This threat detection rule identifies the use of SSL certificates that are blacklisted due to their association with malicious activities, such as malware distribution or command-and-control operations. Utilizing logs generated by Cisco Secure Firewall, the rule specifically checks the SHA1 fingerprint of SSL certificates against a maintained blacklist. By doing this, it can detect potentially harmful encrypted sessions, even when the corresponding domains or IPs vary. This is of particular concern as attackers frequently use self-signed or reused certificates across various malicious infrastructures. Successful detection could indicate ongoing beaconing activities, unauthorized malware downloads, or potential data exfiltration over secured channels like TLS/SSL.