This detection rule targets the exploitation of a known remote code execution (RCE) vulnerability identified as CVE-2021-40444, which affects Microsoft Windows systems through malicious Microsoft Office documents. Malicious actors can exploit this vulnerability by tricking users into opening documents that contain specially-crafted ActiveX controls aimed at leveraging the MSHTML engine. The specifics of the rule focus on identifying file attachments with certain characteristics, such as specific file extensions (macros or RTF) or ambiguous file types (e.g., an unknown type with a specific content type and file size). The detection mechanisms include various analyses like archive, content, file, macro, and OLE analysis to identify files with potential external relationships that may load remote OLE objects, which is consistent with payload delivery methods associated with this CVE. The rule emphasizes critical severity due to the inherent risks of RCE attacks, which can lead to severe system compromises. Detected files must match certain conditions to trigger an alert, ensuring tight monitoring of potentially malicious activity related to this vulnerability.