Detect an XPath input from an HTTP request

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Metadata

ID: java-security/tainted-xpath

Language: Java

Severity: Warning

Category: Best Practices

Description

This rule identifies potential security vulnerabilities in your code where an XPath expression may be influenced by data coming from an HTTP request. This could lead to what is known as an XPath Injection attack, where an attacker could manipulate the XPath query to access unauthorized data, or potentially cause other harmful effects.

This rule is crucial because XPath Injection is a severe security risk, similar to SQL Injection. If an attacker can control part of an XPath query, they can alter the query’s logic, leading to unauthorized access or exposure to sensitive data.

Never construct XPath queries using string concatenation with unvalidated input. Instead, always use parameterized queries or sanitize the input before using it in an XPath query. If possible, limit the XPath functionality that your application uses to reduce the attack surface. You can also use APIs that automatically protect against XPath Injection, or use a web application firewall to detect and block attack attempts.

Non-Compliant Code Examples

@WebServlet(value = "/xpathi-00/BenchmarkTest01223")
public class BenchmarkTest01223 extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");

        String param = "";
        java.util.Enumeration<String> headers = request.getHeaders("BenchmarkTest01223");

        if (headers != null && headers.hasMoreElements()) {
            param = headers.nextElement(); // just grab first element
        }

        // URL Decode the header value since req.getHeaders() doesn't. Unlike req.getParameters().
        param = java.net.URLDecoder.decode(param, "UTF-8");

        String bar = new Test().doSomething(request, param);

        try {
            java.io.FileInputStream file =
                    new java.io.FileInputStream(
                            org.owasp.benchmark.helpers.Utils.getFileFromClasspath(
                                    "employees.xml", this.getClass().getClassLoader()));
            javax.xml.parsers.DocumentBuilderFactory builderFactory =
                    javax.xml.parsers.DocumentBuilderFactory.newInstance();
            // Prevent XXE
            builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            javax.xml.parsers.DocumentBuilder builder = builderFactory.newDocumentBuilder();
            org.w3c.dom.Document xmlDocument = builder.parse(file);
            javax.xml.xpath.XPathFactory xpf = javax.xml.xpath.XPathFactory.newInstance();
            javax.xml.xpath.XPath xp = xpf.newXPath();

            String expression = "/Employees/Employee[@emplid='" + bar + "']";
            xp.compile(expression).evaluate(xmlDocument, javax.xml.xpath.XPathConstants.NODESET);

            response.getWriter().println("Your query results are: <br/>");

            for (int i = 0; i < nodeList.getLength(); i++) {
                org.w3c.dom.Element value = (org.w3c.dom.Element) nodeList.item(i);
                response.getWriter().println(value.getTextContent() + "<br/>");
            }
        } catch (javax.xml.xpath.XPathExpressionException
                | javax.xml.parsers.ParserConfigurationException
                | org.xml.sax.SAXException e) {
            response.getWriter()
                    .println(
                            "Error parsing XPath input: '"
                                    + org.owasp.esapi.ESAPI.encoder().encodeForHTML(bar)
                                    + "'");
            throw new ServletException(e);
        }
    } // end doPost

    private class Test {

        public String doSomething(HttpServletRequest request, String param)
                throws ServletException, IOException {

            String bar;
            String guess = "ABC";
            char switchTarget = guess.charAt(2);

            // Simple case statement that assigns param to bar on conditions 'A', 'C', or 'D'
            switch (switchTarget) {
                case 'A':
                    bar = param;
                    break;
                case 'B':
                    bar = "bobs_your_uncle";
                    break;
                case 'C':
                case 'D':
                    bar = param;
                    break;
                default:
                    bar = "bobs_your_uncle";
                    break;
            }

            return bar;
        }
    } // end innerclass Test
} // end DataflowThruInnerClass

@WebServlet(value = "/xpathi-00/BenchmarkTest01223")
public class BenchmarkTest01223 extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");

        String param = "";
        java.util.Enumeration<String> headers = request.getHeaders("BenchmarkTest01223");

        if (headers != null && headers.hasMoreElements()) {
            param = headers.nextElement(); // just grab first element
        }

        // URL Decode the header value since req.getHeaders() doesn't. Unlike req.getParameters().
        param = java.net.URLDecoder.decode(param, "UTF-8");

