CodeQL documentation

XPath injection

ID: js/xpath-injection
Kind: path-problem
Severity: error
Precision: high
Tags:
   - security
   - external/cwe/cwe-643
Query suites:
   - javascript-code-scanning.qls
   - javascript-security-extended.qls
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

If an XPath expression is built using string concatenation, and the components of the concatenation include user input, it makes it very easy for a user to create a malicious XPath expression.

Recommendation

If user input must be included in an XPath expression, either sanitize the data or use variable references to safely embed it without altering the structure of the expression.

Example

In this example, the code accepts a user name specified by the user, and uses this unvalidated and unsanitized value in an XPath expression constructed using the xpath package. This is vulnerable to the user providing special characters or string sequences that change the meaning of the XPath expression to search for different values.

const express = require('express');
const xpath = require('xpath');
const app = express();

app.get('/some/route', function(req, res) {
  let userName = req.param("userName");

  // BAD: Use user-provided data directly in an XPath expression
  let badXPathExpr = xpath.parse("//users/user[login/text()='" + userName + "']/home_dir/text()");
  badXPathExpr.select({
    node: root
  });
});

Instead, embed the user input using the variable replacement mechanism offered by xpath:

const express = require('express');
const xpath = require('xpath');
const app = express();

app.get('/some/route', function(req, res) {
  let userName = req.param("userName");

  // GOOD: Embed user-provided data using variables
  let goodXPathExpr = xpath.parse("//users/user[login/text()=$userName]/home_dir/text()");
  goodXPathExpr.select({
    node: root,
    variables: { userName: userName }
  });
});

References