SMTP is the key: BPFDoor and AVERAT hitting the network edge

Overview Rapid7 tracked a set of Linux samples that blend into the software and device conventions of the telecom environments they target. The set spans a newly observed BPFDoor variant, a BPF Rekoobe build seen against South Korean targets, a dropper, and six builds of a Linux implant we track as AVERAT , deployed against Taiwanese appliances. Additionally, we provide source code details of the Rapid7 BPFDoor controller introduced in our April 2026 blog, Stealthy BPFDoor Variants are a Needle That Looks Like Hay .