diff --git a/core/src/main/java/com/google/adk/agents/ToolResolver.java b/core/src/main/java/com/google/adk/agents/ToolResolver.java
index 09a3d79c1..2e82961e8 100644
--- a/core/src/main/java/com/google/adk/agents/ToolResolver.java
+++ b/core/src/main/java/com/google/adk/agents/ToolResolver.java
@@ -25,6 +25,7 @@
 import com.google.adk.tools.BaseToolset;
 import com.google.adk.utils.ComponentRegistry;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
@@ -41,6 +42,37 @@ final class ToolResolver {
 
   private static final Logger logger = LoggerFactory.getLogger(LlmAgent.class);
 
+  /**
+   * Allowlist of trusted package prefixes for dynamic class loading from YAML configs.
+   *
+   * <p>Security: Only classes from these packages can be loaded via reflection when specified
+   * in YAML agent configurations. This prevents arbitrary class loading attacks where a
+   * malicious YAML config could specify dangerous classes (e.g., Runtime, ProcessBuilder)
+   * to achieve code execution. This is the Java equivalent of CVE-2026-4810 in adk-python.
+   */
+  private static final ImmutableSet<String> ALLOWED_CLASS_PREFIXES =
+      ImmutableSet.of(
+          "com.google.adk.",
+          "google.adk.");
+
+  /**
+   * Validates that a class name is from an allowed package before dynamic loading.
+   *
+   * @param className the fully qualified class name to validate
+   * @return true if the class is from an allowed package
+   */
+  static boolean isAllowedClassForLoading(String className) {
+    if (isNullOrEmpty(className)) {
+      return false;
+    }
+    for (String prefix : ALLOWED_CLASS_PREFIXES) {
+      if (className.startsWith(prefix)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   private ToolResolver() {}
 
   /**
@@ -270,6 +302,11 @@ static BaseToolset resolveToolsetFromClass(
     if (toolsetClassOpt.isPresent()) {
       toolsetClass = toolsetClassOpt.get();
     } else if (isJavaQualifiedName(className)) {
+      // Security: Only allow class loading from trusted ADK packages
+      if (!isAllowedClassForLoading(className)) {
+        logger.warn("Blocked dynamic class loading from untrusted package: {}", className);
+        return null;
+      }
       // Try reflection to get class
       try {
         Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
@@ -345,6 +382,12 @@ static BaseToolset resolveToolsetInstanceViaReflection(String toolsetName)
     String className = toolsetName.substring(0, lastDotIndex);
     String fieldName = toolsetName.substring(lastDotIndex + 1);
 
+    // Security: Only allow class loading from trusted ADK packages
+    if (!isAllowedClassForLoading(className)) {
+      logger.warn("Blocked dynamic class loading from untrusted package: {}", className);
+      return null;
+    }
+
     Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
 
     try {
@@ -395,6 +438,11 @@ static BaseTool resolveToolFromClass(String className, ToolArgsConfig args, Stri
     if (classOpt.isPresent()) {
       toolClass = classOpt.get();
     } else if (isJavaQualifiedName(className)) {
+      // Security: Only allow class loading from trusted ADK packages
+      if (!isAllowedClassForLoading(className)) {
+        logger.warn("Blocked dynamic class loading from untrusted package: {}", className);
+        return null;
+      }
       // Try reflection to get class
       try {
         Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
@@ -435,7 +483,8 @@ static BaseTool resolveToolFromClass(String className, ToolArgsConfig args, Stri
     // No args provided or empty args, try default constructor
     try {
       Constructor<? extends BaseTool> constructor = toolClass.getDeclaredConstructor();
-      constructor.setAccessible(true);
+      // Security: Do not call setAccessible(true) — only use public constructors
+      // to prevent bypassing access controls on non-public classes.
       return constructor.newInstance();
     } catch (NoSuchMethodException e) {
       throw new ConfigurationException(
@@ -491,6 +540,12 @@ static BaseTool resolveInstanceViaReflection(String toolName)
     String className = toolName.substring(0, lastDotIndex);
     String fieldName = toolName.substring(lastDotIndex + 1);
 
+    // Security: Only allow class loading from trusted ADK packages
+    if (!isAllowedClassForLoading(className)) {
+      logger.warn("Blocked dynamic class loading from untrusted package: {}", className);
+      return null;
+    }
+
     Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
 
     try {
diff --git a/core/src/main/java/com/google/adk/utils/ComponentRegistry.java b/core/src/main/java/com/google/adk/utils/ComponentRegistry.java
index 3b2d0d14a..8d4484fa9 100644
--- a/core/src/main/java/com/google/adk/utils/ComponentRegistry.java
+++ b/core/src/main/java/com/google/adk/utils/ComponentRegistry.java
@@ -437,7 +437,33 @@ private static <T> Optional<Class<? extends T>> getType(String name, Class<T> ty
         .map(clazz -> clazz.asSubclass(type));
   }
 
+  /**
+   * Allowlist of trusted package prefixes for dynamic class loading.
+   *
+   * <p>Security: Only classes from these packages can be loaded via reflection when specified
+   * in YAML agent configurations. This prevents arbitrary class loading attacks (CVE-2026-4810).
+   */
+  private static final Set<String> ALLOWED_CLASS_PREFIXES =
+      Set.of("com.google.adk.", "google.adk.");
+
+  private static boolean isAllowedClassForLoading(String className) {
+    if (isNullOrEmpty(className)) {
+      return false;
+    }
+    for (String prefix : ALLOWED_CLASS_PREFIXES) {
+      if (className.startsWith(prefix)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   private static Optional<Class<? extends BaseToolset>> loadToolsetClass(String className) {
+    // Security: Only allow class loading from trusted ADK packages
+    if (!isAllowedClassForLoading(className)) {
+      logger.warn("Blocked dynamic class loading from untrusted package: {}", className);
+      return Optional.empty();
+    }
     try {
       Class<?> clazz = Thread.currentThread().getContextClassLoader().loadClass(className);
       if (BaseToolset.class.isAssignableFrom(clazz)) {