diff --git a/sdm/src/main/java/com/sap/cds/sdm/constants/SDMErrorMessages.java b/sdm/src/main/java/com/sap/cds/sdm/constants/SDMErrorMessages.java
index 14cae539f..8ff266c24 100644
--- a/sdm/src/main/java/com/sap/cds/sdm/constants/SDMErrorMessages.java
+++ b/sdm/src/main/java/com/sap/cds/sdm/constants/SDMErrorMessages.java
@@ -143,6 +143,12 @@ private SDMErrorMessages() {
   public static final String INVALID_SECONDARY_PROPERTIES_FOR_MOVE_SUFFIX =
       ". Attachment rolled back to source.";
   public static final String SDM_MOVE_OPERATION_FAILED = "SDM move operation failed";
+  public static final String FAILED_TO_COPY_ATTACHMENTS_PREFIX =
+      "Failed to copy the following attachments:\n";
+  public static final String INVALID_SECONDARY_PROPERTIES_FOR_COPY_PREFIX =
+      "Invalid secondary properties detected: ";
+  public static final String INVALID_SECONDARY_PROPERTIES_FOR_COPY_SUFFIX =
+      ". Attachment not copied.";
   public static final String FAILED_TO_ACCESS_ERROR_KEY_FIELDS =
       "Failed to access SDM error key fields";
   public static final String FAILED_TO_ACCESS_ERROR_MESSAGES_FIELDS =
diff --git a/sdm/src/main/java/com/sap/cds/sdm/constants/SDMUIErrorKeys.java b/sdm/src/main/java/com/sap/cds/sdm/constants/SDMUIErrorKeys.java
index 8eead9791..c98e89c7e 100644
--- a/sdm/src/main/java/com/sap/cds/sdm/constants/SDMUIErrorKeys.java
+++ b/sdm/src/main/java/com/sap/cds/sdm/constants/SDMUIErrorKeys.java
@@ -87,6 +87,12 @@ private SDMUIErrorKeys() {}
       "SDM.invalidSecondaryPropertiesForMovePrefix";
   public static final String INVALID_SECONDARY_PROPERTIES_FOR_MOVE_SUFFIX_KEY =
       "SDM.invalidSecondaryPropertiesForMoveSuffix";
+  public static final String FAILED_TO_COPY_ATTACHMENTS_PREFIX_KEY =
+      "SDM.failedToCopyAttachmentsPrefix";
+  public static final String INVALID_SECONDARY_PROPERTIES_FOR_COPY_PREFIX_KEY =
+      "SDM.invalidSecondaryPropertiesForCopyPrefix";
+  public static final String INVALID_SECONDARY_PROPERTIES_FOR_COPY_SUFFIX_KEY =
+      "SDM.invalidSecondaryPropertiesForCopySuffix";
   public static final String MAX_COUNT_ERROR_MESSAGE_KEY = "SDM.maxCountErrorMessage";
 
   public static Map<String, Object> getAllUIErrorKeys() {
diff --git a/sdm/src/main/java/com/sap/cds/sdm/service/handler/SDMCustomServiceHandler.java b/sdm/src/main/java/com/sap/cds/sdm/service/handler/SDMCustomServiceHandler.java
index b393a30a9..d7789e67c 100644
--- a/sdm/src/main/java/com/sap/cds/sdm/service/handler/SDMCustomServiceHandler.java
+++ b/sdm/src/main/java/com/sap/cds/sdm/service/handler/SDMCustomServiceHandler.java
@@ -127,14 +127,42 @@ public void copyAttachments(AttachmentCopyEventContext context) throws IOExcepti
     Boolean isSystemUser = context.getSystemUser();
 
     SDMCredentials sdmCredentials = tokenHandler.getSDMCredentials();
+
+    List<String> objectIds = context.getObjectIds();
+
+    if (!customPropertiesInSDM.isEmpty()) {
+      List<Map<String, String>> copyFailures =
+          findAttachmentsWithInvalidSecondaryProperties(
+              objectIds, customPropertiesInSDM, repositoryId, sdmCredentials, isSystemUser);
+      if (!copyFailures.isEmpty()) {
+        buildAndWarnCopyFailures(copyFailures, context);
+        // Remove invalid objectIds and proceed with valid ones
+        Set<String> invalidObjectIds =
+            copyFailures.stream()
+                .map(failure -> failure.get(OBJECT_ID_KEY))
+                .collect(Collectors.toSet());
+        objectIds =
+            objectIds.stream()
+                .filter(id -> !invalidObjectIds.contains(id))
