diff --git a/common/framework/Storage.php b/common/framework/Storage.php
index 6637c5cc0..20ea4e04f 100644
--- a/common/framework/Storage.php
+++ b/common/framework/Storage.php
@@ -873,6 +873,45 @@ class Storage
 		}
 	}
 
+	/**
+	 * Prevent access to a directory by creating .htaccess and index.html files in it.
+	 *
+	 * This is a best-effort measure only, and depends on web server configuration.
+	 * It is recommended to use proper server configuration to protect sensitive directories.
+	 *
+	 * @param string $dirname
+	 * @return bool
+	 */
+	public static function protectDirectory(string $dirname): bool
+	{
+		$dirname = rtrim($dirname, '/\\');
+		if (!self::isDirectory($dirname) || !self::isWritable($dirname))
+		{
+			return false;
+		}
+
+		$result = self::write($dirname . '/index.html', '');
+		if (!$result)
+		{
+			return false;
+		}
+		$result = self::write($dirname . '/.htaccess', preg_replace('/\\t/', '', <<<END
+			<IfModule authz_core_module>
+				Require all denied
+			</IfModule>
+			<IfModule !authz_core_module>
+				Order deny,allow
+				Deny from all
+			</IfModule>
+		END));
+		if (!$result)
+		{
+			return false;
+		}
+
+		return true;
+	}
+
 	/**
 	 * Get the current umask.
 	 *
diff --git a/modules/admin/controllers/systemconfig/Advanced.php b/modules/admin/controllers/systemconfig/Advanced.php
index 8622d1599..0f497fb80 100644
--- a/modules/admin/controllers/systemconfig/Advanced.php
+++ b/modules/admin/controllers/systemconfig/Advanced.php
@@ -76,7 +76,7 @@ class Advanced extends Base
 		// Thumbnail settings
 		$oDocumentModel = getModel('document');
 		$config = $oDocumentModel->getDocumentConfig();
-		Context::set('thumbnail_target', $config->thumbnail_target ?: 'all');
+		Context::set('thumbnail_target', $config->thumbnail_target ?: 'attachment');
 		Context::set('thumbnail_type', $config->thumbnail_type ?: 'fill');
 		Context::set('thumbnail_quality', $config->thumbnail_quality ?: 75);
 		if ($config->thumbnail_type === 'none')
@@ -190,7 +190,7 @@ class Advanced extends Base
 		// Thumbnail settings
 		$oDocumentModel = getModel('document');
 		$document_config = $oDocumentModel->getDocumentConfig();
-		$document_config->thumbnail_target = $vars->thumbnail_target ?: 'all';
+		$document_config->thumbnail_target = $vars->thumbnail_target ?: 'attachment';
 		$document_config->thumbnail_type = $vars->thumbnail_type ?: 'fill';
 		$document_config->thumbnail_quality = intval($vars->thumbnail_quality) ?: 75;
 		$oModuleController = getController('module');
diff --git a/modules/admin/lang/en.php b/modules/admin/lang/en.php
index e62c2c512..5b00752d3 100644
--- a/modules/admin/lang/en.php
+++ b/modules/admin/lang/en.php
@@ -338,8 +338,9 @@ $lang->mobile_viewport = 'Mobile viewport Setting';
 $lang->about_mobile_viewport = 'The settings entered above will be output in a &lt;meta name=&quot;viewport&quot;&gt; tag for mobile visitors.';
 $lang->restore_default_viewport = 'Restore Default';
 $lang->thumbnail_target = 'Extract Thumbnail From';
-$lang->thumbnail_target_all = 'All images';
+$lang->thumbnail_target_content = 'All embedded images, including external images';
 $lang->thumbnail_target_attachment = 'Attached images only';
+$lang->about_thumbnail_target = 'Using external images to generate thumbnails may cause various issues with respect to page load speed, copyright, and security. Please be careful.';
 $lang->thumbnail_type = 'Thumbnail Type';
 $lang->input_header_script = 'Header Script';
 $lang->detail_input_header_script = 'Content added here will be printed at the top of every page, except the admin module.';
diff --git a/modules/admin/lang/ko.php b/modules/admin/lang/ko.php
index d458a4e22..6ced528eb 100644
