diff --git a/Stack/Opc.Ua.Core/Stack/Configuration/ConfiguredEndpoints.cs b/Stack/Opc.Ua.Core/Stack/Configuration/ConfiguredEndpoints.cs
index 240b143ed..23ffebf91 100644
--- a/Stack/Opc.Ua.Core/Stack/Configuration/ConfiguredEndpoints.cs
+++ b/Stack/Opc.Ua.Core/Stack/Configuration/ConfiguredEndpoints.cs
@@ -1427,7 +1427,37 @@ private static EndpointDescriptionCollection MatchEndpoints(
             // no matches (security parameters may have changed).
             if (matches.Count == 0)
             {
-                matches = collection;
+                // if specific security parameters were requested, throw appropriate error
+                bool hasSpecificPolicy = !string.IsNullOrEmpty(securityPolicyUri);
+                bool hasSpecificMode = securityMode != MessageSecurityMode.Invalid;
+
+                if (hasSpecificPolicy && hasSpecificMode)
+                {
+                    throw ServiceResultException.Create(
+                        StatusCodes.BadSecurityPolicyRejected,
+                        "Server does not support the requested security policy '{0}' and security mode '{1}'.",
+                        securityPolicyUri,
+                        securityMode);
+                }
+                else if (hasSpecificPolicy)
+                {
+                    throw ServiceResultException.Create(
+                        StatusCodes.BadSecurityPolicyRejected,
+                        "Server does not support the requested security policy '{0}'.",
+                        securityPolicyUri);
+                }
+                else if (hasSpecificMode)
+                {
+                    throw ServiceResultException.Create(
+                        StatusCodes.BadSecurityModeRejected,
+                        "Server does not support the requested security mode '{0}'.",
+                        securityMode);
+                }
+                else
+                {
+                    // no specific security parameters were requested, fall back to any endpoint
+                    matches = collection;
+                }
             }
 
             // check if list has to be narrowed down further.
diff --git a/Tests/Opc.Ua.Core.Tests/Stack/Client/ConfiguredEndpointTests.cs b/Tests/Opc.Ua.Core.Tests/Stack/Client/ConfiguredEndpointTests.cs
new file mode 100644
index 000000000..4c7bda9f0
--- /dev/null
+++ b/Tests/Opc.Ua.Core.Tests/Stack/Client/ConfiguredEndpointTests.cs
@@ -0,0 +1,271 @@
+/* ========================================================================
+ * Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
+ *
+ * OPC Foundation MIT License 1.00
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following
+ * conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ * The complete license agreement can be found here:
+ * http://opcfoundation.org/License/MIT/1.00/
+ * ======================================================================*/
+
+using System;
+using System.Reflection;
+using NUnit.Framework;
+using Opc.Ua.Tests;
+using Assert = NUnit.Framework.Legacy.ClassicAssert;
+
+namespace Opc.Ua.Core.Tests.Stack.Client
+{
+    /// <summary>
+    /// Tests for ConfiguredEndpoint matching.
+    /// </summary>
+    [TestFixture]
+    [Category("Client")]
+    [SetCulture("en-us")]
+    [SetUICulture("en-us")]
+    [Parallelizable]
+    public class ConfiguredEndpointTests
+    {
+        /// <summary>
+        /// Test that when a requested security policy is not supported by the server,
+        /// BadSecurityPolicyRejected is thrown instead of BadUserAccessDenied.
+        /// </summary>
+        [Test]
+        public void MatchEndpoints_ThrowsBadSecurityPolicyRejected_WhenPolicyNotSupported()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+
+            // Create server endpoints with only None and Basic256Sha256
+            var serverEndpoints = new EndpointDescriptionCollection
+            {
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.None,
+                    SecurityPolicyUri = SecurityPolicies.None
+                },
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.SignAndEncrypt,
+                    SecurityPolicyUri = SecurityPolicies.Basic256Sha256
+                }
+            };
+
+            // Try to match with a security policy that doesn't exist (Aes256_Sha256_RsaPss)
+            var ex = Assert.Throws<TargetInvocationException>(() =>
+            {
+                InvokeMatchEndpoints(
+                    serverEndpoints,
+                    new Uri("opc.tcp://localhost:4840"),
+                    MessageSecurityMode.SignAndEncrypt,
+                    SecurityPolicies.Aes256_Sha256_RsaPss
+                );
+            });
+
+            Assert.IsInstanceOf<ServiceResultException>(ex.InnerException);
+            var serviceException = (ServiceResultException)ex.InnerException;
+            Assert.AreEqual(StatusCodes.BadSecurityPolicyRejected, serviceException.StatusCode);
+            Assert.That(serviceException.Message, Does.Contain(SecurityPolicies.Aes256_Sha256_RsaPss));
+        }
+
+        /// <summary>
+        /// Test that when a requested security mode is not supported by the server,
+        /// BadSecurityModeRejected is thrown.
