This detection rule is designed to identify potential HTML smuggling attacks that leverage the RC4 encryption algorithm within inline JavaScript. The mechanism involves passing malicious payloads disguised as HTML files, which can be decrypted at runtime using RC4. This type of attack is particularly concerning as it enables the eventual execution of potentially harmful scripts on the victim's system, facilitating credential phishing or the deployment of malware/ransomware. The rule triggers when attachments with specific file extensions (including .html, .htm, .shtml, .dhtml, or common archive formats) are detected. Additionally, it inspects the content of these files for strings that match a particular pattern indicative of the RC4 decryption process. The associated tactics and techniques include encryption, evasion, HTML smuggling, and scripting, which are prevalent in modern cyber threats. Various detection methods are employed, including archive and content analysis, highlighting the multi-faceted approach required to identify such sophisticated threats.