diff --git a/openam-core/src/main/java/com/sun/identity/authentication/server/AuthXMLRequest.java b/openam-core/src/main/java/com/sun/identity/authentication/server/AuthXMLRequest.java
index 76b0b9e7ee..5d6908782d 100644
--- a/openam-core/src/main/java/com/sun/identity/authentication/server/AuthXMLRequest.java
+++ b/openam-core/src/main/java/com/sun/identity/authentication/server/AuthXMLRequest.java
@@ -281,7 +281,20 @@ public void setIndexName(String indexName) {
      */
     public void setPrincipal(String className,String principalValue) {
         try {
-            Class clName = Class.forName(className);
+            // className is read from the /authservice (PLL) request XML, so it must not be
+            // resolved with side effects. Load the class without running its static
+            // initializers and verify it is a Principal BEFORE instantiating it: the
+            // (Principal) cast below is evaluated only after newInstance() has already run
+            // the class's static initializer and constructor, so the cast is not a control.
+            // Same hardening as AuthXMLUtils.createCustomCallback
+            // (GHSA-wg5r-wc3x-39vc / CVE-2026-62379).
+            Class clName = Class.forName(className, false,
+                AuthXMLRequest.class.getClassLoader());
+            if (!Principal.class.isAssignableFrom(clName)) {
+                debug.error("AuthXMLRequest.setPrincipal : class " + className
+                    + " is not a java.security.Principal implementation");
+                return;
+            }
             principal = (Principal) clName.newInstance();
         } catch (ClassNotFoundException ce) {
             //debug.error("Error creating class instance " , e); 
diff --git a/openam-core/src/test/java/com/sun/identity/authentication/server/AuthXMLRequestSecurityTest.java b/openam-core/src/test/java/com/sun/identity/authentication/server/AuthXMLRequestSecurityTest.java
new file mode 100644
index 0000000000..91d12c6d13
--- /dev/null
+++ b/openam-core/src/test/java/com/sun/identity/authentication/server/AuthXMLRequestSecurityTest.java
@@ -0,0 +1,103 @@
+/*
+ * The contents of this file are subject to the terms of the Common Development and
+ * Distribution License (the License). You may not use this file except in compliance with the
+ * License.
+ *
+ * You can obtain a copy of the License at legal/CDDLv1.0.txt. See the License for the
+ * specific language governing permission and limitations under the License.
+ *
+ * When distributing Covered Software, include this CDDL Header Notice in each file and include
+ * the License file at legal/CDDLv1.0.txt. If applicable, add the following below the CDDL
+ * Header, with the fields enclosed by brackets [] replaced by your own identifying
+ * information: "Portions copyright [year] [name of copyright owner]".
+ */
+
+package com.sun.identity.authentication.server;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.security.Principal;
+
+import org.testng.annotations.Test;
+
+/**
+ * setPrincipal(String, String) resolves a class by name. It is not reachable in-tree today, but it
+ * is public, so it is held to the same contract as AuthXMLUtils.createCustomCallback after
+ * GHSA-wg5r-wc3x-39vc: a class that is not a Principal must be rejected without being initialized
+ * or instantiated.
+ */
+public class AuthXMLRequestSecurityTest {
+
+    @Test
+    public void setPrincipalRejectsNonPrincipalClassWithoutLoadingOrInstantiatingIt() {
+        ProbeFlags.initialised = false;
+        ProbeFlags.instantiated = false;
+
+        AuthXMLRequest request = new AuthXMLRequest();
+        request.setPrincipal(NonPrincipalProbe.class.getName(), "ignored");
+
+        assertThat(request.getPrincipal())
+                .as("a class that is not a Principal must not become the principal").isNull();
+        assertThat(ProbeFlags.instantiated)
+                .as("the named class must never be instantiated").isFalse();
+        assertThat(ProbeFlags.initialised)
+                .as("the named class must not even be initialized: Class.forName must be called"
+                        + " with initialize=false so an unvalidated name cannot run a static"
+                        + " initializer").isFalse();
+    }
+
+    @Test
+    public void setPrincipalStillAcceptsALegitimatePrincipal() {
+        AuthXMLRequest request = new AuthXMLRequest();
+        request.setPrincipal(LegitimatePrincipal.class.getName(), "ignored");
+
+        assertThat(request.getPrincipal())
+                .as("a genuine Principal implementation must still resolve")
+                .isInstanceOf(LegitimatePrincipal.class);
+    }
+
+    @Test
+    public void setPrincipalIgnoresAnUnknownClassName() {
+        AuthXMLRequest request = new AuthXMLRequest();
+        request.setPrincipal("com.example.NoSuchClassAnywhere", "ignored");
+
+        assertThat(request.getPrincipal()).isNull();
+    }
+
+    /**
+     * The flags live outside the probe on purpose. Reading or writing a static field of a class
+     * triggers that class's initialization, so flags held on the probe itself would be set by the
+     * test's own reset, and the "was it initialized" assertion would pass even against the
+     * unhardened code. Keeping them here means the probe is only ever named by a class literal,
+     * which does not trigger initialization, so the assertion can actually fail.
+     */
+    static final class ProbeFlags {
+
+        static volatile boolean initialised;
+        static volatile boolean instantiated;
+
+        private ProbeFlags() {
+        }
+    }
+
+    /** Not a Principal. Records, elsewhere, whether it was initialized or constructed. */
+    public static class NonPrincipalProbe {
+
+        static {
+            ProbeFlags.initialised = true;
+        }
+
+        public NonPrincipalProbe() {
+            ProbeFlags.instantiated = true;
+        }
+    }
+
+    /** A minimal genuine Principal, to show the guard is not over-broad. */
+    public static class LegitimatePrincipal implements Principal {
+
+        @Override
+        public String getName() {
+            return "legitimate";
+        }
+    }
+}