This is a malicious request, but it's not trying to exploit a vulnerability. It's trying to generate a 404 page, in order to determine what kind of web server or CMS you're running, by identifying tokens in the page source. Error pages often specify their CMS name and version, or the web server name and version, so it's an easy target for recon.
Best advice I can give you is to keep everything patched, and make sure your firewall rules are properly configured. Primary targets are likely to be your CMS and web server, but your OS is important to patch too.
If you've got a few IPs that constantly do it, and you're certain they're not valid customers, feel free to block them for a few weeks to see if they remain persistent.