Explanation
The best rule to prevent ransomware that has not been seen before, without blocking other processes, is B.
This rule uses the following criteria:
Not listed application: This means that the application is not known by Carbon Black Cloud Endpoint Standard, and it has no reputation or signature. This can indicate a new or unknown malware that has not been detected by other methods.
Performs ransomware-like behavior: This means that the application is performing actions that are typical of ransomware, such as encrypting files, deleting backups, or displaying ransom notes. This can indicate a malicious intent and a high risk of data loss or damage.
Terminate process: This means that the application is stopped and removed from the endpoint, preventing it from completing its malicious actions or spreading to other devices. This can mitigate the impact and severity of the attack.
The other rules are not as effective or appropriate for preventing ransomware that has not been seen before, without blocking other processes. Rule A would only block adware or potentially unwanted programs (PUPs) that scrape memory of another process, which is not necessarily related to ransomware. Rule C would block any unknown malware that runs or is running, which is too broad and could affect legitimate applications that are not listed by Carbon Black. Rule D would block any not listed application that runs or is running, which is also too broad and could affect legitimate applications that are not listed by Carbon Black.
References: Carbon Black Cloud Endpoint Standard - Technical Overview, Best Practices: Endpoint Standard Blocking
& Isolation Rules, Endpoint Standard: How to add a SHA256 hash to Approved/Banned List