XXE Injection Attacks – XML External Entity Vulnerability With Examples


XXE Injection Attacks or XML External Entity vulnerabilities are a specific type of Server Side Request Forgery or SSRF attack relating to abusing features within XML parsers.

XXE Injection Attacks - XML External Entity Vulnerability With Examples

The features these attacks go after are widely available but rarely used and when trigged can cause a DoS (Denial of Service) attack and in some cases much more serious escalation like extraction of sensitive data or in worst case scenarios RCE or Remote Code Execution.

What is XML

In computing, Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable.

From: https://en.wikipedia.org/wiki/XML

It’s been replaced in a lot of modern APIs by JSON, but a lot of applications still use XML and/or have XML parsers inside so it’s good to be aware of XXE attacks as a vector.

XML parsers validate data in two main ways, XXE falls within the DTD or Data Type Definition method.

What is an XXE Attack

The thing is the XML entities can be defined anywhere, including externally, this is where XXE comes in and can be abused by an attacker by using XML entities to request the execution of certain files or even to return the contents of files if they know the structure of your web application for example.

It’s also worth mentioning, that with some XML parsers, it’s even possible to get directory listings in addition to the contents of a file.

XXE Attack Example

An example would look like this:

Request

Response

Obviously this is a simple example, but it could be used to echo /etc/passwd, get secrets from source code repos or execute malicious code (like a web shell) if the attacker has managed to upload something.

You can find out more, in much more depth, here:

Part 1 – What is XML External Entity (XXE)?
Part 2 – XML External Entity (XXE) limitations
Part 3 – Out-of-band XML External Entity (OOB-XXE)

Posted in: Exploits/Vulnerabilities

,


Latest Posts:


Socialscan - Command-Line Tool To Check For Email And Social Media Username Usage Socialscan – Command-Line Tool To Check For Email And Social Media Username Usage
socialscan is an accurate command-line tool to check For email and social media username usage on online platforms, given an email address or username,
CFRipper - CloudFormation Security Scanning & Audit Tool CFRipper – CloudFormation Security Scanning & Audit Tool
CFRipper is a Python-based Library and CLI security analyzer that functions as an AWS CloudFormation security scanning and audit tool
CredNinja - Test Credential Validity of Dumped Credentials or Hashes CredNinja – Test Credential Validity of Dumped Credentials or Hashes
CredNinja is a tool to quickly test credential validity of dumped credentials (or hashes) across an entire network or domain very efficiently.
assetfinder - Find Related Domains and Subdomains assetfinder – Find Related Domains and Subdomains
assetfinder is a Go-based tool to find related domains and subdomains that are related to a given domain from a variety of sources including Facebook and more.
Karkinos - Beginner Friendly Penetration Testing Tool Karkinos – Beginner Friendly Penetration Testing Tool
Karkinos is a light-weight Beginner Friendly Penetration Testing Tool, which is basically a 'Swiss Army Knife' for pen-testing and/or hacking CTF's.
Aclpwn.Py - Exploit ACL Based Privilege Escalation Paths in Active Directory Aclpwn.Py – Exploit ACL Based Privilege Escalation Paths in Active Directory
Aclpwn.py is a tool that interacts with BloodHound< to identify and exploit ACL based privilege escalation paths.


Comments are closed.