--- a/modules/admin/lang/ko.php
+++ b/modules/admin/lang/ko.php
@@ -334,8 +334,9 @@ $lang->mobile_viewport = '모바일 viewport 설정';
 $lang->about_mobile_viewport = '모바일 접속시 여기 입력한 내용이 &lt;meta name=&quot;viewport&quot;&gt; 태그로 출력됩니다.';
 $lang->restore_default_viewport = '기본값 복원';
 $lang->thumbnail_target = '썸네일 생성 대상';
-$lang->thumbnail_target_all = '모든 이미지 (외부 이미지 포함)';
+$lang->thumbnail_target_content = '모든 이미지 (외부 이미지 포함)';
 $lang->thumbnail_target_attachment = '첨부된 이미지';
+$lang->about_thumbnail_target = '외부 이미지를 사용하여 썸네일을 생성하는 경우 페이지 로딩 속도, 저작권, 보안 등 다양한 문제가 발생할 수 있으니 주의하시기 바랍니다.';
 $lang->thumbnail_type = '썸네일 생성 방식';
 $lang->input_header_script = '상단(헤더) 스크립트';
 $lang->detail_input_header_script = '모든 페이지의 최상단에 코드를 삽입합니다. 관리자 화면에는 적용되지 않습니다.';
diff --git a/modules/admin/tpl/config_advanced.html b/modules/admin/tpl/config_advanced.html
index 7c4540f59..c1c158476 100644
--- a/modules/admin/tpl/config_advanced.html
+++ b/modules/admin/tpl/config_advanced.html
@@ -126,18 +126,19 @@
 		<div class="x_control-group">
 			<label class="x_control-label">{$lang->thumbnail_target}</label>
 			<div class="x_controls">
-				<label for="thumbnail_target_all" class="x_inline">
-					<input type="radio" name="thumbnail_target" id="thumbnail_target_all" value="all" checked="checked"|cond="$thumbnail_target == 'all' || !$thumbnail_target" />
-					{$lang->thumbnail_target_all}
-				</label>
 				<label for="thumbnail_target_attachment" class="x_inline">
-					<input type="radio" name="thumbnail_target" id="thumbnail_target_attachment" value="attachment" checked="checked"|cond="$thumbnail_target == 'attachment'" />
+					<input type="radio" name="thumbnail_target" id="thumbnail_target_attachment" value="attachment" checked="checked"|cond="$thumbnail_target == 'attachment' || !$thumbnail_target" />
 					{$lang->thumbnail_target_attachment}
 				</label>
+				<label for="thumbnail_target_content" class="x_inline">
+					<input type="radio" name="thumbnail_target" id="thumbnail_target_content" value="content" checked="checked"|cond="$thumbnail_target == 'content'" />
+					{$lang->thumbnail_target_content}
+				</label>
 				<label for="thumbnail_target_none" class="x_inline">
 					<input type="radio" name="thumbnail_target" id="thumbnail_target_none" value="none" checked="checked"|cond="$thumbnail_target == 'none'" />
 					{$lang->thumbnail_none}
 				</label>
+				<p class="x_help-block">{$lang->about_thumbnail_target}</p>
 			</div>
 		</div>
 		<div class="x_control-group">
diff --git a/modules/comment/comment.item.php b/modules/comment/comment.item.php
index d4acad199..1af663786 100644
--- a/modules/comment/comment.item.php
+++ b/modules/comment/comment.item.php
@@ -924,28 +924,34 @@ class CommentItem extends BaseObject
 						$target_src = Context::getRequestUri().$target_src;
 					}
 
-					$tmp_file = sprintf('./files/cache/tmp/%d', md5(rand(111111, 999999) . $this->comment_srl));
-					if(!is_dir('./files/cache/tmp'))
+					$tmp_file = sprintf('./files/cache/tmp/%s', Rhymix\Framework\Security::getRandom(32));
+					if (!Rhymix\Framework\Storage::exists(\RX_BASEDIR . 'files/cache/tmp'))
 					{
-						FileHandler::makeDir('./files/cache/tmp');
+						Rhymix\Framework\Storage::createDirectory(\RX_BASEDIR . 'files/cache/tmp');
+					}
+					if (!Rhymix\Framework\Storage::exists(\RX_BASEDIR . 'files/cache/tmp/.htaccess'))
+					{
+						Rhymix\Framework\Storage::protectDirectory(\RX_BASEDIR . 'files/cache/tmp');
 					}
 					FileHandler::getRemoteFile($target_src, $tmp_file);
-					if(!file_exists($tmp_file))
+					if (!Rhymix\Framework\Storage::exists($tmp_file))
 					{
 						continue;
 					}
 					else
 					{