+                .collect(Collectors.toList());
+        if (objectIds.isEmpty()) {
+          context.setCompleted();
+          logger.debug("END: Copy attachments event - all attachments have invalid properties");
+          return;
+        }
+        logger.info(
+            "Proceeding with {} valid attachments after filtering out {} invalid ones",
+            objectIds.size(),
+            invalidObjectIds.size());
+      }
+    }
+
     // Check if folder exists before trying to create it
     boolean folderExists =
         sdmService.getFolderIdByPath(folderName, repositoryId, sdmCredentials, isSystemUser)
             != null;
     String folderId = ensureFolderExists(folderName, repositoryId, sdmCredentials, isSystemUser);
 
-    List<String> objectIds = context.getObjectIds();
-
     CopyAttachmentsRequest request =
         CopyAttachmentsRequest.builder()
             .context(context)
@@ -178,6 +206,97 @@ public void copyAttachments(AttachmentCopyEventContext context) throws IOExcepti
     logger.debug("END: Copy attachments event");
   }
 
+  /**
+   * Checks source attachments for invalid secondary properties before copy. Returns a list of
+   * failures if any attachment has invalid properties; returns empty list if all are valid
+   */
+  private List<Map<String, String>> findAttachmentsWithInvalidSecondaryProperties(
+      List<String> objectIds,
+      Set<String> customPropertiesInSDM,
+      String repositoryId,
+      SDMCredentials sdmCredentials,
+      Boolean isSystemUser)
+      throws IOException {
+    List<String> secondaryTypes =
+        sdmService.getSecondaryTypes(repositoryId, sdmCredentials, isSystemUser);
+    List<String> validSecondaryProperties =
+        sdmService.getValidSecondaryProperties(
+            secondaryTypes, sdmCredentials, repositoryId, isSystemUser);
+
+    List<Map<String, String>> failures = new ArrayList<>();
+    for (String objectId : objectIds) {
+      List<String> invalidProperties =
+          getInvalidPropertiesForObject(
+              objectId,
+              customPropertiesInSDM,
+              validSecondaryProperties,
+              sdmCredentials,
+              isSystemUser);
+      if (!invalidProperties.isEmpty()) {
+        Map<String, String> failure = new HashMap<>();
+        failure.put(OBJECT_ID_KEY, objectId);
+        failure.put(
+            FAILURE_REASON_KEY,
+            SDMUtils.getErrorMessage("INVALID_SECONDARY_PROPERTIES_FOR_COPY_PREFIX")
+                + String.join(", ", invalidProperties)
+                + SDMUtils.getErrorMessage("INVALID_SECONDARY_PROPERTIES_FOR_COPY_SUFFIX"));
+        failures.add(failure);
+      }
+    }
+    return failures;
+  }
+
+  /**
+   * Gets the list of invalid secondary properties for a single object from SDM. Returns empty list
+   * if all properties are valid or if metadata cannot be fetched
+   */
+  private List<String> getInvalidPropertiesForObject(
+      String objectId,
+      Set<String> customPropertiesInSDM,
+      List<String> validSecondaryProperties,
+      SDMCredentials sdmCredentials,
+      Boolean isSystemUser) {
+    try {
+      JSONObject sdmMetadata = sdmService.getObject(objectId, sdmCredentials, isSystemUser);
+      if (sdmMetadata == null || !sdmMetadata.has("succinctProperties")) {
+        return Collections.emptyList();
+      }
+      JSONObject succinctProperties = sdmMetadata.getJSONObject("succinctProperties");
+      Set<String> sdmResponseProperties = new HashSet<>(succinctProperties.keySet());
+
