Limit the XML nesting depth for CVE-2022-45688

src/main/java/org/json/XML.java

@@ -232,7 +232,7 @@ public static void noSpace(String string) throws JSONException {
      * @return true if the close tag is processed.
      * @throws JSONException
      */
-    private static boolean parse(XMLTokener x, JSONObject context, String name, XMLParserConfiguration config)
+    private static boolean parse(XMLTokener x, JSONObject context, String name, XMLParserConfiguration config, int currentNestingDepth)
             throws JSONException {
         char c;
         int i;
@@ -402,7 +402,11 @@ private static boolean parse(XMLTokener x, JSONObject context, String name, XMLP
 
                         } else if (token == LT) {
                             // Nested element
-                            if (parse(x, jsonObject, tagName, config)) {
+                            if (currentNestingDepth == config.getMaxNestingDepth()) {
+                                throw x.syntaxError("Maximum nesting depth of " + config.getMaxNestingDepth() + " reached");
+                            }
+
+                            if (parse(x, jsonObject, tagName, config, currentNestingDepth + 1)) {
                                 if (config.getForceList().contains(tagName)) {
                                     // Force the value to be an array
                                     if (jsonObject.length() == 0) {
@@ -644,6 +648,10 @@ public static JSONObject toJSONObject(Reader reader, boolean keepStrings) throws
      * All values are converted as strings, for 1, 01, 29.0 will not be coerced to
      * numbers but will instead be the exact value as seen in the XML document.
      *
+     * This method can parse documents with a maximum nesting depth of 256. If you
+     * need to parse documents with a nesting depth greater than 256, you should use
+     *
+     *
      * @param reader The XML source reader.
      * @param config Configuration options for the parser
      * @return A JSONObject containing the structured data from the XML string.
@@ -655,7 +663,7 @@ public static JSONObject toJSONObject(Reader reader, XMLParserConfiguration conf
         while (x.more()) {
             x.skipPast("<");
             if(x.more()) {
-                parse(x, jo, null, config);
+                parse(x, jo, null, config, 0);
             }
         }
         return jo;

src/main/java/org/json/XMLParserConfiguration.java

@@ -16,6 +16,12 @@
  */
 @SuppressWarnings({""})
 public class XMLParserConfiguration {
+    /**
+     * Used to indicate there's no defined limit to the maximum nesting depth when parsing a XML
+     * document to JSON.
+     */
+    public static final int UNDEFINED_MAXIMUM_NESTING_DEPTH = -1;
+
     /** Original Configuration of the XML Parser. */
     public static final XMLParserConfiguration ORIGINAL
         = new XMLParserConfiguration();
@@ -54,6 +60,12 @@ public class XMLParserConfiguration {
      */
     private Set<String> forceList;
 
+    /**
+     * When parsing the XML into JSON, specifies the tags whose values should be converted
+     * to arrays
+     */
+    private int maxNestingDepth = UNDEFINED_MAXIMUM_NESTING_DEPTH;
+
     /**
      * Default parser configuration. Does not keep strings (tries to implicitly convert
      * values), and the CDATA Tag Name is "content".
@@ -297,4 +309,33 @@ public XMLParserConfiguration withForceList(final Set<String> forceList) {
         newConfig.forceList = Collections.unmodifiableSet(cloneForceList);
         return newConfig;
     }
+
+    /**
+     * The maximum nesting depth that the parser will descend before throwing an exception
+     * when parsing the XML into JSON.
+     * @return the maximum nesting depth set for this configuration
+     */
+    public int getMaxNestingDepth() {
+        return maxNestingDepth;
+    }
+
+    /**
+     * Defines the maximum nesting depth that the parser will descend before throwing an exception
+     * when parsing the XML into JSON. The default max nesting depth is undefined, which means the
+     * parser will go as deep as the maximum call stack size allows. Using any negative value as a
+     * parameter is equivalent to setting no limit to the nesting depth.
+     * @param maxNestingDepth the maximum nesting depth allowed to the XML parser
+     * @return The existing configuration will not be modified. A new configuration is returned.
+     */
+    public XMLParserConfiguration withMaxNestingDepth(int maxNestingDepth) {
+        XMLParserConfiguration newConfig = this.clone();
+
+        if (maxNestingDepth > UNDEFINED_MAXIMUM_NESTING_DEPTH) {
+            newConfig.maxNestingDepth = maxNestingDepth;
+        } else {
+            newConfig.maxNestingDepth = UNDEFINED_MAXIMUM_NESTING_DEPTH;
+        }
+
+        return newConfig;
+    }
 }

