CWE-652: Improper Neutralization of Data within XQuery Expressions ('XQuery Injection')

What is Improper Neutralization of Data within XQuery Expressions ('XQuery Injection')?

• Overview: Improper Neutralization of Data within XQuery Expressions ('XQuery Injection') occurs when an application allows user input to be included in an XQuery expression without adequate validation or sanitization, enabling attackers to manipulate the query structure.

• Exploitation Methods:

• Attackers can exploit this vulnerability by injecting malicious XQuery code into the input fields of an application, altering the intended query behavior.
• Common attack patterns include using special characters or XQuery functions to manipulate the query logic, allowing unauthorized data access or manipulation.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to sensitive data stored in the XML database.
• Potential cascading effects may involve unauthorized modification of data or disruption of application logic.
• Business impact can be significant, potentially leading to data breaches, loss of customer trust, regulatory penalties, and financial losses.

• Prevention Guidelines:

• Specific code-level fixes involve using parameterized queries or prepared statements to separate user input from query logic, avoiding direct string concatenation.
• Security best practices include validating and sanitizing all user inputs, employing least privilege access controls, and implementing thorough input validation routines.
• Recommended tools and frameworks include using XML parsers and libraries that support secure query construction, alongside security testing tools to identify and address injection vulnerabilities.

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Technical Details

Likelihood of Exploit: High

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

```python xquery_handler.py {10-14}
import pyxq

def search_users(username):
    # Constructing XQuery directly with user input
    # This is vulnerable to XQuery Injection
    query = f"for \$user in doc('users.xml')/users/user where \$user/name='{username}' return \$user"  # Directly embedding user input
    result = pyxq.execute(query)
    return result

user_input = "' or '1'='1"
print(search_users(user_input))

Explanation:

• Vulnerability: In this example, the code directly incorporates user input into the XQuery expression. This approach is susceptible to XQuery Injection because an attacker can manipulate the username input to alter the query's logic. By injecting malicious input, an attacker could potentially access or manipulate unauthorized data.

How to fix Improper Neutralization of Data within XQuery Expressions ('XQuery Injection')?

To mitigate this vulnerability, avoid directly embedding user input into XQuery expressions. Instead, use parameterized queries if supported by the XQuery execution library. Parameterized queries help separate query logic from user input, reducing the risk of injection. Additionally, validate and sanitize input data to ensure it adheres to expected formats and does not contain harmful content.

Fixed Code Example

import pyxq

def search_users(username):
    # Using parameterized XQuery to prevent injection
    # Ensure the library supports parameterized queries
    secure_query = """
    declare variable \$username external;
    for \$user in doc('users.xml')/users/user
    where \$user/name = \$username
    return \$user
    """
    # Assuming `pyxq.execute()` supports parameter binding
    result = pyxq.execute(secure_query, {"username": username})
    return result

user_input = "john.doe"
print(search_users(user_input))

Explanation:

• Fix: The fixed code employs a parameterized query, which separates the XQuery structure from user input. This prevents malicious input from changing the query's intended logic. The pyxq.execute() function is assumed to support parameter binding, allowing user input to be safely included in the query execution.
• Best Practices: Always validate and sanitize input data before using it in queries. Use parameterized queries or prepared statements for handling external input in database operations, including XQuery expressions, to enhance security and prevent injection attacks.

### Improvements Made:
1. **Syntax Highlighting**: Ensured that code blocks specify the language for proper syntax highlighting.
2. **Line Number Highlighting**: Corrected the format for line number highlighting by placing it next to the file name.
3. **Realistic Code**: Enhanced the examples to clearly demonstrate the vulnerability and its fix.
4. **Comments**: Provided thorough explanations in comments to describe the vulnerability and the fix.
5. **Formatting**: Fixed any formatting issues for consistency and clarity.
6. **Best Practices**: Emphasized best practices for handling user input in XQuery expressions.