profullstack · CSTRSK · Aug 9, 2026
diff --git a/docs/VULNERABILITY_CATALOG.md b/docs/VULNERABILITY_CATALOG.md
@@ -7,12 +7,12 @@ from each file's header comment, so this page cannot drift from the source.
 
 ## Totals
 
-- **Test cases:** 62
-- **Expected detections:** 62
-- **`VULNERABLE:` markers:** 123 (individual lines a scanner should flag)
-- **`SAFE:` markers:** 73 (lines a scanner must not flag — the false-positive control group)
+- **Test cases:** 63
+- **Expected detections:** 63
+- **`VULNERABLE:` markers:** 124 (individual lines a scanner should flag)
+- **`SAFE:` markers:** 74 (lines a scanner must not flag — the false-positive control group)
 - **Languages:** 8 — dotenv, go, java, javascript, json, python, ruby, text
-- **CWE categories:** 46 — CWE-20, CWE-22, CWE-78, CWE-79, CWE-89, CWE-90, CWE-95, CWE-113, CWE-117, CWE-190, CWE-201, CWE-209, CWE-256, CWE-295, CWE-321, CWE-327, CWE-330, CWE-338, CWE-346, CWE-347, CWE-352, CWE-362, CWE-377, CWE-384, CWE-489, CWE-502, CWE-506, CWE-532, CWE-601, CWE-611, CWE-614, CWE-639, CWE-643, CWE-681, CWE-759, CWE-798, CWE-862, CWE-915, CWE-918, CWE-942, CWE-943, CWE-1236, CWE-1321, CWE-1333, CWE-1336, CWE-1357
+- **CWE categories:** 47 — CWE-20, CWE-22, CWE-78, CWE-79, CWE-89, CWE-90, CWE-91, CWE-95, CWE-113, CWE-117, CWE-190, CWE-201, CWE-209, CWE-256, CWE-295, CWE-321, CWE-327, CWE-330, CWE-338, CWE-346, CWE-347, CWE-352, CWE-362, CWE-377, CWE-384, CWE-489, CWE-502, CWE-506, CWE-532, CWE-601, CWE-611, CWE-614, CWE-639, CWE-643, CWE-681, CWE-759, CWE-798, CWE-862, CWE-915, CWE-918, CWE-942, CWE-943, CWE-1236, CWE-1321, CWE-1333, CWE-1336, CWE-1357
 
 ## How coverage is scored
 
@@ -37,6 +37,7 @@ counts as a detection. See `docs/SCANNER_INTEGRATION.md`.
 |---|---|---|---|---|---|
 | Insecure deserialisation via ObjectInputStream | [`deserialization-object-input-stream.java`](../vulns/java/deserialization-object-input-stream.java) | CWE-502 | critical | yes | 2 vuln / 2 safe |
 | SQL injection via Statement string concatenation | [`sqli-statement-concat.java`](../vulns/java/sqli-statement-concat.java) | CWE-89 | critical | yes | 2 vuln / 1 safe |
+| XPath injection via unvalidated user input in XPath expression | [`cwe-91-java.java`](../vulns/java/cwe-91-java.java) | CWE-91 | high | yes | 1 vuln / 1 safe |
 | Reflected XSS via HttpServletResponse writer | [`xss-response-writer.java`](../vulns/java/xss-response-writer.java) | CWE-79 | high | yes | 2 vuln / 2 safe |
 | XXE via unconfigured DocumentBuilderFactory | [`xxe-document-builder.java`](../vulns/java/xxe-document-builder.java) | CWE-611 | high | yes | 2 vuln / 1 safe |
 

diff --git a/vulns/VULNERABILITY_CATALOG.json b/vulns/VULNERABILITY_CATALOG.json
@@ -2,10 +2,10 @@
   "schema": "threatcrush-testbed-catalog/1",
   "note": "Generated by scripts/generate-catalog.py \u2014 do not edit by hand.",
   "totals": {
-    "test_cases": 62,
-    "expected_detections": 62,
-    "vulnerable_markers": 123,
-    "safe_markers": 73,
+    "test_cases": 63,
+    "expected_detections": 63,
+    "vulnerable_markers": 124,
+    "safe_markers": 74,
     "languages": [
       "dotenv",
       "go",
@@ -32,6 +32,7 @@
       "CWE-79",
       "CWE-89",
       "CWE-90",
+      "CWE-91",
       "CWE-95",
       "CWE-113",
       "CWE-117",
@@ -175,6 +176,29 @@
         56
       ]
     },
+    {
+      "id": "java-xpath-injection-document-builder",
+      "file": "vulns/java/cwe-91-java.java",
+      "title": "XPath injection via unvalidated user input in XPath expression",
+      "category": "java",
+      "language": "java",
+      "cwe": "CWE-91",
+      "cwes": [
+        "CWE-91"
+      ],
+      "severity": "high",
+      "expected_detection": true,
+      "description": "User-controlled input from an HTTP request parameter is",
+      "detection_target": "XPathExpression.evaluate reached from untrusted input",
+      "safe_guard": "Every payload is behind the always-false NEVER_RUN constant and",
+      "attribution": "line",
+      "vulnerable_lines": [
+        51
+      ],
+      "safe_lines": [
+        76
+      ]
+    },
     {
       "id": "java-deserialization-object-input-stream",
       "file": "vulns/java/deserialization-object-input-stream.java",

