diff --git a/src/core/src/main/kotlin/org/apache/jmeter/save/JMeterStaxDriver.kt b/src/core/src/main/kotlin/org/apache/jmeter/save/JMeterStaxDriver.kt
index fef5c9383a8..74c8d7b4be3 100644
--- a/src/core/src/main/kotlin/org/apache/jmeter/save/JMeterStaxDriver.kt
+++ b/src/core/src/main/kotlin/org/apache/jmeter/save/JMeterStaxDriver.kt
@@ -17,6 +17,8 @@
 
 package org.apache.jmeter.save
 
+import com.ctc.wstx.api.InvalidCharHandler
+import com.ctc.wstx.api.WstxOutputProperties
 import com.thoughtworks.xstream.io.xml.StaxDriver
 import javax.xml.stream.XMLOutputFactory
 
@@ -24,6 +26,18 @@ public class JMeterStaxDriver(
     public val xmlHeader: Boolean = true,
     public val indent: Boolean = true,
 ) : StaxDriver() {
-    override fun createOutputFactory(): XMLOutputFactory =
-        XMLOutputFactoryDelegate(super.createOutputFactory(), xmlHeader = xmlHeader, indent = indent)
+    override fun createOutputFactory(): XMLOutputFactory {
+        val factory = super.createOutputFactory()
+        // Woodstox rejects XML 1.0-illegal characters (NUL, C0 controls) by default.
+        // Replace them so JTL/JMX save of binary payloads does not fail (#6761).
+        factory.setProperty(
+            WstxOutputProperties.P_OUTPUT_INVALID_CHAR_HANDLER,
+            InvalidCharHandler.ReplacingHandler(INVALID_XML_CHAR_REPLACEMENT)
+        )
+        return XMLOutputFactoryDelegate(factory, xmlHeader = xmlHeader, indent = indent)
+    }
+
+    private companion object {
+        const val INVALID_XML_CHAR_REPLACEMENT = ' '
+    }
 }
diff --git a/src/core/src/test/java/org/apache/jmeter/save/SaveServiceInvalidXmlCharTest.java b/src/core/src/test/java/org/apache/jmeter/save/SaveServiceInvalidXmlCharTest.java
new file mode 100644
index 00000000000..58e64ed83ef
--- /dev/null
+++ b/src/core/src/test/java/org/apache/jmeter/save/SaveServiceInvalidXmlCharTest.java
@@ -0,0 +1,72 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.jmeter.save;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import java.io.ByteArrayOutputStream;
+import java.io.StringWriter;
+import java.nio.charset.StandardCharsets;
+
+import org.apache.jmeter.junit.JMeterTestCase;
+import org.apache.jmeter.samplers.SampleEvent;
+import org.apache.jmeter.samplers.SampleResult;
+import org.apache.jmeter.samplers.SampleSaveConfiguration;
+import org.apache.jmeter.testelement.property.StringProperty;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Regression for <a href="https://github.com/apache/jmeter/issues/6761">#6761</a>:
+ * Woodstox rejects characters that are illegal in XML 1.0 when saving JTL/JMX.
+ */
+public class SaveServiceInvalidXmlCharTest extends JMeterTestCase {
+
+    private static final String ILLEGAL_XML_CHARS = "pre\u0000mid\u001fsuf";
+
+    @Test
+    void saveSampleResultAllowsIllegalXmlCharsInSamplerData() {
+        SampleSaveConfiguration saveConfig = new SampleSaveConfiguration();
+        saveConfig.setSamplerData(true);
+
+        SampleResult result = new SampleResult();
+        result.setSaveConfig(saveConfig);
+        result.setSampleLabel("binary-body");
+        result.setSamplerData(ILLEGAL_XML_CHARS);
+
+        StringWriter writer = new StringWriter();
+        assertDoesNotThrow(() -> SaveService.saveSampleResult(new SampleEvent(result, "tg"), writer));
+
+        String xml = writer.toString();
+        assertFalse(xml.isEmpty(), "JTL output should not be empty");
+        assertFalse(xml.indexOf('\u0000') >= 0, "NUL must not appear in well-formed XML");
+        assertFalse(xml.indexOf('\u001f') >= 0, "C1 control 0x1F must not appear in XML 1.0");
+    }
+
+    @Test
+    void saveElementAllowsNulInStringProperty() {
+        StringProperty property = new StringProperty("bin", ILLEGAL_XML_CHARS);
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+        assertDoesNotThrow(() -> SaveService.saveElement(property, out));
+
+        String xml = out.toString(StandardCharsets.UTF_8);
+        assertFalse(xml.isEmpty(), "JMX fragment should not be empty");
+        assertFalse(xml.indexOf('\u0000') >= 0, "NUL must not appear in well-formed XML");
+        assertFalse(xml.indexOf('\u001f') >= 0, "C1 control 0x1F must not appear in XML 1.0");
+    }
+}
diff --git a/xdocs/changes.xml b/xdocs/changes.xml
index 56b5657563c..7b9fe512b71 100644
--- a/xdocs/changes.xml
+++ b/xdocs/changes.xml
@@ -126,6 +126,7 @@ Summary
     <li><issue>5937</issue>Remove deprecated Log4j package scanning and configure plugin metadata processing to improve startup time and avoid deprecation warnings. Contributed by Piotr P. Karwasz (github.com/piotrgithub)</li>
     <li><pr>6620</pr>Fix report generation paths so dashboard output files are created in the correct location after internal refactoring.</li>
     <li><bug>6456</bug>Handle malformed percent-encoded URLs gracefully when recording HTTP traffic, logging a warning instead of failing the recording.</li>
+    <li><issue>6761</issue>Allow XML save of sample results and test plans that contain characters illegal in XML 1.0 (NUL and C0 controls) after the Woodstox migration.</li>
   </ul>
  <!--  =================== Thanks =================== -->