll explain how I did it. Read along to learn how hackers use security holes to hack your app, webshop or website!

People pay me to hack them, provided I'll explain how it was done, so future hacks can be prevented. As security consultant, I scan for weaknesses in my clients' apps, webshops and websites. Very often a hack starts by exploiting a security hole that is visible remotely. Read along to learn how hackers find security holes and what you can do to secure them.

Cyber security: 5 easy tips to protect your server against hackers

Server hardening best practices for Windows and Linux

Mar. 10, 2018
These 5 practical cyber security measures will improve the safety of server, website and data.

This week one of my clients was hacked and asked me for emergency assistance to help secure their server infrastructure. It was a web server that ran WordPress websites on Apache (with PHP/MySQL), including a few webshops with customer data. This hack could easily have been prevented with the following best practices, is your server secure?

All blog posts
It's pretty hard hacking into my WP-Admin page because you cannot find it (hint: it's not at /wp-admin)
It's pretty hard hacking into my WP-Admin page because you cannot find it (hint: it's not at /wp-admin)
Using tokens to control traffic - only passengers (or data packets) with a valid token are allowed. Tokens are returned as traffic reaches its destination.
Using tokens to control traffic - only passengers (or data packets) with a valid token are allowed. Tokens are returned as traffic reaches its destination.
Hacking Google - How I could have stolen your photos from Google (Gergö Turcsányi)
Hacking Google - How I could have stolen your photos from Google (Gergö Turcsányi)
Bandwidth graph of AMS-IX shows a predictable pattern - notice the wave-like pattern
Bandwidth graph of AMS-IX shows a predictable pattern - notice the wave-like pattern
James Kettle on hacking PayPal - gaining $38,900 in bounties
James Kettle on hacking PayPal - gaining $38,900 in bounties
Sniff WordPress password using WireShark packet capturing (via blog.wpscans.com)
Sniff WordPress password using WireShark packet capturing (via blog.wpscans.com)
Contagious effect of an hacked website (red indicating trouble)
Contagious effect of an hacked website (red indicating trouble)
Bandwidth graph with unusual spike indicating that something is wrong - you don't need to be Sherlock Holmes to find it
Bandwidth graph with unusual spike indicating that something is wrong - you don't need to be Sherlock Holmes to find it
Coffee and PONG on the video-sports console with CRT monitor
Coffee and PONG on the video-sports console with CRT monitor
Persistent Client-Side XSS is a real threat - by Marius Steffens and Ben Stock
Persistent Client-Side XSS is a real threat - by Marius Steffens and Ben Stock
Global AppSec Amsterdam
Global AppSec Amsterdam
Using dig to get information about the SPF-records for a domain name, google.com
Using dig to get information about the SPF-records for a domain name, google.com
Sample traffic shaping script
Sample traffic shaping script
Update WordPress from the wp-admin dashboard
Update WordPress from the wp-admin dashboard
Leaking personal user information from the WordPress REST API
Leaking personal user information from the WordPress REST API
Global AppSec-Amsterdam
Global AppSec-Amsterdam
Lessons learned from dealing with terrorists
Lessons learned from dealing with terrorists
Using dig to get information about a domain name, willem.com
Using dig to get information about a domain name, willem.com

More Cyber Security on Willem's Blog

All blog posts