src/test/java/org/json/junit/XMLConfigurationTest.java

@@ -1051,6 +1051,29 @@ public void testEmptyTagForceList() {
 
         Util.compareActualVsExpectedJsonObjects(jsonObject, expetedJsonObject);
     }
+
+    @Test
+    public void testMaxNestingDepthIsSet() {
+        XMLParserConfiguration xmlParserConfiguration = XMLParserConfiguration.ORIGINAL;
+
+        assertEquals(xmlParserConfiguration.getMaxNestingDepth(), XMLParserConfiguration.UNDEFINED_MAXIMUM_NESTING_DEPTH);
+
+        xmlParserConfiguration = xmlParserConfiguration.withMaxNestingDepth(42);
+
+        assertEquals(xmlParserConfiguration.getMaxNestingDepth(), 42);
+
+        xmlParserConfiguration = xmlParserConfiguration.withMaxNestingDepth(0);
+
+        assertEquals(xmlParserConfiguration.getMaxNestingDepth(), 0);
+
+        xmlParserConfiguration = xmlParserConfiguration.withMaxNestingDepth(-31415926);
+
+        assertEquals(xmlParserConfiguration.getMaxNestingDepth(), XMLParserConfiguration.UNDEFINED_MAXIMUM_NESTING_DEPTH);
+
+        xmlParserConfiguration = xmlParserConfiguration.withMaxNestingDepth(Integer.MIN_VALUE);
+
+        assertEquals(xmlParserConfiguration.getMaxNestingDepth(), XMLParserConfiguration.UNDEFINED_MAXIMUM_NESTING_DEPTH);
+    }
 
     /**
      * Convenience method, given an input string and expected result,

src/test/java/org/json/junit/XMLTest.java

@@ -1247,6 +1247,65 @@ public void testIndentComplicatedJsonObjectWithArrayAndWithConfig(){
             fail("file writer error: " +e.getMessage());
         }
     }
+
+    @Test
+    public void testMaxNestingDepthOf42IsRespected() {
+        final String wayTooLongMalformedXML = new String(new char[6000]).replace("\0", "<a>");
+
+        final int maxNestingDepth = 42;
+
+        try {
+            XML.toJSONObject(wayTooLongMalformedXML, XMLParserConfiguration.ORIGINAL.withMaxNestingDepth(maxNestingDepth));
+
+            fail("Expecting a JSONException");
+        } catch (JSONException e) {
+            assertTrue("Wrong throwable thrown: not expecting message <" + e.getMessage() + ">",
+                e.getMessage().startsWith("Maximum nesting depth of " + maxNestingDepth));
+        }
+    }
+
+    @Test
+    public void testMaxNestingDepthIsRespectedWithValidXML() {
+        final String perfectlyFineXML = "<Test>\n" +
+            "  <employee>\n" +
+            "    <name>sonoo</name>\n" +
+            "    <salary>56000</salary>\n" +
+            "    <married>true</married>\n" +
+            "  </employee>\n" +
+            "</Test>\n";
+
+        final int maxNestingDepth = 1;
+
+        try {
+            XML.toJSONObject(perfectlyFineXML, XMLParserConfiguration.ORIGINAL.withMaxNestingDepth(maxNestingDepth));
+
+            fail("Expecting a JSONException");
+        } catch (JSONException e) {
+            assertTrue("Wrong throwable thrown: not expecting message <" + e.getMessage() + ">",
+                e.getMessage().startsWith("Maximum nesting depth of " + maxNestingDepth));
+        }
+    }
+
+    @Test
+    public void testMaxNestingDepthWithValidFittingXML() {
+        final String perfectlyFineXML = "<Test>\n" +
+            "  <employee>\n" +
+            "    <name>sonoo</name>\n" +
+            "    <salary>56000</salary>\n" +
+            "    <married>true</married>\n" +
+            "  </employee>\n" +
+            "</Test>\n";
+
+        final int maxNestingDepth = 3;
+
+        try {
+            XML.toJSONObject(perfectlyFineXML, XMLParserConfiguration.ORIGINAL.withMaxNestingDepth(maxNestingDepth));
+        } catch (JSONException e) {
+            e.printStackTrace();
+            fail("XML document should be parsed as its maximum depth fits the maxNestingDepth " +
+                "parameter of the XMLParserConfiguration used");
+        }
+    }
 }