+      List<String> invalidProperties = new ArrayList<>();
+      for (String targetSdmProperty : customPropertiesInSDM) {
+        if (sdmResponseProperties.contains(targetSdmProperty)
+            && !validSecondaryProperties.contains(targetSdmProperty)) {
+          invalidProperties.add(targetSdmProperty);
+        }
+      }
+      return invalidProperties;
+    } catch (IOException e) {
+      logger.error(
+          "Copy validation - Failed to fetch metadata for attachment {}: {}",
+          objectId,
+          e.getMessage());
+      return Collections.emptyList();
+    }
+  }
+
+  /** Builds and emits a warning message for copy failures */
+  private void buildAndWarnCopyFailures(
+      List<Map<String, String>> copyFailures, AttachmentCopyEventContext context) {
+    StringBuilder warningMessage =
+        new StringBuilder(SDMUtils.getErrorMessage("FAILED_TO_COPY_ATTACHMENTS_PREFIX"));
+    for (Map<String, String> failure : copyFailures) {
+      warningMessage
+          .append("- ObjectId: ")
+          .append(failure.get(OBJECT_ID_KEY))
+          .append(", Reason: ")
+          .append(failure.get(FAILURE_REASON_KEY))
+          .append("\n");
+    }
+    context.getMessages().warn(warningMessage.toString());
+  }
+
   /**
    * Moves attachments from source entity to target entity in SDM. Executes moves in parallel,
    * updates database records, and cleans up source metadata. If any step fails, the operation is
diff --git a/sdm/src/test/java/unit/com/sap/cds/sdm/service/handler/SDMCustomServiceHandlerTest.java b/sdm/src/test/java/unit/com/sap/cds/sdm/service/handler/SDMCustomServiceHandlerTest.java
index 437410755..d992c9a86 100644
--- a/sdm/src/test/java/unit/com/sap/cds/sdm/service/handler/SDMCustomServiceHandlerTest.java
+++ b/sdm/src/test/java/unit/com/sap/cds/sdm/service/handler/SDMCustomServiceHandlerTest.java
@@ -325,6 +325,172 @@ void testCopyAttachments_AttachmentCopyFails_FolderExists_AttachmentsDeleted()
     assertTrue(ex.getMessage().contains("Copy failed"));
   }
 
+  @Test
+  void testCopyAttachments_InvalidSecondaryProperty_BlocksCopy() throws IOException {
+    // Mock SDMCredentials
+    SDMCredentials sdmCredentials = mock(SDMCredentials.class);
+    when(tokenHandler.getSDMCredentials()).thenReturn(sdmCredentials);
+
+    // Mock folder id retrieval
+    when(sdmService.getFolderIdByPath(any(), any(), any(), anyBoolean())).thenReturn(FOLDER_ID);
+
+    // Create mock context with custom property annotations on the entity
+    AttachmentCopyEventContext context = createMockContextWithCustomProperties();
+    when(context.getObjectIds()).thenReturn(List.of(OBJECT_ID));
+
+    // Mock secondary types and valid secondary properties from SDM
+    when(sdmService.getSecondaryTypes(any(), any(), anyBoolean()))
+        .thenReturn(List.of("secondaryType1"));
+    when(sdmService.getValidSecondaryProperties(any(), any(), any(), anyBoolean()))
+        .thenReturn(List.of("validProp1", "validProp2"));
+
+    // Mock getObject: SDM response contains "invalidCustomProp" which is NOT in valid list
+    JSONObject sdmMetadata = new JSONObject();
+    JSONObject succinctProperties = new JSONObject();
+    succinctProperties.put("cmis:name", "test.pdf");
+    succinctProperties.put("invalidCustomProp", "someValue");
+    sdmMetadata.put("succinctProperties", succinctProperties);
+    when(sdmService.getObject(eq(OBJECT_ID), any(), anyBoolean())).thenReturn(sdmMetadata);
+
+    // Act
+    sdmCustomServiceHandler.copyAttachments(context);
+
