diff --git a/core/src/main/java/org/apache/struts2/ognl/SecurityMemberAccess.java b/core/src/main/java/org/apache/struts2/ognl/SecurityMemberAccess.java
index 4d552d5948..10fdf65ced 100644
--- a/core/src/main/java/org/apache/struts2/ognl/SecurityMemberAccess.java
+++ b/core/src/main/java/org/apache/struts2/ognl/SecurityMemberAccess.java
@@ -310,6 +310,15 @@ protected boolean checkExclusionList(Object target, Member member) {
     }
 
     /**
+     * Blocks access to classes in the default (unnamed) package.
+     * <p>
+     * The emptiness of {@link #toPackageName(Class)} is the same test as the
+     * {@code getPackage() == null || getPackage().getName().isEmpty()} form this replaced, for every
+     * class shape: {@code getPackage()} is null for arrays, primitives and {@code void}, and names the
+     * unnamed package with the empty string, all of which {@code toPackageName} reports as empty. It
+     * avoids the {@code getPackage()} lookup through the defining classloader's package map, which
+     * ran twice per class here. See WW-5677.
+     *
      * @return {@code true} if member access is allowed
      */
     protected boolean checkDefaultPackageAccess(Object target, Member member) {
@@ -317,7 +326,7 @@ protected boolean checkDefaultPackageAccess(Object target, Member member) {
             return true;
         }
         Class<?> memberClass = member.getDeclaringClass();
-        if (memberClass.getPackage() == null || memberClass.getPackage().getName().isEmpty()) {
+        if (toPackageName(memberClass).isEmpty()) {
             LOG.warn("Class [{}] from the default package is excluded!", memberClass);
             return false;
         }
@@ -325,7 +334,7 @@ protected boolean checkDefaultPackageAccess(Object target, Member member) {
             return true;
         }
         Class<?> targetClass = target.getClass();
-        if (targetClass.getPackage() == null || targetClass.getPackage().getName().isEmpty()) {
+        if (toPackageName(targetClass).isEmpty()) {
             LOG.warn("Class [{}] from the default package is excluded!", targetClass);
             return false;
         }
@@ -407,7 +416,9 @@ public static String toPackageName(Class<?> clazz) {
     }
 
     protected boolean isExcludedPackageNamePatterns(Class<?> clazz) {
-        return excludedPackageNamePatterns.stream().anyMatch(pattern -> pattern.matcher(toPackageName(clazz)).matches());
+        // Resolved once rather than inside the lambda, which re-resolved it per configured pattern.
+        String packageName = toPackageName(clazz);
+        return excludedPackageNamePatterns.stream().anyMatch(pattern -> pattern.matcher(packageName).matches());
     }
 
     protected boolean isExcludedPackageNames(Class<?> clazz) {
diff --git a/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessPackageMatchingTest.java b/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessPackageMatchingTest.java
index 3dfa540dd4..d333b20af6 100644
--- a/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessPackageMatchingTest.java
+++ b/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessPackageMatchingTest.java
@@ -53,6 +53,15 @@ private static boolean legacyPrefixMatch(String packageName, Set<String> matchin
                 .anyMatch(matchingPackages::contains);
     }
 
+    /**
+     * The default-package condition replaced by WW-5677 in {@code checkDefaultPackageAccess},
+     * retained verbatim as the reference oracle. Deliberately calls {@link Class#getPackage()}
+     * directly rather than delegating to production code, so that it cannot drift with it.
+     */
+    private static boolean legacyDefaultPackageCondition(Class<?> clazz) {
+        return clazz.getPackage() == null || clazz.getPackage().getName().isEmpty();
+    }
+
     /**
      * The {@code toPackageName} implementation replaced by WW-5674, retained as the reference oracle.
      */
@@ -168,6 +177,21 @@ public void toPackageNameMatchesLegacyAcrossClassShapes() throws Exception {
         }
     }
 
+    /**
+     * WW-5677 replaced {@code getPackage() == null || getPackage().getName().isEmpty()} in
+     * {@code checkDefaultPackageAccess} with {@code toPackageName(clazz).isEmpty()}. That gate
+     * decides whether a class counts as living in the default package, so the equivalence is
+     * asserted against the frozen oracle over every class shape rather than argued.
+     */
+    @Test
+    public void defaultPackageConditionMatchesLegacyAcrossClassShapes() throws Exception {
+        for (Class<?> clazz : classShapes()) {
+            assertThat(toPackageName(clazz).isEmpty())
+                    .as("default-package condition for %s", clazz.getName())
+                    .isEqualTo(legacyDefaultPackageCondition(clazz));
+        }
+    }
+
     @Test
     public void arraysAndPrimitivesResolveToTheEmptyPackage() {
         assertThat(toPackageName(int.class)).isEmpty();
diff --git a/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessTest.java b/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessTest.java
index 0338636316..4bfb3c2267 100644
--- a/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessTest.java
+++ b/core/src/test/java/org/apache/struts2/ognl/SecurityMemberAccessTest.java
@@ -404,6 +404,33 @@ public void testDefaultPackageExclusionSetting() throws Exception {
         assertFalse("default package isn't excluded!", actual);
     }
 
+    /**
+     * WW-5677 routed {@code checkDefaultPackageAccess} through {@code toPackageName}. A class in a
+     * named package must still pass the gate when the setting is on.
+     */
+    @Test
+    public void testDefaultPackageAccessPermitsNamedPackageClass() throws Exception {
+        sma.useDisallowDefaultPackageAccess(Boolean.TRUE.toString());
+
+        Member member = FooBar.class.getMethod("getStringField");
+
+        assertTrue("a named-package class is blocked!", sma.checkDefaultPackageAccess(new FooBar(), member));
+    }
+
+    /**
+     * WW-5677 equivalence at the shape most likely to break it: an array target reports the empty
+     * package under both the old {@code getPackage() == null} form and the new one, so it must stay
+     * blocked. The member here declares in {@code java.lang}, so only the target branch can block.
+     */
+    @Test
+    public void testDefaultPackageAccessBlocksArrayTarget() throws Exception {
+        sma.useDisallowDefaultPackageAccess(Boolean.TRUE.toString());
+
+        Member member = Object.class.getMethod("toString");
+
+        assertFalse("an array target isn't blocked!", sma.checkDefaultPackageAccess(new String[0], member));
+    }
+
     @Test
     public void testDefaultPackageExclusion2() throws Exception {
         // given