diff --git a/bom/build.gradle.kts b/bom/build.gradle.kts
index 5febf6f0b335..6d19bc352a1e 100644
--- a/bom/build.gradle.kts
+++ b/bom/build.gradle.kts
@@ -107,6 +107,7 @@ dependencies {
         apiv("org.apache.commons:commons-dbcp2")
         apiv("org.apache.commons:commons-math3")
         apiv("org.apache.commons:commons-pool2")
+        apiv("org.apache.commons:commons-secure-xml")
         apiv("org.apache.commons:commons-collections4")
         apiv("org.apache.commons:commons-text")
         apiv("org.apache.geode:geode-core")
diff --git a/core/build.gradle.kts b/core/build.gradle.kts
index 086f114480e4..1a88bcd0df09 100644
--- a/core/build.gradle.kts
+++ b/core/build.gradle.kts
@@ -70,6 +70,7 @@ dependencies {
     implementation("net.hydromatic:aggdesigner-algorithm")
     implementation("org.apache.commons:commons-dbcp2")
     implementation("org.apache.commons:commons-math3")
+    implementation("org.apache.commons:commons-secure-xml")
     implementation("org.apache.commons:commons-text")
     implementation("org.jooq:joou-java-6")
     implementation("commons-io:commons-io")
diff --git a/core/src/main/java/org/apache/calcite/runtime/SpatialTypeUtils.java b/core/src/main/java/org/apache/calcite/runtime/SpatialTypeUtils.java
index f23514370e5a..ce3530106557 100644
--- a/core/src/main/java/org/apache/calcite/runtime/SpatialTypeUtils.java
+++ b/core/src/main/java/org/apache/calcite/runtime/SpatialTypeUtils.java
@@ -21,6 +21,8 @@
 import org.apache.calcite.linq4j.function.Experimental;
 import org.apache.calcite.linq4j.function.Strict;
 
+import org.apache.commons.xml.secure.SecureSAXParserFactory;
+
 import org.locationtech.jts.geom.Coordinate;
 import org.locationtech.jts.geom.Geometry;
 import org.locationtech.jts.geom.GeometryFactory;
@@ -31,14 +33,17 @@
 import org.locationtech.jts.io.WKTWriter;
 import org.locationtech.jts.io.geojson.GeoJsonReader;
 import org.locationtech.jts.io.geojson.GeoJsonWriter;
-import org.locationtech.jts.io.gml2.GMLReader;
+import org.locationtech.jts.io.gml2.GMLHandler;
 import org.locationtech.jts.io.gml2.GMLWriter;
+import org.xml.sax.InputSource;
 import org.xml.sax.SAXException;
 
 import java.io.IOException;
+import java.io.StringReader;
 import java.util.Locale;
 import java.util.regex.Pattern;
 import javax.xml.parsers.ParserConfigurationException;
+import javax.xml.parsers.SAXParser;
 
 import static java.lang.Integer.parseInt;
 
@@ -130,16 +135,31 @@ public static Geometry fromGeoJson(String geoJson) {
   /**
    * Constructs a geometry from a GML representation.
    *
+   * <p>The GML is parsed by a SAX parser from Apache Commons Secure XML, which
+   * does not fetch external DTDs or entities.
+   *
    * @param gml a GML
    * @return a geometry
    */
   public static Geometry fromGml(String gml) {
+    final SAXParser parser;
+    try {
+      // Not namespace-aware, like JTS's GMLReader:
+      // GML values may use an undeclared "gml:" prefix
+      parser = SecureSAXParserFactory.newInstance().newSAXParser();
+    } catch (ParserConfigurationException | SAXException e) {
+      // Tested parsers reject unsupported features eagerly in the factory, not in
+      // newSAXParser, so an exception here indicates a classpath problem
+      throw new IllegalStateException(e);
+    }
+    @SuppressWarnings("argument.type.incompatible") // delegate is documented as nullable
+    final GMLHandler handler = new GMLHandler(GEOMETRY_FACTORY, null);
     try {
-      GMLReader reader = new GMLReader();
-      return reader.read(gml, GEOMETRY_FACTORY);
-    } catch (SAXException | IOException | ParserConfigurationException e) {
+      parser.parse(new InputSource(new StringReader(gml)), handler);
+    } catch (SAXException | IOException e) {
       throw new RuntimeException("Unable to parse GML");
     }
+    return handler.getGeometry();
   }
 
   /**
diff --git a/gradle.properties b/gradle.properties
index 2f9bed80d22f..9559520f9268 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -95,6 +95,7 @@ commons-dbcp2.version=2.11.0
 commons-io.version=2.15.0
 commons-math3.version=3.6.1
 commons-pool2.version=2.12.0
+commons-secure-xml.version=1.0.0
 commons-collections4.version=4.4
 commons-text.version=1.11.0
 dropwizard-metrics.version=4.0.5
diff --git a/src/main/config/forbidden-apis/signatures.txt b/src/main/config/forbidden-apis/signatures.txt
index c7c95aa1f776..be50a277420e 100644
--- a/src/main/config/forbidden-apis/signatures.txt
+++ b/src/main/config/forbidden-apis/signatures.txt
@@ -121,3 +121,12 @@ java.net.URL#<init>(java.net.URL, java.lang.String, java.net.URLStreamHandler)
 java.net.URL#<init>(java.lang.String, java.lang.String, int, java.lang.String)
 java.net.URL#<init>(java.lang.String, java.lang.String, java.lang.String)
 java.net.URL#<init>(java.lang.String, java.lang.String, int, java.lang.String, java.net.URLStreamHandler)
+
+# Only Java 8 methods: Gradle may run on Java 8, where signatures of
+# newer methods fail to parse, and code compiled for Java 8 cannot call them
+@defaultMessage Use org.apache.commons.xml.secure.SecureSAXParserFactory instead
+javax.xml.parsers.SAXParserFactory#newInstance(**)
+org.xml.sax.helpers.XMLReaderFactory#createXMLReader(**)
+
+@defaultMessage GMLReader creates an unsecured SAX parser; parse with GMLHandler and SecureSAXParserFactory instead
+org.locationtech.jts.io.gml2.GMLReader