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Web Application Security

An Introduction to DOM XSS

Document Object Model Based Cross-Site Scripting (DOM Based XSS) is a type of Cross-site Scripting where instead of the payloads being stored or reflected by the remote web server and appearing in the response HTML the payload is instead stored in the DOM and processed insecurely by JavaScript. For those unfamiliar with what the DOM is, a short and fairly untechnical overview is available here.

The impact, and exploitation of DOM-XSS, is essentially the same as reflected or stored however the detection is a little different, as you can’t simply check the server responses and build up a payload. For example if you’re using Burp Suite for testing Burp doesn’t parse or execute JavaScript and therefore it won’t be too much help there. (It will however look for DOM-XSS through static analysis and pick up on issues such as location.hash ending up in document.write).

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Web Application Security

SQL Injection: Basics and Defence

Structured Query Language (SQL) is used all over the web and is potentially vulnerable to an injection attack any time that user input is insecurely concatenated into a query. An injection attack allows an attacker to alter the logic of the query and the attack can lead to confidential data theft, website defacement, malware propagation and host/network compromise.

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Web Application Security

IDOR: Insecure Direct Object Reference

In my experience Insecure Direct Object Reference is one of the least well known vulnerabilities out there, but it’s a very simply issue to explain. It’s a vulnerability that generally leads to loss of confidential data but can result in the less of modification of data too.

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Web Application Security

XSS: Cross-site Scripting: Lesson 2, Contexts!

Sometimes when I’m chatting to security engineers and developers I hear them say that the only characters you need to encode (or strip) are < and >. This often comes around due to .Net’s security filter which restricts any alpha-character from appearing after a < character. This filter prevents a lot of XSS attacks but it’s definitely not complete.

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Web Application Security

XXE: XML External Entity Injection

Here’s a quick write-up on XXE, starting with how to detect the vulnerability and moving on to how to fix it! XXE is a vulnerability in the way that XML parses handle user input and if an attacker is able to enter arbitrary or crafted data into an XML parser they may be able to inject entities and this could leave to file disclosure, denial-of-service attacks or in rare cases – code execution!