diff --git a/lib/Service/FileService.php b/lib/Service/FileService.php
index 2112a30f1..2c5e359d3 100644
--- a/lib/Service/FileService.php
+++ b/lib/Service/FileService.php
@@ -27,10 +27,9 @@ use OCA\Deck\Db\Attachment;
 use OCA\Deck\Db\AttachmentMapper;
 use OCA\Deck\StatusException;
 use OCA\Deck\Exceptions\ConflictException;
-use OCP\AppFramework\Http\ContentSecurityPolicy;
-use OCP\AppFramework\Http\FileDisplayResponse;
 use OCP\AppFramework\Http\StreamResponse;
 use OCP\Files\IAppData;
+use OCP\Files\IMimeTypeDetector;
 use OCP\Files\IRootFolder;
 use OCP\Files\NotFoundException;
 use OCP\Files\NotPermittedException;
@@ -49,6 +48,7 @@ class FileService implements IAttachmentService {
 	private $rootFolder;
 	private $config;
 	private $attachmentMapper;
+	private $mimeTypeDetector;
 
 	public function __construct(
 		IL10N $l10n,
@@ -57,7 +57,8 @@ class FileService implements IAttachmentService {
 		ILogger $logger,
 		IRootFolder $rootFolder,
 		IConfig $config,
-		AttachmentMapper $attachmentMapper
+		AttachmentMapper $attachmentMapper,
+		IMimeTypeDetector $mimeTypeDetector
 	) {
 		$this->l10n = $l10n;
 		$this->appData = $appData;
@@ -66,6 +67,7 @@ class FileService implements IAttachmentService {
 		$this->rootFolder = $rootFolder;
 		$this->config = $config;
 		$this->attachmentMapper = $attachmentMapper;
+		$this->mimeTypeDetector = $mimeTypeDetector;
 	}
 
 	/**
@@ -225,27 +227,14 @@ class FileService implements IAttachmentService {
 
 	/**
 	 * @param Attachment $attachment
-	 * @return FileDisplayResponse|\OCP\AppFramework\Http\Response|StreamResponse
+	 * @return StreamResponse
 	 * @throws \Exception
 	 */
 	public function display(Attachment $attachment) {
 		$file = $this->getFileFromRootFolder($attachment);
-		if (method_exists($file, 'fopen')) {
-			$response = new StreamResponse($file->fopen('r'));
-			$response->addHeader('Content-Disposition', 'inline; filename="' . rawurldecode($file->getName()) . '"');
-		} else {
-			$response = new FileDisplayResponse($file);
-		}
-		// We need those since otherwise chrome won't show the PDF file with CSP rule object-src 'none'
-		// https://bugs.chromium.org/p/chromium/issues/detail?id=271452
-		$policy = new ContentSecurityPolicy();
-		$policy->addAllowedObjectDomain('\'self\'');
-		$policy->addAllowedObjectDomain('blob:');
-		$policy->addAllowedMediaDomain('\'self\'');
-		$policy->addAllowedMediaDomain('blob:');
-		$response->setContentSecurityPolicy($policy);
-
-		$response->addHeader('Content-Type', $file->getMimeType());
+		$response = new StreamResponse($file->fopen('rb'));
+		$response->addHeader('Content-Disposition', 'attachment; filename="' . rawurldecode($file->getName()) . '"');
+		$response->addHeader('Content-Type', $this->mimeTypeDetector->getSecureMimeType($file->getMimeType()));
 		return $response;
 	}
 