-						if($is_img = @getimagesize($tmp_file))
+						if ($is_img = @getimagesize($tmp_file))
 						{
 							list($_w, $_h, $_t, $_a) = $is_img;
 							if($_w < ($external_image_min_width) && ($height === 'auto' || $_h < ($external_image_min_height)))
 							{
+								Rhymix\Framework\Storage::delete($tmp_file);
 								continue;
 							}
 						}
 						else
 						{
+							Rhymix\Framework\Storage::delete($tmp_file);
 							continue;
 						}
 						$source_file = $tmp_file;
diff --git a/modules/document/document.item.php b/modules/document/document.item.php
index 7daa75828..38718714d 100644
--- a/modules/document/document.item.php
+++ b/modules/document/document.item.php
@@ -1257,28 +1257,34 @@ class DocumentItem extends BaseObject
 						$target_src = Context::getRequestUri().$target_src;
 					}
 
-					$tmp_file = sprintf('./files/cache/tmp/%d', md5(rand(111111,999999).$this->document_srl));
-					if(!is_dir('./files/cache/tmp'))
+					$tmp_file = sprintf('./files/cache/tmp/%s', Rhymix\Framework\Security::getRandom(32));
+					if (!Rhymix\Framework\Storage::exists(\RX_BASEDIR . 'files/cache/tmp'))
 					{
-						FileHandler::makeDir('./files/cache/tmp');
+						Rhymix\Framework\Storage::createDirectory(\RX_BASEDIR . 'files/cache/tmp');
+					}
+					if (!Rhymix\Framework\Storage::exists(\RX_BASEDIR . 'files/cache/tmp/.htaccess'))
+					{
+						Rhymix\Framework\Storage::protectDirectory(\RX_BASEDIR . 'files/cache/tmp');
 					}
 					FileHandler::getRemoteFile($target_src, $tmp_file);
-					if(!file_exists($tmp_file))
+					if (!Rhymix\Framework\Storage::exists($tmp_file))
 					{
 						continue;
 					}
 					else
 					{
-						if($is_img = @getimagesize($tmp_file))
+						if ($is_img = @getimagesize($tmp_file))
 						{
 							list($_w, $_h, $_t, $_a) = $is_img;
 							if($_w < ($external_image_min_width) && ($height === 'auto' || $_h < ($external_image_min_height)))
 							{
+								Rhymix\Framework\Storage::delete($tmp_file);
 								continue;
 							}
 						}
 						else
 						{
+							Rhymix\Framework\Storage::delete($tmp_file);
 							continue;
 						}
 						$source_file = $tmp_file;
diff --git a/modules/document/document.model.php b/modules/document/document.model.php
index 920e51083..b181b5c93 100644
--- a/modules/document/document.model.php
+++ b/modules/document/document.model.php
@@ -1036,9 +1036,9 @@ class DocumentModel extends Document
 		{
 			self::$_config = ModuleModel::getModuleConfig('document') ?: new stdClass;
 		}
-		if (!isset(self::$_config->thumbnail_target))
+		if (!isset(self::$_config->thumbnail_target) || self::$_config->thumbnail_target === 'all')
 		{
-			self::$_config->thumbnail_target = 'all';
+			self::$_config->thumbnail_target = 'attachment';
 		}
 		if (!isset(self::$_config->thumbnail_type))
 		{
diff --git a/tests/unit/framework/StorageTest.php b/tests/unit/framework/StorageTest.php
index 4b17ead0c..7c9e79bc2 100644
--- a/tests/unit/framework/StorageTest.php
+++ b/tests/unit/framework/StorageTest.php
@@ -346,6 +346,16 @@ class StorageTest extends \Codeception\Test\Unit
 		$this->assertFalse(Rhymix\Framework\Storage::deleteDirectory($nonexistent));
 	}
 
+	public function testProtectDirectory()
+	{
+		$dir = \RX_BASEDIR . 'tests/_output/protectdir';
+		mkdir($dir);
+		$this->assertTrue(Rhymix\Framework\Storage::protectDirectory($dir));
+		$this->assertTrue(file_exists($dir . '/index.html'));
+		$this->assertTrue(file_exists($dir . '/.htaccess'));
+		$this->assertStringContainsString('Require all denied', file_get_contents($dir . '/.htaccess'));
+	}
+
 	public function testDeleteDirectoryKeepRoot()
 	{
 		$sourcedir = \RX_BASEDIR . 'tests/_output/sourcedir';