diff --git a/wcfsetup/install/files/lib/command/attachment/CopyAttachments.class.php b/wcfsetup/install/files/lib/command/attachment/CopyAttachments.class.php
new file mode 100644
index 00000000000..1f6bb48cb47
--- /dev/null
+++ b/wcfsetup/install/files/lib/command/attachment/CopyAttachments.class.php
@@ -0,0 +1,122 @@
+<?php
+
+namespace wcf\command\attachment;
+
+use wcf\data\attachment\Attachment;
+use wcf\data\attachment\AttachmentEditor;
+use wcf\data\attachment\AttachmentList;
+use wcf\data\file\thumbnail\FileThumbnailList;
+use wcf\data\object\type\ObjectType;
+use wcf\data\object\type\ObjectTypeCache;
+use wcf\system\file\processor\FileProcessor;
+
+/**
+ * Copies attachments from one object to another.
+ * Returns an array of old attachmentIDs as keys and new attachmentIDs as values.
+ *
+ * @author Olaf Braun
+ * @copyright 2001-2025 WoltLab GmbH
+ * @license GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @since 6.3
+ */
+final class CopyAttachments
+{
+    public function __construct(
+        private readonly string $sourceObjectType,
+        private readonly int $sourceObjectID,
+        private readonly string $targetObjectType,
+        private readonly int $targetObjectID,
+    ) {
+    }
+
+    /**
+     * @return array<int, int>
+     */
+    public function __invoke(): array
+    {
+        $sourceObjectType = ObjectTypeCache::getInstance()->getObjectTypeByName(
+            'com.woltlab.wcf.attachment.objectType',
+            $this->sourceObjectType
+        );
+        $targetObjectType = ObjectTypeCache::getInstance()->getObjectTypeByName(
+            'com.woltlab.wcf.attachment.objectType',
+            $this->targetObjectType
+        );
+
+        $attachments = $this->getAttachments($sourceObjectType, $this->sourceObjectID);
+
+        $newAttachmentIDs = [];
+        foreach ($attachments as $attachment) {
+            $newAttachment = $this->copyAttachment($targetObjectType, $attachment);
+
+            $newAttachmentIDs[$attachment->attachmentID] = $newAttachment->attachmentID;
+        }
+
+        return $newAttachmentIDs;
+    }
+
+    /**
+     * @return Attachment[]
+     */
+    private function getAttachments(ObjectType $sourceObjectType, int $sourceObjectID): array
+    {
+        $attachmentList = new AttachmentList();
+        $attachmentList->getConditionBuilder()->add("attachment.objectTypeID = ?", [$sourceObjectType->objectTypeID]);
+        $attachmentList->getConditionBuilder()->add("attachment.objectID = ?", [$sourceObjectID]);
+        $attachmentList->readObjects();
+
+        return $attachmentList->getObjects();
+    }
+
+    private function copyAttachment(ObjectType $targetObjectType, Attachment $oldAttachment): Attachment
+    {
+        $file = $oldAttachment->getFile();
+        $thumbnailID = null;
+        $tinyThumbnailID = null;
+
+        if ($file !== null) {
+            $file = FileProcessor::getInstance()->copy($file, 'com.woltlab.wcf.attachment');
+
+            if ($oldAttachment->thumbnailID !== null || $oldAttachment->tinyThumbnailID !== null) {
+                $thumbnailList = new FileThumbnailList();
+                $thumbnailList->getConditionBuilder()->add('fileID = ?', [$file->fileID]);
+                $thumbnailList->readObjects();
+
+                foreach ($thumbnailList->getObjects() as $thumbnail) {
+                    match ($thumbnail->identifier) {
+                        '' => $thumbnailID = $thumbnail->thumbnailID,
+                        'tiny' => $tinyThumbnailID = $thumbnail->thumbnailID,
+                    };
+                }
+            }
+        }
+
+        return AttachmentEditor::create([
+            'objectTypeID' => $targetObjectType->objectTypeID,
+            'objectID' => $this->targetObjectID,
+            'userID' => $oldAttachment->userID,
+            'filename' => $oldAttachment->filename,
+            'filesize' => $oldAttachment->filesize,
+            'fileType' => $oldAttachment->fileType,
+            'fileHash' => $oldAttachment->fileHash,
+            'isImage' => $oldAttachment->isImage,
+            'width' => $oldAttachment->width,
+            'height' => $oldAttachment->height,
+            'tinyThumbnailType' => $oldAttachment->tinyThumbnailType,
+            'tinyThumbnailSize' => $oldAttachment->tinyThumbnailSize,
+            'tinyThumbnailWidth' => $oldAttachment->tinyThumbnailWidth,
+            'tinyThumbnailHeight' => $oldAttachment->tinyThumbnailHeight,
+            'thumbnailType' => $oldAttachment->thumbnailType,
+            'thumbnailSize' => $oldAttachment->thumbnailSize,
+            'thumbnailWidth' => $oldAttachment->thumbnailWidth,
+            'thumbnailHeight' => $oldAttachment->thumbnailHeight,
+            'downloads' => $oldAttachment->downloads,
+            'lastDownloadTime' => $oldAttachment->lastDownloadTime,
+            'uploadTime' => $oldAttachment->uploadTime,
+            'showOrder' => $oldAttachment->showOrder,
+            'fileID' => $file?->fileID,
+            'thumbnailID' => $thumbnailID,
+            'tinyThumbnailID' => $tinyThumbnailID,
+        ]);
+    }
+}
diff --git a/wcfsetup/install/files/lib/data/attachment/AttachmentAction.class.php b/wcfsetup/install/files/lib/data/attachment/AttachmentAction.class.php
index 11bc81370fd..cafe8f8b726 100644
--- a/wcfsetup/install/files/lib/data/attachment/AttachmentAction.class.php
+++ b/wcfsetup/install/files/lib/data/attachment/AttachmentAction.class.php
@@ -2,12 +2,11 @@
 
 namespace wcf\data\attachment;
 
