Constructing a dynamic XPath query with user input could allow an attacker to modify the statement's meaning.
XPath injection occurs when:
1. Data enters a program from an untrusted source.
2. The data used to dynamically construct an XPath query.
Example 1: The following code dynamically constructs and executes an XPath query that retrieves an e-mail address for a given account ID. The account ID is read from an HTTP request, and is therefore untrusted.
...
String acctID = request.getParameter("acctID");
String query = null;
if(acctID != null) {
StringBuffer sb = new StringBuffer("/accounts/account[acctID='");
sb.append(acctID);
sb.append("']/email/text()");
query = sb.toString();
}
DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
domFactory.setNamespaceAware(true);
DocumentBuilder builder = domFactory.newDocumentBuilder();
Document doc = builder.parse("accounts.xml");
XPathFactory factory = XPathFactory.newInstance();
XPath xpath = factory.newXPath();
XPathExpression expr = xpath.compile(query);
Object result = expr.evaluate(doc, XPathConstants.NODESET);
...
/accounts/account[acctID='1']/email/text()
acctID
does not contain a single-quote character. If an attacker enters the string 1' or '1' = '1
for acctID
, then the query becomes the following:/accounts/account[acctID='1' or '1' = '1']/email/text()
1' or '1' = '1
condition causes the where clause to always evaluate to true, so the query becomes logically equivalent to the much simpler query://email/text()
[1] Standards Mapping - OWASP Top 10 2010 - (OWASP 2010) A1 Injection
[2] Standards Mapping - OWASP Top 10 2007 - (OWASP 2007) A2 Injection Flaws
[3] Standards Mapping - OWASP Top 10 2004 - (OWASP 2004) A6 Injection Flaws
[4] Standards Mapping - Security Technical Implementation Guide Version 3 - (STIG 3) APP3510 CAT I
[5] Standards Mapping - Common Weakness Enumeration - (CWE) CWE ID 643
[6] Standards Mapping - Payment Card Industry Data Security Standard Version 1.2 - (PCI 1.2) Requirement 6.3.1.1, Requirement 6.5.2
[7] Standards Mapping - Payment Card Industry Data Security Standard Version 2.0 - (PCI 2.0) Requirement 6.5.1
[8] Standards Mapping - Payment Card Industry Data Security Standard Version 1.1 - (PCI 1.1) Requirement 6.5.6
[9] Standards Mapping - FIPS200 - (FISMA) SI
[10] Standards Mapping - Web Application Security Consortium 24 + 2 - (WASC 24 + 2) XPath Injection