XPATH.md

XPath Injection

The code below is vulnureable to XPath Injection

const xpath = require('xpath');
const dom = require('xmldom').DOMParser;

// Parse the user-provided XML data
const xmlData = new dom().parseFromString(req.body.xmlData);

// Use the user-provided value as a parameter in the select() method
const nodes = xpath.select(req.body.xpathExpression, xmlData);

// Do something with the selected nodes
console.log(nodes);

Why it's vulnerable?

This code uses the xpath and xmldom libraries to parse an XML document provided by the user in an HTTP request, and then use an XPath expression to select nodes from the document. However, if the user supplies a malicious XPath expression, they can modify the selection to include arbitrary nodes from the document.

Impact?

For example, if the user supplies the following XPath expression in the request:

xpathExpression: '//*[name()="secret" or name()="password"]'

The xpath.select() method will select all nodes with a name of secret or password from the document, allowing the attacker to retrieve sensitive information from the XML data.

How to fix?

To prevent this type of attack, it's important to properly validate and sanitize user-provided input before using it in an XPath expression. In this case, you could use a regular expression to ensure that the XPath expression only contains allowed characters, such as letters, numbers, and common XPath operators:

const xpath = require('xpath');
const dom = require('xmldom').DOMParser;

// Parse the user-provided XML data
const xmlData = new dom().parseFromString(req.body.xmlData);

// Validate the XPath expression using a regular expression
const xpathRegex = /^[a-zA-Z0-9\s\/\.\@\*\[\]\=]+$/;
if (!xpathRegex.test(req.body.xpathExpression)) {
  // The XPath expression is invalid, return an error
  return res.status(400).send('Invalid XPath expression');
}