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NibbleBlog 4.0.3 Shell Upload

Posted on 04 September 2015

NibbleBlog 4.0.3: Code Execution
Security Advisory – Curesec Research Team

1. Introduction

Affected Product: NibbleBlog 4.0.3
Fixed in: not fixed
Fixed Version Link: n/a
Vendor Contact: Website: http://www.nibbleblog.com/
Vulnerability Type: Code Execution
Remote Exploitable: Yes
Reported to vendor: 07/21/2015
Disclosed to public: 09/01/2015
Release mode: Full Disclosure
CVE: n/a
Credits Tim Coen of Curesec GmbH

2. Vulnerability Description

When uploading image files via the "My image" plugin - which is
delivered with NibbleBlog by default - , NibbleBlog 4.0.3 keeps the
original extension of uploaded files. This extension or the actual file
type are not checked, thus it is possible to upload PHP files and gain
code execution.

Please note that admin credentials are required.

3. Proof of Concept

 Obtain Admin credentials (for example via Phishing via XSS which can
be gained via CSRF, see advisory about CSRF in NibbleBlog 4.0.3)
 Activate My image plugin by visiting
http://localhost/nibbleblog/admin.php?controller=plugins&action=install&plugin=my_image
 Upload PHP shell, ignore warnings
 Visit
http://localhost/nibbleblog/content/private/plugins/my_image/image.php.
This is the default name of images uploaded via the plugin.

4. Code

 if( $plugin->init_db() )
 {
 // upload files
 foreach($_FILES as $field_name=>$file)
 {
 $extension = strtolower(pathinfo($file['name'],
PATHINFO_EXTENSION));
 $destination = PATH_PLUGINS_DB.$plugin->get_dir_name();
 $complete = $destination.'/'.$field_name.'.'.$extension;

 // Upload the new file and move
 if(move_uploaded_file($file["tmp_name"], $complete))
 {
 // Resize images if requested by the plugin
 if(isset($_POST[$field_name.'_resize']))
 {
 $width =
isset($_POST[$field_name.'_width'])?$_POST[$field_name.'_width']:200;
 $height =
isset($_POST[$field_name.'_height'])?$_POST[$field_name.'_height']:200;
 $option =
isset($_POST[$field_name.'_option'])?$_POST[$field_name.'_option']:'auto';
 $quality =
isset($_POST[$field_name.'_quality'])?$_POST[$field_name.'_quality']:100;

 $Resize->setImage($complete, $width, $height, $option);
 $Resize->saveImage($complete, $quality, true);
 }
 }
 }

 unset($_POST['plugin']);

 // update fields
 $plugin->set_fields_db($_POST);

 Session::set_alert($_LANG['CHANGES_HAS_BEEN_SAVED_SUCCESSFULLY']);
 }
 }

5. Solution

This issue was not fixed by the vendor.

6. Report Timeline

07/21/2015 Informed Vendor about Issue
07/22/2015 Vendor Replied
08/18/2015 Reminded Vendor of release date (no reply)
09/01/2015 Disclosed to public

7. Blog Reference
http://blog.curesec.com/article/blog/NibbleBlog-403-Code-Execution-47.html

 

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