How can I tell what version of FreeBSD my pfSense version is based on

From PFSenseDocs

Summary

How can I tell which version of FreeBSD pfSense is based on?

Solution

You can check the pfSense and FreeBSD Versions article for a table of versions in use, or follow these instructions:

• Check out the page regarding HOWTO enable SSH access or HOWTO execute commands via exec.php.
• Under Diagnostics -> Command, or at a SSH console, run the following:
  • uname -mrs