+use wcf\command\attachment\CopyAttachments;
 use wcf\data\AbstractDatabaseObjectAction;
-use wcf\data\file\thumbnail\FileThumbnailList;
 use wcf\data\object\type\ObjectTypeCache;
 use wcf\system\exception\PermissionDeniedException;
 use wcf\system\exception\UserInputException;
-use wcf\system\file\processor\FileProcessor;
 use wcf\system\WCF;
 
 /**
@@ -75,82 +74,18 @@ public function generateThumbnails()
      * Copies attachments from one object id to another.
      *
      * @return array{attachmentIDs: array<int, int>}
+     *
+     * @deprecated 6.3 use `CopyAttachments` instead.
      */
     public function copy()
     {
-        $sourceObjectType = ObjectTypeCache::getInstance()->getObjectTypeByName(
-            'com.woltlab.wcf.attachment.objectType',
-            $this->parameters['sourceObjectType']
-        );
-        $targetObjectType = ObjectTypeCache::getInstance()->getObjectTypeByName(
-            'com.woltlab.wcf.attachment.objectType',
-            $this->parameters['targetObjectType']
-        );
-
-        $attachmentList = new AttachmentList();
-        $attachmentList->getConditionBuilder()->add("attachment.objectTypeID = ?", [$sourceObjectType->objectTypeID]);
-        $attachmentList->getConditionBuilder()->add("attachment.objectID = ?", [$this->parameters['sourceObjectID']]);
-        $attachmentList->readObjects();
-
-        $newAttachmentIDs = [];
-        foreach ($attachmentList as $attachment) {
-            $file = $attachment->getFile();
-            if ($file !== null) {
-                $file = FileProcessor::getInstance()->copy($file, 'com.woltlab.wcf.attachment');
-
-                $thumbnailID = $tinyThumbnailID = null;
-                if ($attachment->thumbnailID !== null || $attachment->tinyThumbnailID !== null) {
-                    $thumbnailList = new FileThumbnailList();
-                    $thumbnailList->getConditionBuilder()->add('fileID = ?', [$file->fileID]);
-                    $thumbnailList->readObjects();
-
-                    foreach ($thumbnailList as $thumbnail) {
-                        switch ($thumbnail->identifier) {
-                            case '':
-                                $thumbnailID = $thumbnail->thumbnailID;
-                                break;
-
-                            case 'tiny':
-                                $tinyThumbnailID = $thumbnail->thumbnailID;
-                                break;
-                        }
-                    }
-                }
-            }
-
-            $newAttachment = AttachmentEditor::create([
-                'objectTypeID' => $targetObjectType->objectTypeID,
-                'objectID' => $this->parameters['targetObjectID'],
-                'userID' => $attachment->userID,
-                'filename' => $attachment->filename,
-                'filesize' => $attachment->filesize,
-                'fileType' => $attachment->fileType,
-                'fileHash' => $attachment->fileHash,
-                'isImage' => $attachment->isImage,
-                'width' => $attachment->width,
-                'height' => $attachment->height,
-                'tinyThumbnailType' => $attachment->tinyThumbnailType,
-                'tinyThumbnailSize' => $attachment->tinyThumbnailSize,
-                'tinyThumbnailWidth' => $attachment->tinyThumbnailWidth,
-                'tinyThumbnailHeight' => $attachment->tinyThumbnailHeight,
-                'thumbnailType' => $attachment->thumbnailType,
-                'thumbnailSize' => $attachment->thumbnailSize,
-                'thumbnailWidth' => $attachment->thumbnailWidth,
-                'thumbnailHeight' => $attachment->thumbnailHeight,
-                'downloads' => $attachment->downloads,
-                'lastDownloadTime' => $attachment->lastDownloadTime,
-                'uploadTime' => $attachment->uploadTime,
-                'showOrder' => $attachment->showOrder,
-                'fileID' => $file?->fileID,
-                'thumbnailID' => $thumbnailID ?? null,
-                'tinyThumbnailID' => $tinyThumbnailID ?? null,
-            ]);
-
-            $newAttachmentIDs[$attachment->attachmentID] = $newAttachment->attachmentID;
-        }
-
         return [
-            'attachmentIDs' => $newAttachmentIDs,
+            'attachmentIDs' => (new CopyAttachments(
+                $this->parameters['sourceObjectType'],
+                $this->parameters['sourceObjectID'],
+                $this->parameters['targetObjectType'],
+                $this->parameters['targetObjectID']
+            ))()
         ];
     }
 }