There is a critical 0-Day exploit for Exchange already being exploited, which is pretty much the same as the "ProxyShell" vulnerability in March.
How can I check if the mitigation is already working with Snort or IPS rules?
There is also written (see "Temporary containment measures") how to create a rewrite rule to address the vulnerability, until a patch becomes available.
Just to clarify on the matter of "Could i be potentially be breached?".
If you think, there could be an attack ongoing or something odd is going on in your network / company, do not hesitate to contact an incident respond team. Every minute counts in such scenarios.
You will find Incident respond teams and services most likely on your government pages or you can contact Sophos Rapid Response. https://www.sophos.com/en-us/products/managed-threat-response/rapid-response