diff --git a/jspwiki-main/src/main/java/org/apache/wiki/plugin/SampleAjaxPlugin.java b/jspwiki-main/src/main/java/org/apache/wiki/plugin/SampleAjaxPlugin.java
index c439cdaa82..f5832eb65b 100644
--- a/jspwiki-main/src/main/java/org/apache/wiki/plugin/SampleAjaxPlugin.java
+++ b/jspwiki-main/src/main/java/org/apache/wiki/plugin/SampleAjaxPlugin.java
@@ -22,6 +22,7 @@ Licensed to the Apache Software Foundation (ASF) under one
 import org.apache.wiki.api.core.Context;
 import org.apache.wiki.api.exceptions.PluginException;
 import org.apache.wiki.api.plugin.Plugin;
+import org.apache.wiki.util.TextUtil;
 
 import jakarta.servlet.ServletException;
 import jakarta.servlet.http.HttpServletRequest;
@@ -46,7 +47,7 @@ public String execute( final Context context, final Map<String, String> params)
 
 		var url = "/" + SERVLET_MAPPING + "/ajaxAction";
 
-		var ajaxParams = params.get("params");
+		var ajaxParams = jsStringEscape( params.get("params") );
 
 		var js = String.format("$('result%s').value='Loading…';"+
 			"var token = Wiki.CsrfProtection;"+
@@ -60,6 +61,31 @@ public String execute( final Context context, final Map<String, String> params)
 		return String.format("<div onclick='%s' style='color: blue; cursor: pointer'>Press Me</div><div id='result%s'></div>", js, id);
 	}
 
+	/**
+	 * Escapes a value for safe embedding inside a single-quoted javascript string that itself
+	 * lives inside a single-quoted HTML event-handler attribute: every character other than an
+	 * ASCII letter or digit is emitted as a javascript unicode escape, so the result can
+	 * terminate neither the enclosing javascript string nor the enclosing attribute.
+	 *
+	 * @param s the raw parameter value, may be {@code null}.
+	 * @return the escaped value, or an empty string if {@code s} was {@code null}.
+	 */
+	static String jsStringEscape( final String s ) {
+		if( s == null ) {
+			return "";
+		}
+		final StringBuilder sb = new StringBuilder( s.length() );
+		for( int i = 0; i < s.length(); i++ ) {
+			final char c = s.charAt( i );
+			if( ( c >= 'a' && c <= 'z' ) || ( c >= 'A' && c <= 'Z' ) || ( c >= '0' && c <= '9' ) ) {
+				sb.append( c );
+			} else {
+				sb.append( String.format( "\\u%04x", ( int )c ) );
+			}
+		}
+		return sb.toString();
+	}
+
 	@Override
 	public String getServletMapping() {
 		return SERVLET_MAPPING;
@@ -72,7 +98,8 @@ public void service( final HttpServletRequest request, final HttpServletResponse
 			Thread.sleep( 5000 ); // Wait 5 seconds
 		} catch( final Exception e ) {
 		}
-		response.getWriter().print( "You called! actionName=" + actionName + " params=" + params );
+		response.getWriter().print( "You called! actionName=" + TextUtil.replaceEntities( actionName )
+				+ " params=" + TextUtil.replaceEntities( String.valueOf( params ) ) );
 	}
 
 }
diff --git a/jspwiki-main/src/test/java/org/apache/wiki/plugin/SampleAjaxPluginTest.java b/jspwiki-main/src/test/java/org/apache/wiki/plugin/SampleAjaxPluginTest.java
new file mode 100644
index 0000000000..cda189891d
--- /dev/null
+++ b/jspwiki-main/src/test/java/org/apache/wiki/plugin/SampleAjaxPluginTest.java
@@ -0,0 +1,44 @@
+/*
+    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.wiki.plugin;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+
+public class SampleAjaxPluginTest {
+
+    @Test
+    public void testParamsCannotBreakOutOfOnclickAttribute() throws Exception {
+        final SampleAjaxPlugin plugin = new SampleAjaxPlugin();
+        final String payload = "\'><img src=x onerror=alert(document.cookie)>";
+        final String result = plugin.execute( null, Map.of( "params", payload ) );
+        Assertions.assertFalse( result.contains( payload ), "raw payload must not reach the HTML output" );
+        Assertions.assertFalse( result.contains( "<img" ), "attribute breakout must not reach the HTML output" );
+    }
+
+    @Test
+    public void testJsStringEscape() {
+        Assertions.assertEquals( "\\u0027\\u003e\\u003cimg", SampleAjaxPlugin.jsStringEscape( "\'><img" ) );
+        Assertions.assertEquals( "abc123", SampleAjaxPlugin.jsStringEscape( "abc123" ) );
+        Assertions.assertEquals( "", SampleAjaxPlugin.jsStringEscape( null ) );
+    }
+
+}