+    // Assert: copy should be blocked entirely, no copy operation performed
+    verify(sdmService, never())
+        .copyAttachment(any(), any(SDMCredentials.class), anyBoolean(), any());
+    // Warning message should be issued
+    verify(context.getMessages(), times(1)).warn(any(String.class));
+    verify(context, times(1)).setCompleted();
+  }
+
+  @Test
+  void testCopyAttachments_MixedValidAndInvalidSecondaryProps_CopiesValidRejectsInvalid()
+      throws IOException {
+    // Mock SDMCredentials
+    SDMCredentials sdmCredentials = mock(SDMCredentials.class);
+    when(tokenHandler.getSDMCredentials()).thenReturn(sdmCredentials);
+
+    // Mock folder id retrieval
+    when(sdmService.getFolderIdByPath(any(), any(), any(), anyBoolean())).thenReturn(FOLDER_ID);
+
+    String validObjectId = "validObjectId";
+    String invalidObjectId = "invalidObjectId";
+
+    // Create mock context with custom property annotations
+    AttachmentCopyEventContext context = createMockContextWithCustomProperties();
+    when(context.getObjectIds()).thenReturn(List.of(validObjectId, invalidObjectId));
+
+    // Mock secondary types and valid secondary properties
+    when(sdmService.getSecondaryTypes(any(), any(), anyBoolean()))
+        .thenReturn(List.of("secondaryType1"));
+    when(sdmService.getValidSecondaryProperties(any(), any(), any(), anyBoolean()))
+        .thenReturn(List.of("validProp1", "validProp2"));
+
+    // Mock getObject for valid attachment (does NOT have "invalidCustomProp" in response)
+    JSONObject validMetadata = new JSONObject();
+    JSONObject validProps = new JSONObject();
+    validProps.put("cmis:name", "valid.pdf");
+    validProps.put("validProp1", "someValue");
+    validMetadata.put("succinctProperties", validProps);
+    when(sdmService.getObject(eq(validObjectId), any(), anyBoolean())).thenReturn(validMetadata);
+
+    // Mock getObject for invalid attachment (HAS "invalidCustomProp" which is NOT in valid list)
+    JSONObject invalidMetadata = new JSONObject();
+    JSONObject invalidProps = new JSONObject();
+    invalidProps.put("cmis:name", "invalid.pdf");
+    invalidProps.put("invalidCustomProp", "someValue");
+    invalidMetadata.put("succinctProperties", invalidProps);
+    when(sdmService.getObject(eq(invalidObjectId), any(), anyBoolean()))
+        .thenReturn(invalidMetadata);
+
+    // Mock attachment metadata and copy for the valid attachment
+    CmisDocument cmisDocument = new CmisDocument();
+    cmisDocument.setType("sap-icon://document");
+    when(dbQuery.getAttachmentForObjectID(any(), any(), any(AttachmentCopyEventContext.class)))
+        .thenReturn(cmisDocument);
+
+    Map<String, String> attachmentData = new HashMap<>();
+    attachmentData.put("cmis:name", "valid.pdf");
+    attachmentData.put("cmis:contentStreamMimeType", "application/pdf");
+    attachmentData.put("cmis:objectId", "newCopiedObjectId");
+    when(sdmService.copyAttachment(any(), any(SDMCredentials.class), anyBoolean(), any()))
+        .thenReturn(attachmentData);
+
+    // Act
+    sdmCustomServiceHandler.copyAttachments(context);
+
+    // Assert: valid attachment should be copied, invalid one should be warned about
+    verify(sdmService, times(1))
+        .copyAttachment(any(), any(SDMCredentials.class), anyBoolean(), any());
+    verify(context.getMessages(), times(1)).warn(any(String.class));
+    verify(draftService, times(1)).newDraft(any());
+    verify(context, times(1)).setCompleted();
+  }
+
+  private AttachmentCopyEventContext createMockContextWithCustomProperties() {
