CWE-91 XML Injection

Description

XML Injection

Reference: https://cwe.mitre.org/data/definitions/91.html

OWASP Category: A03:2021 – Injection

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Vulnerable Pattern

❌ Example 1: Vulnerable Pattern

// VULNERABLE: User input directly in XML
String xml = "<user><name>" + userName + "</name></user>";

Why it's vulnerable: This pattern is vulnerable to XML Injection

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Deterministic Fix

✅ Secure Implementation: Secure Implementation

// SECURE: Use XML library or escape special characters
import org.apache.commons.text.StringEscapeUtils;
String safeName = StringEscapeUtils.escapeXml11(userName);
String xml = "<user><name>" + safeName + "</name></user>";

// Better: Use JAXB or DOM API
DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
Document doc = builder.newDocument();
Element root = doc.createElement("user");
Element name = doc.createElement("name");
name.setTextContent(userName); // Auto-escapes
root.appendChild(name);

Why it's secure: Implements proper protection against XML Injection

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Detection Pattern

Look for these patterns in your codebase:

# Find XML string concatenation
grep -rn "\"<.*>\".*+" --include="*.java" | grep -v "//"

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Remediation Steps

1. Use XML libraries that auto-escape content (JAXB, DOM)

2. Escape XML special characters (<>&"') in user input

3. Use setTextContent() instead of string concatenation

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Key Imports

import org.apache.commons.text.StringEscapeUtils;

import javax.xml.parsers.DocumentBuilder;

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Verification

After remediation:

• Run SAST scanner to confirm vulnerability is resolved

• Review all instances of the vulnerable pattern

• Add unit tests that verify the secure implementation

• Check for similar patterns in related code

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Trigger Examples

Fix CWE-91 vulnerability
Resolve XML Injection issue
Secure this Java code against xml injection
SAST reports CWE-91

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Common Vulnerable Locations

| Layer | Files | Patterns | |-------|-------|----------|

| Controller | *Controller.java | User input handling |

| Service | *Service.java | Business logic |

| Repository | *Repository.java | Data access |

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References

• CWE-91: XML Injection

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Source: Generated by Java CWE Security Skills Generator Last Updated: 2026-03-07