diff --git a/src/java.base/share/classes/java/lang/ClassLoader.java b/src/java.base/share/classes/java/lang/ClassLoader.java
index 6082bc53297af..511785a5ac8a6 100644
--- a/src/java.base/share/classes/java/lang/ClassLoader.java
+++ b/src/java.base/share/classes/java/lang/ClassLoader.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2013, 2025, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2019, Azul Systems, Inc. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
@@ -52,6 +52,7 @@
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
+import jdk.internal.access.SharedSecrets;
 import jdk.internal.loader.BootLoader;
 import jdk.internal.loader.BuiltinClassLoader;
 import jdk.internal.loader.ClassLoaders;
@@ -1049,14 +1050,22 @@ protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
 
         protectionDomain = preDefineClass(name, protectionDomain);
         String source = defineClassSourceLocation(protectionDomain);
-        Class<?> c = defineClass2(this, name, b, b.position(), len, protectionDomain, source);
-        postDefineClass(c, protectionDomain);
-        return c;
+
+        SharedSecrets.getJavaNioAccess().acquireSession(b);
+        try {
+            Class<?> c = defineClass2(this, name, b, b.position(), len, protectionDomain, source);
+            postDefineClass(c, protectionDomain);
+            return c;
+        } finally {
+            SharedSecrets.getJavaNioAccess().releaseSession(b);
+        }
     }
 
     static native Class<?> defineClass1(ClassLoader loader, String name, byte[] b, int off, int len,
                                         ProtectionDomain pd, String source);
 
+    // Warning: Before calling this method, the provided ByteBuffer must be guarded
+    //          via JavaNioAccess::(acquire|release)Session
     static native Class<?> defineClass2(ClassLoader loader, String name, java.nio.ByteBuffer b,
                                         int off, int len, ProtectionDomain pd,
                                         String source);
diff --git a/test/jdk/java/lang/ClassLoader/defineClass/GuardByteBuffer.java b/test/jdk/java/lang/ClassLoader/defineClass/GuardByteBuffer.java
new file mode 100644
index 0000000000000..785874201c8e5
--- /dev/null
+++ b/test/jdk/java/lang/ClassLoader/defineClass/GuardByteBuffer.java
@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8365203
+ * @summary Tests guarding of ByteBuffers in ClassLoader::defineClass
+ * @run junit GuardByteBuffer
+ */
+
+import org.junit.jupiter.api.Test;
+
+import java.lang.foreign.Arena;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.LockSupport;
+
+final class GuardByteBuffer {
+
+    @Test
+    void guardCrash() throws InterruptedException {
+        final var cl = new ClassLoader() {
+            void tryCrash() {
+                var arena = Arena.ofConfined();
+                int size = 65536;
+                var byteBuffer = arena.allocate(size).asByteBuffer();
+                for (int i = 0; i < size; i += Long.BYTES) {
+                    byteBuffer.putLong(i, ThreadLocalRandom.current().nextLong());
+                }
+                // Close the arena underneath
+                arena.close();
+                defineClass(null, byteBuffer, null);
+            }
+        };
+        final List<Thread> threads = new ArrayList<>();
+        for (int i = 0; i < Runtime.getRuntime().availableProcessors(); i++) {
+            threads.add(Thread.ofPlatform().start(() -> forAWhile(cl::tryCrash)));
+        }
+        for (var thread : threads) {
+            thread.join();
+        }
+    }
+
+    static void forAWhile(Runnable runnable) {
+        final long deadLine = System.nanoTime() + TimeUnit.SECONDS.toNanos(20);
+        while (System.nanoTime() < deadLine) {
+            try {
+                runnable.run();
+            } catch (Throwable _) { }
+        }
+    }
+
+}