diff --git a/vulns/java/cwe-91-java.java b/vulns/java/cwe-91-java.java
@@ -0,0 +1,88 @@
+/**
+ * @id java-xpath-injection-document-builder
+ * @test-case XPath injection via unvalidated user input in XPath expression
+ * @cwe CWE-91
+ * @severity high
+ * @language java
+ * @expected-detection true
+ * @description User-controlled input from an HTTP request parameter is
+ *              concatenated directly into an XPath query string used to
+ *              evaluate an XML document. An attacker can inject XPath
+ *              expressions to bypass authentication or extract sensitive
+ *              data from the XML document, leading to information disclosure
+ *              or authorization bypass.
+ * @safe-guard Every payload is behind the always-false NEVER_RUN constant and
+ *             the repository has no Java build file, so nothing is compiled.
+ *             No malicious XPath payload is included in this file.
+ * @detection-target XPathExpression.evaluate reached from untrusted input
+ *                   without parameterized XPath queries or input validation.
+ *
+ * NEVER RUN IN PRODUCTION — intentional test case for scanner validation.
+ */
+package vulns.java;
+
+import javax.xml.parsers.DocumentBuilder;
+import javax.xml.parsers.DocumentBuilderFactory;
+import javax.xml.xpath.XPath;
+import javax.xml.xpath.XPathConstants;
+import javax.xml.xpath.XPathExpression;
+import javax.xml.xpath.XPathFactory;
+import org.w3c.dom.Document;
+import org.xml.sax.InputSource;
+import java.io.StringReader;
+import javax.servlet.http.HttpServletRequest;
+
+public class XPathInjectionDocumentBuilder {
+
+    private static final boolean NEVER_RUN = false;
+
+    public String evaluateUserQueryVulnerable(HttpServletRequest req) throws Exception {
+        if (NEVER_RUN) {
+            String userInput = req.getParameter("username"); // SOURCE
+            String xml = "<users><user><username>admin</username><role>admin</role></user>"
+                       + "<user><username>guest</username><role>guest</role></user></users>";
+
+            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
+            DocumentBuilder builder = factory.newDocumentBuilder();
+            Document doc = builder.parse(new InputSource(new StringReader(xml)));
+
+            XPathFactory xPathFactory = XPathFactory.newInstance();
+            XPath xpath = xPathFactory.newXPath();
+            // VULNERABLE: CWE-91 - user input concatenated into XPath expression
+            String expression = "//user[username='" + userInput + "']/role/text()";
+            XPathExpression expr = xpath.compile(expression);
+            return (String) expr.evaluate(doc, XPathConstants.STRING);
+        }
+        return null;
+    }
+
+    /**
+     * Safe counterpart — the scanner should NOT flag this.
+     *
+     * @expected-detection false
+     */
+    public String evaluateUserQuerySafe(HttpServletRequest req) throws Exception {
+        if (NEVER_RUN) {
+            String userInput = req.getParameter("username");
+            String xml = "<users><user><username>admin</username><role>admin</role></user>"
+                       + "<user><username>guest</username><role>guest</role></user></users>";
+
+            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
+            DocumentBuilder builder = factory.newDocumentBuilder();
+            Document doc = builder.parse(new InputSource(new StringReader(xml)));
+
+            XPathFactory xPathFactory = XPathFactory.newInstance();
+            XPath xpath = xPathFactory.newXPath();
+            // SAFE: parameterized XPath query with variable binding
+            XPathExpression expr = xpath.compile("//user[username=$input]/role/text()");
+            expr.setXPathVariableResolver(variable -> {
+                if ("input".equals(variable.getLocalName())) {
+                    return userInput;
+                }
+                return null;
+            });
+            return (String) expr.evaluate(doc, XPathConstants.STRING);
+        }
+        return null;
+    }
+}