The Open Redirect: Club-OS detection rule identifies emails where links to Club-OS may exploit open redirect vulnerabilities. The rule incorporates multiple conditions that examine the structure and parameters of URLs within any message body, particularly focusing on the domain 'club-os.com' and the presence of certain keywords in the URL path and query parameters. Specifically, it checks for the presence of 'click' in the path and 'target=' in the query parameters while ensuring that certain conditions are not met that would indicate the links are benign or trusted, such as checks against high-trust sender domains or predefined hash lookup values. The aim is to flag potential credential phishing or malware/ransomware attacks via the exploitation of open redirects, particularly in unsolicited or potentially malicious messaging.