        String bar = new Test().doSomething(request, param);

        try {
            java.io.FileInputStream file =
                    new java.io.FileInputStream(
                            org.owasp.benchmark.helpers.Utils.getFileFromClasspath(
                                    "employees.xml", this.getClass().getClassLoader()));
            javax.xml.parsers.DocumentBuilderFactory builderFactory =
                    javax.xml.parsers.DocumentBuilderFactory.newInstance();
            // Prevent XXE
            builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            javax.xml.parsers.DocumentBuilder builder = builderFactory.newDocumentBuilder();
            org.w3c.dom.Document xmlDocument = builder.parse(file);
            javax.xml.xpath.XPathFactory xpf = javax.xml.xpath.XPathFactory.newInstance();
            javax.xml.xpath.XPath xp = xpf.newXPath();

            String expression = "/Employees/Employee[@emplid='" + bar + "']";
            // ruleid: tainted-xpath-from-http-request
            org.w3c.dom.NodeList nodeList = (org.w3c.dom.NodeList) xp.compile(expression).evaluate(xmlDocument, javax.xml.xpath.XPathConstants.NODESET);

            response.getWriter().println("Your query results are: <br/>");

            for (int i = 0; i < nodeList.getLength(); i++) {
                org.w3c.dom.Element value = (org.w3c.dom.Element) nodeList.item(i);
                response.getWriter().println(value.getTextContent() + "<br/>");
            }
        } catch (javax.xml.xpath.XPathExpressionException
                | javax.xml.parsers.ParserConfigurationException
                | org.xml.sax.SAXException e) {
            response.getWriter()
                    .println(
                            "Error parsing XPath input: '"
                                    + org.owasp.esapi.ESAPI.encoder().encodeForHTML(bar)
                                    + "'");
            throw new ServletException(e);
        }
    } // end doPost

    private class Test {

        public String doSomething(HttpServletRequest request, String param)
                throws ServletException, IOException {

            String bar;
            String guess = "ABC";
            char switchTarget = guess.charAt(2);

            // Simple case statement that assigns param to bar on conditions 'A', 'C', or 'D'
            switch (switchTarget) {
                case 'A':
                    bar = param;
                    break;
                case 'B':
                    bar = "bobs_your_uncle";
                    break;
                case 'C':
                case 'D':
                    bar = param;
                    break;
                default:
                    bar = "bobs_your_uncle";
                    break;
            }

            return bar;
        }
    } // end innerclass Test
} // end DataflowThruInnerClass

Compliant Code Examples

class Class {
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");

        javax.servlet.http.Cookie[] theCookies = request.getCookies();

        String param = "noCookieValueSupplied";
        if (theCookies != null) {
            for (javax.servlet.http.Cookie theCookie : theCookies) {
                if (theCookie.getName().equals("BenchmarkTest00118")) {
                    param = java.net.URLDecoder.decode(theCookie.getValue(), "UTF-8");
                    break;
                }
            }
        }

        String bar;

        // Simple if statement that assigns constant to bar on true condition
        int num = 86;
        if ((7 * 42) - num > 200) bar = "This_should_always_happen";
        else bar = param;

        try {
            java.io.FileInputStream file =
                    new java.io.FileInputStream(
                            org.owasp.benchmark.helpers.Utils.getFileFromClasspath(
                                    "employees.xml", this.getClass().getClassLoader()));
            javax.xml.parsers.DocumentBuilderFactory builderFactory =
                    javax.xml.parsers.DocumentBuilderFactory.newInstance();
            // Prevent XXE
            builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            javax.xml.parsers.DocumentBuilder builder = builderFactory.newDocumentBuilder();
            org.w3c.dom.Document xmlDocument = builder.parse(file);
            javax.xml.xpath.XPathFactory xpf = javax.xml.xpath.XPathFactory.newInstance();
            javax.xml.xpath.XPath xp = xpf.newXPath();

            String expression = "/Employees/Employee[@emplid='" + bar + "']";
            String result = xp.evaluate(expression, xmlDocument);

            response.getWriter().println("Your query results are: " + result + "<br/>");

        } catch (javax.xml.xpath.XPathExpressionException
                | javax.xml.parsers.ParserConfigurationException
                | org.xml.sax.SAXException e) {
            response.getWriter()
                    .println(
                            "Error parsing XPath input: '"
                                    + org.owasp.esapi.ESAPI.encoder().encodeForHTML(bar)
                                    + "'");
            throw new ServletException(e);
        }
    }
}

class Test {

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");

        javax.servlet.http.Cookie[] theCookies = request.getCookies();

        String param = "noCookieValueSupplied";
        if (theCookies != null) {
            for (javax.servlet.http.Cookie theCookie : theCookies) {
                if (theCookie.getName().equals("BenchmarkTest00116")) {
                    param = java.net.URLDecoder.decode(theCookie.getValue(), "UTF-8");
                    break;
                }
            }
        }