+    AttachmentCopyEventContext context = mock(AttachmentCopyEventContext.class);
+    CdsElement mockAssociationElement = mock(CdsElement.class);
+    CdsAssociationType mockAssociationType = mock(CdsAssociationType.class);
+    CqnElementRef mockCqnElementRef = mock(CqnElementRef.class);
+
+    when(context.getParentEntity()).thenReturn("prefix.someIdentifier." + FACET);
+    when(context.getCompositionName()).thenReturn(FACET);
+    when(context.getUpId()).thenReturn(UP_ID);
+    when(context.getSystemUser()).thenReturn(true);
+    when(context.getObjectIds()).thenReturn(List.of(OBJECT_ID));
+
+    // Mock CdsModel and relevant entities and associations
+    CdsModel model = mock(CdsModel.class);
+    CdsEntity parentEntity = mock(CdsEntity.class);
+    CdsEntity draftEntity = mock(CdsEntity.class);
+    CdsEntity targetEntity = mock(CdsEntity.class);
+    CdsEntity compositionEntity = mock(CdsEntity.class);
+
+    // Mock composition element and its type
+    CdsElement compositionElement = mock(CdsElement.class);
+    CdsAssociationType compositionType = mock(CdsAssociationType.class);
+
+    // Setup expected behavior for model and parent entity
+    when(context.getModel()).thenReturn(model);
+    when(model.findEntity("prefix.someIdentifier." + FACET)).thenReturn(Optional.of(parentEntity));
+    when(model.findEntity("prefix.someIdentifier." + FACET + "." + FACET))
+        .thenReturn(Optional.of(compositionEntity));
+    when(model.findEntity(endsWith("_drafts"))).thenReturn(Optional.of(draftEntity));
+
+    // Mock the composition entity with a custom property annotation
+    CdsElement customPropertyElement = mock(CdsElement.class);
+    com.sap.cds.reflect.CdsAnnotation<Object> nameAnnotation =
+        mock(com.sap.cds.reflect.CdsAnnotation.class);
+    com.sap.cds.reflect.CdsType elementType = mock(com.sap.cds.reflect.CdsType.class);
+    when(elementType.isAssociation()).thenReturn(false);
+    when(customPropertyElement.getType()).thenReturn(elementType);
+    when(customPropertyElement.getName()).thenReturn("customField");
+    when(customPropertyElement.findAnnotation("SDM.Attachments.AdditionalProperty.name"))
+        .thenReturn(Optional.of(nameAnnotation));
+    when(nameAnnotation.getValue()).thenReturn("invalidCustomProp");
+    when(compositionEntity.elements()).thenReturn(Stream.of(customPropertyElement));
+
+    // Mock the composition element in parent entity
+    when(parentEntity.findElement(FACET)).thenReturn(Optional.of(compositionElement));
+    when(compositionElement.getType()).thenReturn(compositionType);
+    when(compositionType.isAssociation()).thenReturn(true);
+    when(compositionType.getTarget()).thenReturn(targetEntity);
+    when(targetEntity.getQualifiedName()).thenReturn("target.entity.name");
+
+    // Mock the draft entity's up_ association
+    when(draftEntity.findAssociation("up_")).thenReturn(Optional.of(mockAssociationElement));
+    when(mockAssociationElement.getType()).thenReturn(mockAssociationType);
+    when(mockAssociationType.refs()).thenReturn(Stream.of(mockCqnElementRef));
+    when(mockCqnElementRef.path()).thenReturn("ID");
+
+    // Mock messages
+    com.sap.cds.services.messages.Messages messages =
+        mock(com.sap.cds.services.messages.Messages.class);
+    when(context.getMessages()).thenReturn(messages);
+
+    return context;
+  }
+
   private AttachmentCopyEventContext createMockContext() {
     AttachmentCopyEventContext context = mock(AttachmentCopyEventContext.class);
     CdsElement mockAssociationElement = mock(CdsElement.class);