JWT (JSON Web Token) (in)security

JWT (JSON Web Token) is a mechanism that is often used in REST APIs it can be found in popular standards, such as OpenID Connect, but we will also encounter it sometimes using OAuth2. It is used both in large companies and smaller organisations. There are many libraries available that support JWT, and the standard …

Write-up of DOMPurify 2.0.0 bypass using mutation XSS

Yesterday, a new version of DOMPurify (very popular XSS sanitization library) was released, that fixed a bypass reported by us. In this post I’ll show how exactly the bypass looked like preceded by general information about DOMPurify and how it works. If you are aware of how purifiers work and what mXSS is – you …

Security analysis of <portal> element

Portal is a fairly new HTML element that is currently supported only in Chrome Canary behind the #enable-portals flag. Their main objective is to enable seamless transitions to the web by pre-rendering content in an iframe-like element that can be then “promoted” (activated) to a top-level frame. In this article we focus of security analysis thereof.

HTTP 2 protocol – it is faster, but is it also safer?

Do we want the current web applications to run faster without additional expenditures on better network connection or server infrastructure? Yes, of course, and that was the main goal for the developers of the HTTP/2 protocol. To be more precise, it was about increasing the efficiency of communication between the client (in other words, the …

Basics of HTTP Protocol

Introduction HTTP headers, URLs, URIs, requests, responses, percentage encodings, HTML forms, parameters sent by the HTTP protocol, various HTTP server implementations resulting in security problems – these are just a few elements that I will address in this text. The beginner readers will learn the necessary basics to further explore the subject of web applications …