structures

Cisco Talos has disclosed a new Windows implant called CLOSEDQUORUM, which operates without human operators by using four commercial large language models (LLMs) to autonomously decide on actions after deployment. The implant is a 16.4-megabyte executable that conducts reconnaissance on the target system and sends structured prompts to the LLMs, which respond with one of four actions: steal, inject, persist, or move. When the "steal" action is chosen, it simultaneously attacks three credential stores, extracting Windows credentials, browser passwords, and cryptocurrency wallet data. The "inject" action uses either Early Bird APC injection or process hollowing based on model recommendations. For persistence, it employs three overlapping mechanisms, including a Registry Run key, a scheduled task, and a WMI event subscription. To evade detection, CLOSEDQUORUM suppresses ETW telemetry and introduces delays before executing actions. It circumvents traditional command-and-control structures by calling legitimate API endpoints, making blocking these domains impractical. Talos introduced the CAIRN toolkit for detecting AI-integrated malware, which operates on metadata and employs rule-based detection. Unlike previous AI-assisted malware, CLOSEDQUORUM automates decision-making processes entirely, highlighting a significant evolution in malware capabilities. Security teams are advised to focus on behavioral detection strategies and utilize the YARA rule and CAIRN toolkit for identifying this threat.