unable to access files outside of site account

Operating System & Version
CloudLinux v7.9.0
cPanel & WHM Version
cPanel & WHM v104.0.7


Aug 7, 2014
cPanel Access Level
Reseller Owner
From within a site account I'm unable to access files outside of the account, and I can't find the WHM setting that manages that.
Here's the scenario:

account path: /home/mysite/
test file: /home/mysite/public_html/test.php
executable app: /usr/local/bin/myapp

In my test file I simply check for existence and executability:

$path = '/usr/local/bin/myapp';
echo file_exists($path);
echo is_executable($path);

Both checks fail. The file definitely exists and is definitely executable. I can run the file from the command line as root, but not as the mysite user.
I thought it might be an open_basedir issue, but that is not enabled on the account as far as I can see.

For reference, we're running:
Operating System: CloudLinux v7.9.0
Product: cPanel & WHM v104.0.7