diff --git a/lib/Service/FilesAppService.php b/lib/Service/FilesAppService.php
index 089417900..ea6c06506 100644
--- a/lib/Service/FilesAppService.php
+++ b/lib/Service/FilesAppService.php
@@ -26,10 +26,9 @@ namespace OCA\Deck\Service;
 use OCA\Deck\Db\Attachment;
 use OCA\Deck\Sharing\DeckShareProvider;
 use OCA\Deck\StatusException;
-use OCP\AppFramework\Http\ContentSecurityPolicy;
-use OCP\AppFramework\Http\FileDisplayResponse;
 use OCP\AppFramework\Http\StreamResponse;
 use OCP\Constants;
+use OCP\Files\IMimeTypeDetector;
 use OCP\Files\IRootFolder;
 use OCP\Files\NotFoundException;
 use OCP\IDBConnection;
@@ -50,6 +49,7 @@ class FilesAppService implements IAttachmentService, ICustomAttachmentService {
 	private $l10n;
 	private $preview;
 	private $permissionService;
+	private $mimeTypeDetector;
 
 	public function __construct(
 		IRequest $request,
@@ -60,6 +60,7 @@ class FilesAppService implements IAttachmentService, ICustomAttachmentService {
 		DeckShareProvider $shareProvider,
 		IPreview $preview,
 		PermissionService $permissionService,
+		IMimeTypeDetector $mimeTypeDetector,
 		string $userId = null
 	) {
 		$this->request = $request;
@@ -70,6 +71,7 @@ class FilesAppService implements IAttachmentService, ICustomAttachmentService {
 		$this->shareManager = $shareManager;
 		$this->userId = $userId;
 		$this->preview = $preview;
+		$this->mimeTypeDetector = $mimeTypeDetector;
 	}
 
 	public function listAttachments(int $cardId): array {
@@ -147,22 +149,10 @@ class FilesAppService implements IAttachmentService, ICustomAttachmentService {
 		if ($file === null || $share->getSharedWith() !== (string)$attachment->getCardId()) {
 			throw new NotFoundException('File not found');
 		}
-		if (method_exists($file, 'fopen')) {
-			$response = new StreamResponse($file->fopen('r'));
-			$response->addHeader('Content-Disposition', 'inline; filename="' . rawurldecode($file->getName()) . '"');
-		} else {
-			$response = new FileDisplayResponse($file);
-		}
-		// We need those since otherwise chrome won't show the PDF file with CSP rule object-src 'none'
-		// https://bugs.chromium.org/p/chromium/issues/detail?id=271452
-		$policy = new ContentSecurityPolicy();
-		$policy->addAllowedObjectDomain('\'self\'');
-		$policy->addAllowedObjectDomain('blob:');
-		$policy->addAllowedMediaDomain('\'self\'');
-		$policy->addAllowedMediaDomain('blob:');
-		$response->setContentSecurityPolicy($policy);
 
-		$response->addHeader('Content-Type', $file->getMimeType());
+		$response = new StreamResponse($file->fopen('rb'));
+		$response->addHeader('Content-Disposition', 'attachment; filename="' . rawurldecode($file->getName()) . '"');
+		$response->addHeader('Content-Type', $this->mimeTypeDetector->getSecureMimeType($file->getMimeType()));
 		return $response;
 	}
 
diff --git a/tests/unit/Service/FileServiceTest.php b/tests/unit/Service/FileServiceTest.php
index e8662b775..a94dd8253 100644
--- a/tests/unit/Service/FileServiceTest.php
+++ b/tests/unit/Service/FileServiceTest.php
@@ -25,10 +25,10 @@ namespace OCA\Deck\Service;
 
 use OCA\Deck\Db\Attachment;
 use OCA\Deck\Db\AttachmentMapper;
-use OCP\AppFramework\Http\ContentSecurityPolicy;
 use OCP\AppFramework\Http\StreamResponse;
 use OCP\Files\Folder;
 use OCP\Files\IAppData;
+use OCP\Files\IMimeTypeDetector;
 use OCP\Files\IRootFolder;
 use OCP\Files\SimpleFS\ISimpleFile;
 use OCP\Files\SimpleFS\ISimpleFolder;
@@ -57,6 +57,8 @@ class FileServiceTest extends TestCase {
 	private $config;
 	/** @var AttachmentMapper|MockObject */
 	private $attachmentMapper;
+	/** @var IMimeTypeDetector|MockObject */
+	private $mimeTypeDetector;
 
