I build web applications and I'm into web application security. I like to speak about secure development. My mission is to teach web developers how to build secure and fast web applications and why. (more about me, contact)

My trainings

And this is what they say about them: Originally, I've arranged Michal's training primarily for my colleagues because "of course I already know these things"... Michal has changed my mind in the first hour of the first day and continued to do so for the whole two days. Thanks to this training I finally understood some of the attack/defense concepts in full depth, and especially in the right context. — Jan Pospíšil, Senior PHP developer, Czech Radio

Public trainings

Come to my public trainings, everybody's welcome:

Trainings in Prague (or remote) are held regularly in the middle of March, June, September, and December, in other cities irregularly.

In-house trainings

Any public training can also be turned into an in-house training. As an extra, I offer these in-house-only courses:

Looking for Introduction to PHP, Classes and objects in PHP? I've handed them over to Martin Hujer. I've discontinued Web application performance, Martin Michálek runs a similar training.

My articles

Stealing session ids with phpinfo() and how to stop it

Stealing session ids from phpinfo() output has been a known technique for some time, and is used to bypass the HttpOnly attribute, which prohibits JavaScript from accessing a cookie marked as such (e.g. PHPSESSID). I just now thought of a solution that allows you to keep your phpinfo(): we'll simply censor the sensitive data, making phpinfo() lose some of its value to the attacker.

(read more…)

Origin, site, eTLD, eTLD+1, public suffix, PSL. What are they?
November 20, 2023

We call it pages, domains, servers, websites, internets and we hope the other party will understand. Maybe, maybe not, but that can always be cleared with the additional “wait, a server, don't you mean a website?” You can't just ask those questions when reading various specifications and technical documents, so they try to call things by their correct names and in a consistent manner. And they do it so well that terms like origin, site, same origin, same site, eTLD and public suffix are normally not even translated to other languages, because then nobody would understand it. And how does the attractiveness of subdomains relate to this?

(read more…)

Overriding HTTP response content in Chrome
October 5, 2023

The Chrome browser (and others like Edge) allows you to override both HTTP response headers and the response content. I've previously written about overriding the headers for testing purposes, let's see how you can override the body, or the content itself, as well. Starting with Chrome 117 (released in September 2023) it's also greatly simplified.

(read more…)

All articles

My talks


Upcoming talks

…at your event or conference, let me know!


Moderní problémy vyžadují moderní řešení Czech
October 8, 2023, LinuxDays 2023 (50 minutes)

DOM XSS and Trusted Types
May 11, 2023, OWASP Czech Chapter Meeting (60 minutes)

Co zajímá Špačka na nových verzích PHP? Czech
October 6, 2022, 51. sraz přátel PHP v Praze v CareCloudu (15 minutes)

Každej den je pátek, dejte mi od deployování svátek Czech
June 3, 2022, PHP live 2022 (40 minutes)

Jak princezna finálně zatočila s (DOM) XSS Czech
February 17, 2022, JSDays 2022 (60 minutes)

All talks

Me answering questions

CZ Podcast 319 - O bezpečnosti, nových vlastnostech prohlížečů i Shoptetu
May 6, 2024, CZ Podcast

Michal Špaček: Před připojováním na veřejné Wi-Fi sítě už nevaruju
September 5, 2022, Lupa.cz

O temné straně UX designu
March 1, 2022, BlueGhost Update

Bezpečnost na internetu
February 2, 2021, Jak na sítě

Grading How Companies (In)Securely Store Passwords
August 1, 2019, All Things Auth Podcast

All interviews