        String bar = "safe!";
        java.util.HashMap<String, Object> map51005 = new java.util.HashMap<String, Object>();
        map51005.put("keyA-51005", "a_Value"); // put some stuff in the collection
        map51005.put("keyB-51005", param); // put it in a collection
        map51005.put("keyC", "another_Value"); // put some stuff in the collection
        bar = (String) map51005.get("keyB-51005"); // get it back out
        bar = (String) map51005.get("keyA-51005"); // get safe value back out

        try {
            java.io.FileInputStream file =
                    new java.io.FileInputStream(
                            org.owasp.benchmark.helpers.Utils.getFileFromClasspath(
                                    "employees.xml", this.getClass().getClassLoader()));
            javax.xml.parsers.DocumentBuilderFactory builderFactory =
                    javax.xml.parsers.DocumentBuilderFactory.newInstance();
            // Prevent XXE
            builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            javax.xml.parsers.DocumentBuilder builder = builderFactory.newDocumentBuilder();
            org.w3c.dom.Document xmlDocument = builder.parse(file);
            javax.xml.xpath.XPathFactory xpf = javax.xml.xpath.XPathFactory.newInstance();
            javax.xml.xpath.XPath xp = xpf.newXPath();

            String expression = "/Employees/Employee[@emplid='" + bar + "']";
            org.w3c.dom.NodeList nodeList =
                    (org.w3c.dom.NodeList)
                            xp.compile(expression)
                                    .evaluate(xmlDocument, javax.xml.xpath.XPathConstants.NODESET);

            response.getWriter().println("Your query results are: <br/>");

            for (int i = 0; i < nodeList.getLength(); i++) {
                org.w3c.dom.Element value = (org.w3c.dom.Element) nodeList.item(i);
                response.getWriter().println(value.getTextContent() + "<br/>");
            }
        } catch (javax.xml.xpath.XPathExpressionException
                | javax.xml.parsers.ParserConfigurationException
                | org.xml.sax.SAXException e) {
            response.getWriter()
                    .println(
                            "Error parsing XPath input: '"
                                    + org.owasp.esapi.ESAPI.encoder().encodeForHTML(bar)
                                    + "'");
            throw new ServletException(e);
        }
    }
}


@WebServlet(value = "/xpathi-00/BenchmarkTest00207")
public class BenchmarkTest00207 extends HttpServlet {

    private static final long serialVersionUID = 1L;

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        response.setContentType("text/html;charset=UTF-8");

        String param = "";
        if (request.getHeader("BenchmarkTest00207") != null) {
            param = request.getHeader("BenchmarkTest00207");
        }

        // URL Decode the header value since req.getHeader() doesn't. Unlike req.getParameter().
        param = java.net.URLDecoder.decode(param, "UTF-8");

        String bar = "";
        if (param != null) {
            bar =
                    new String(
                            org.apache.commons.codec.binary.Base64.decodeBase64(
                                    org.apache.commons.codec.binary.Base64.encodeBase64(
                                            param.getBytes())));
        }

        try {
            java.io.FileInputStream file =
                    new java.io.FileInputStream(
                            org.owasp.benchmark.helpers.Utils.getFileFromClasspath(
                                    "employees.xml", this.getClass().getClassLoader()));
            javax.xml.parsers.DocumentBuilderFactory builderFactory =
                    javax.xml.parsers.DocumentBuilderFactory.newInstance();
            // Prevent XXE
            builderFactory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
            javax.xml.parsers.DocumentBuilder builder = builderFactory.newDocumentBuilder();
            org.w3c.dom.Document xmlDocument = builder.parse(file);
            javax.xml.xpath.XPathFactory xpf = javax.xml.xpath.XPathFactory.newInstance();
            javax.xml.xpath.XPath xp = xpf.newXPath();

            String expression = "/Employees/Employee[@emplid='1234']";
            String result = xp.evaluate(expression, xmlDocument);

            response.getWriter().println("Your query results are: " + result + "<br/>");

        } catch (javax.xml.xpath.XPathExpressionException
                | javax.xml.parsers.ParserConfigurationException
                | org.xml.sax.SAXException e) {
            response.getWriter()
                    .println(
                            "Error parsing XPath input: '"
                                    + org.owasp.esapi.ESAPI.encoder().encodeForHTML(bar)
                                    + "'");
            throw new ServletException(e);
        }
    }
}
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