+        /// </summary>
+        [Test]
+        public void MatchEndpoints_ThrowsBadSecurityModeRejected_WhenModeNotSupported()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+
+            // Create server endpoints with only None security mode
+            var serverEndpoints = new EndpointDescriptionCollection
+            {
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.None,
+                    SecurityPolicyUri = SecurityPolicies.None
+                }
+            };
+
+            // Try to match with SignAndEncrypt mode that doesn't exist
+            var ex = Assert.Throws<TargetInvocationException>(() =>
+            {
+                InvokeMatchEndpoints(
+                    serverEndpoints,
+                    new Uri("opc.tcp://localhost:4840"),
+                    MessageSecurityMode.SignAndEncrypt,
+                    null // no specific policy requested, only mode
+                );
+            });
+
+            Assert.IsInstanceOf<ServiceResultException>(ex.InnerException);
+            var serviceException = (ServiceResultException)ex.InnerException;
+            Assert.AreEqual(StatusCodes.BadSecurityModeRejected, serviceException.StatusCode);
+            Assert.That(serviceException.Message, Does.Contain("SignAndEncrypt"));
+        }
+
+        /// <summary>
+        /// Test that when both security policy and mode are not supported,
+        /// BadSecurityPolicyRejected is thrown with information about both.
+        /// </summary>
+        [Test]
+        public void MatchEndpoints_ThrowsBadSecurityPolicyRejected_WhenBothPolicyAndModeNotSupported()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+
+            // Create server endpoints with only None
+            var serverEndpoints = new EndpointDescriptionCollection
+            {
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.None,
+                    SecurityPolicyUri = SecurityPolicies.None
+                }
+            };
+
+            // Try to match with both policy and mode that don't exist
+            var ex = Assert.Throws<TargetInvocationException>(() =>
+            {
+                InvokeMatchEndpoints(
+                    serverEndpoints,
+                    new Uri("opc.tcp://localhost:4840"),
+                    MessageSecurityMode.SignAndEncrypt,
+                    SecurityPolicies.Basic256Sha256
+                );
+            });
+
+            Assert.IsInstanceOf<ServiceResultException>(ex.InnerException);
+            var serviceException = (ServiceResultException)ex.InnerException;
+            Assert.AreEqual(StatusCodes.BadSecurityPolicyRejected, serviceException.StatusCode);
+            Assert.That(serviceException.Message, Does.Contain(SecurityPolicies.Basic256Sha256));
+            Assert.That(serviceException.Message, Does.Contain("SignAndEncrypt"));
+        }
+
+        /// <summary>
+        /// Test that when no specific security parameters are requested,
+        /// the method returns available endpoints without throwing.
+        /// </summary>
+        [Test]
+        public void MatchEndpoints_ReturnsEndpoints_WhenNoSecurityParametersSpecified()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+
+            // Create server endpoints
+            var serverEndpoints = new EndpointDescriptionCollection
+            {
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.None,
+                    SecurityPolicyUri = SecurityPolicies.None
+                },
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.SignAndEncrypt,
+                    SecurityPolicyUri = SecurityPolicies.Basic256Sha256
+                }
+            };
+
+            // Match without specifying security parameters
+            var matches = InvokeMatchEndpoints(
+                serverEndpoints,
+                new Uri("opc.tcp://localhost:4840"),
+                MessageSecurityMode.Invalid,
+                null
+            );
+
+            // Should return available endpoints
+            Assert.IsNotNull(matches);
+            Assert.Greater(matches.Count, 0);
+        }
+
+        /// <summary>
+        /// Test that matching works correctly when the requested security parameters exist.
+        /// </summary>
+        [Test]
+        public void MatchEndpoints_ReturnsMatchingEndpoint_WhenSecurityParametersMatch()
+        {
+            ITelemetryContext telemetry = NUnitTelemetryContext.Create();
+
+            // Create server endpoints
+            var serverEndpoints = new EndpointDescriptionCollection
+            {
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.None,
+                    SecurityPolicyUri = SecurityPolicies.None
+                },
+                new EndpointDescription
+                {
+                    EndpointUrl = "opc.tcp://localhost:4840",
+                    SecurityMode = MessageSecurityMode.SignAndEncrypt,
+                    SecurityPolicyUri = SecurityPolicies.Basic256Sha256
+                }
+            };
+
+            // Match with existing security parameters
+            var matches = InvokeMatchEndpoints(
+                serverEndpoints,
+                new Uri("opc.tcp://localhost:4840"),
+                MessageSecurityMode.SignAndEncrypt,
+                SecurityPolicies.Basic256Sha256
+            );
+
+            // Should return the matching endpoint
+            Assert.IsNotNull(matches);
+            Assert.AreEqual(1, matches.Count);
+            Assert.AreEqual(SecurityPolicies.Basic256Sha256, matches[0].SecurityPolicyUri);
+            Assert.AreEqual(MessageSecurityMode.SignAndEncrypt, matches[0].SecurityMode);
+        }
+
+        /// <summary>
+        /// Helper method to invoke the private MatchEndpoints method via reflection.
+        /// </summary>
+        private EndpointDescriptionCollection InvokeMatchEndpoints(
+            EndpointDescriptionCollection collection,
+            Uri endpointUrl,
+            MessageSecurityMode securityMode,
+            string securityPolicyUri)
+        {
+            var configuredEndpointType = typeof(ConfiguredEndpoint);
+            var matchEndpointsMethod = configuredEndpointType.GetMethod(
+                "MatchEndpoints",
+                BindingFlags.NonPublic | BindingFlags.Static,
+                null,
+                new[] { typeof(EndpointDescriptionCollection), typeof(Uri), typeof(MessageSecurityMode), typeof(string) },
+                null
+            );
+
+            Assert.IsNotNull(matchEndpointsMethod, "MatchEndpoints method not found");
+
+            return (EndpointDescriptionCollection)matchEndpointsMethod.Invoke(
+                null,
+                new object[] { collection, endpointUrl, securityMode, securityPolicyUri }
+            );
+        }
+    }
+}