Hardening and Security Guidance¶
ownCloud aims to ship with secure defaults that do not need to get modified by administrators. However, in some cases some additional security hardening can only be applied in scenarios were the administrator have complete control over the ownCloud instance.
This document lists some security hardenings which require manual interaction by administrators. The whole document content is based on the assumption that you run ownCloud Server on Apache2 on a Linux environment.
Note
ownCloud will warn you in the administration interface if some critical security-relevant options are missing. However, it is still up to the server administrator to review and maintain system security.
Limit on Password Length¶
ownCloud uses the bcrypt algorithm and thus for security and performance reasons, e.g. Denial of Service as CPU demand increases exponentially, it only verifies the first 72 characters of passwords. This applies to all passwords that you use in ownCloud: user passwords, passwords on link shares, and passwords on external shares.
Operating system¶
Give PHP read accesss to /dev/urandom¶
ownCloud uses a RFC 4086 (“Randomness Requirements for Security”) compliant mixer to generate cryptographically secure pseudo-random numbers. This means that when generating a random number ownCloud will request multiple random numbers from different sources and derive from these the final random number.
The random number generation also tries to request random numbers from /dev/urandom, thus it is highly recommended to configure your setup in such a way that PHP is able to read random data from it. Not granting PHP access to /dev/urandom may make your random numbers predictable and may make your ownCloud instance insecure as attackers might predict password reset tokens or other sensitive data.
Note
When having an open_basedir configured within your php.ini make sure to include the folder /dev.
Enable hardening modules such as SELinux¶
It is highly recommend to enable hardening modules such as SELinux where possible. See SELinux Configuration to learn more about SELinux.
Use newest PHP version¶
Some security features and hardenings in PHP are only available in the latest PHP release and thus it is recommended to run the latest PHP version. You can find the latest version on http://php.net/.
Some Linux distributions backport security patches, but this is not reliable as some get missed, or the backports are years late. It is always best to run the latest PHP version.
Deployment¶
Move data directory outside of the web root¶
It is highly recommended to move the data directory (where ownCloud stores its data) outside of the web root (i.e. outside of /var/www) It is possible to do this by moving the folder manually, and then adjusting the 'datadirectory' parameter in config.php.
Disable preview image generation¶
ownCloud is able to generate preview images of common filetypes such as images or text files. By default the preview generation for some file types that we consider secure enough for deployment is enabled by default. However, administrators should be aware that these previews are generated using PHP libraries written in C which might be vulnerable to vulnerable attack vectors.
For high security deployments we recommend disabling the preview generation by setting the enable_previews switch to false in config.php. As an administrator you are also able to manage which preview providers are enabled by modifying the enabledPreviewProviders option switch.
Use HTTPS¶
Using ownCloud without using an encrypted HTTPS connection might allow attackers in a man-in-the-middle (MITM) situation to intercept your users data and passwords. Thus ownCloud always recommends to setup ownCloud behind HTTPS.
How to setup HTTPS on your web server depends on your setup, we recommend to check your distribution’s vendor information on how to configure and setup HTTPS.
Redirect all unencrypted traffic to HTTPS¶
To redirect all HTTP traffic to HTTPS administrators are encouraged to issue a permanent redirect using the 301 status code, when using Apache this can be achieved by a setting such as the following in the Apache VirtualHosts config:
<VirtualHost *:80>
ServerName cloud.owncloud.com
Redirect permanent / https://cloud.owncloud.com/
</VirtualHost>
Enable HTTP Strict Transport Security¶
While redirecting all traffic to HTTPS is already a good start it will often not completely prevent man-in-the-middle attacks for a regular user. Thus administrators are encouraged to set the HTTP Strict Transport Security header which will instruct browsers to not allow any connection to the ownCloud instance anymore using HTTPS and a invalid certificate warning will often not be able to get bypassed.
This can be achieved by setting the following settings within the Apache VirtualHost file:
<VirtualHost *:443>
ServerName cloud.owncloud.com
Header always add Strict-Transport-Security "max-age=15768000; includeSubDomains; preload"
</VirtualHost>
Be aware that above policy will also apply for all subdomains, if you don’t have HTTPS properly configured on all subdomains you mut remove the includeSubdomains part.
Furthermore it shall be noted that this requires that the mod_headers extension is installed.
Proper SSL configuration¶
Default SSL configurations by web servers are often not state of the art and require fine-tuning for an optimal performance and security experience. The available SSL ciphers and options depends completely on your environment and thus giving a generic recommendation is not really possible.
We recommend to use the Mozilla SSL Configuration Generator to generate a suitable configuration suited for your environment, furthermore the free Qualys SSL Labs Tests give a good guidance whether the SSL server was correctly configured.
Use a dedicated domain for ownCloud¶
Administrators are encouraged to install ownCloud on a dedicated domain such as cloud.domain.tld instead of domain.tld to gain all the benefits offered by the Same-Origin-Policy.