Many cloud providers allow you access to a private network environment where you can exchange data with other instances or other services offered by the provider. The convenience of this access comes with a price: other instances can access your instance on the private network just as easily as they could on the public interface.

Here are some security tips for your private interfaces:

Disable the private interface
This one is pretty simple. If you have only one instance or server, and you don't need to communicate privately with any other instances, just disable the interface. Remember to configure your networking scripts to leave the interface disabled after reboots.

Use packet filtering
The actual mechanism will vary based on your operating system, but filtering packets is the one of the simplest ways to secure your private interface. You can take some different approaches with them, but I find the easiest method is to allow access from your other instances and reject all other traffic.

For additional security, you can limit access based on ports as well as source IP addresses. This could prevent an attacker from having easy access to your other instances if they're able to break into one of them.

Configure your daemons to listen on the appropriate interfaces
If there are services that don't need to be listening on the private network, don't allow them to listen on your private interface. For example, MySQL might need to listen on the private interface so the web server can talk to it, but apache won't need to listen on the private interface. This reduces the profile of your instance on the private network and makes it a less likely target for attack.

Use hosts.allow and hosts.deny
Many new systems administrators forget about how handy tcpwrappers can be for limiting access. If your firewall is down in error, host.allow and hosts.deny could be an extra layer of protection. It's important to ensure that the daemons you are attempting to control are build with tcpwrappers support. Daemons like sshd support it, but apache and MySQL do not.

Encrypt all traffic on the private network
Just because it's called a "private" network doesn't mean that your traffic can traverse the network privately. You should always err on the side of caution and encrypt all traffic traversing the private network. You can use ssh tunnels, stunnel, or the built-in SSL features found in most daemons.

This also brings up an important point: you should know how your provider's private network works. Are there safeguards to prevent sniffing? Could someone else possibly ARP spoof your instance's private IP addresses? Is your private network's subnet shared among many customers?

With all of that said, it's also very important to have proper change control policies so that administrators working after you are fully aware of the security measures in place and why they are important. This will ensure that all of the administrators on your instances will understand the security of the system and they should be able to make sensible adjustments later for future functionality.

Private network interfaces: the forgotten security hole is a post from: Major Hayden's Racker Hacker blog.

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Encrypted Swap Partitions and Non-root File Systems
Red Hat Enterprise Linux 5 now provides basic support for encrypted swap partitions and non-root file systems. To use these features, add the appropriate entries to /etc/crypttab and reference the created devices in /etc/fstab.

Below is a sample /etc/crypttab entry:

my_swap /dev/hdb1 /dev/urandom swap,cipher=aes-cbc-essiv:sha256
This creates the encrypted block device /dev/mapper/my_swap, which can be referenced in /etc/fstab.

Below is a sample /etc/crypttab entry for a file system volume:

my_volume /dev/hda5 /etc/volume_key cipher=aes-cbc-essiv:sha256
The /etc/volume_key file contains a plaintext encryption key. You can also specify none as the key file name; this configures the system to ask for the encryption key during boot instead.

It is recommended to use LUKS (Linux Unified Key Setup) for setting up file system volumes. To do this, follow these steps:

Create the encrypted volume using cryptsetup luksFormat.

Add the necessary entry to /etc/crypttab.

Set up the volume manually using cryptsetup luksOpen (or reboot).

Create a file system on the encrypted volume.

Add the necessary entry to /etc/fstab.

After scouring the Red Hat Enterprise Linux manuals and knowledge base, I couldn't find specific instructions to set it up. However, there was an article in the Red Hat Magazine that may help.

Encrypted filesystems and partitions on RHEL 5 is a post from: Major Hayden's Racker Hacker blog.

Thanks for following the blog via the RSS feed. Please don't copy my posts or quote portions of them without attribution.