 	public function setUp(): void {
 		parent::setUp();
@@ -67,7 +69,8 @@ class FileServiceTest extends TestCase {
 		$this->rootFolder = $this->createMock(IRootFolder::class);
 		$this->config = $this->createMock(IConfig::class);
 		$this->attachmentMapper = $this->createMock(AttachmentMapper::class);
-		$this->fileService = new FileService($this->l10n, $this->appData, $this->request, $this->logger, $this->rootFolder, $this->config, $this->attachmentMapper);
+		$this->mimeTypeDetector = $this->createMock(IMimeTypeDetector::class);
+		$this->fileService = new FileService($this->l10n, $this->appData, $this->request, $this->logger, $this->rootFolder, $this->config, $this->attachmentMapper, $this->mimeTypeDetector);
 	}
 
 	public function mockGetFolder($cardId) {
@@ -268,51 +271,13 @@ class FileServiceTest extends TestCase {
 		$file->expects($this->any())
 			->method('fopen')
 			->willReturn('fileresource');
+		$this->mimeTypeDetector->expects($this->once())
+			->method('getSecureMimeType')
+			->willReturn('image/jpeg');
 		$actual = $this->fileService->display($attachment);
 		$expected = new StreamResponse('fileresource');
 		$expected->addHeader('Content-Type', 'image/jpeg');
-		$expected->addHeader('Content-Disposition', 'inline; filename="' . rawurldecode($file->getName()) . '"');
-		$policy = new ContentSecurityPolicy();
-		$policy->addAllowedObjectDomain('\'self\'');
-		$policy->addAllowedObjectDomain('blob:');
-		$policy->addAllowedMediaDomain('\'self\'');
-		$policy->addAllowedMediaDomain('blob:');
-		$expected->setContentSecurityPolicy($policy);
-		$this->assertEquals($expected, $actual);
-	}
-
-	public function testDisplayPdf() {
-		$this->config->expects($this->once())
-			->method('getSystemValue')
-			->willReturn('123');
-		$appDataFolder = $this->createMock(Folder::class);
-		$deckAppDataFolder = $this->createMock(Folder::class);
-		$cardFolder = $this->createMock(Folder::class);
-		$this->rootFolder->expects($this->once())->method('get')->willReturn($appDataFolder);
-		$appDataFolder->expects($this->once())->method('get')->willReturn($deckAppDataFolder);
-		$deckAppDataFolder->expects($this->once())->method('get')->willReturn($cardFolder);
-		$attachment = $this->getAttachment();
-		$file = $this->createMock(\OCP\Files\File::class);
-		$cardFolder->expects($this->once())->method('get')->willReturn($file);
-		$file->expects($this->any())
-			->method('getMimeType')
-			->willReturn('application/pdf');
-		$file->expects($this->any())
-			->method('getName')
-			->willReturn('file1');
-		$file->expects($this->any())
-			->method('fopen')
-			->willReturn('fileresource');
-		$actual = $this->fileService->display($attachment);
-		$expected = new StreamResponse('fileresource');
-		$expected->addHeader('Content-Disposition', 'inline; filename="' . rawurldecode($file->getName()) . '"');
-		$expected->addHeader('Content-Type', 'application/pdf');
-		$policy = new ContentSecurityPolicy();
-		$policy->addAllowedObjectDomain('\'self\'');
-		$policy->addAllowedObjectDomain('blob:');
-		$policy->addAllowedMediaDomain('\'self\'');
-		$policy->addAllowedMediaDomain('blob:');
-		$expected->setContentSecurityPolicy($policy);
+		$expected->addHeader('Content-Disposition', 'attachment; filename="' . rawurldecode($file->getName()) . '"');
 		$this->assertEquals($expected, $actual);
 	}