Security researchers discovered a new attack they’re calling “Cloud Snooper” that uses innocent-looking requests to bypass the rules of many, if not most, firewalls.

SophosLabs launched an investigation into the Cloud Snooper campaign when it discovered an anomaly. Specifically, it found that a compromised Linux system with Amazon Web Services (AWS) security groups tuned only for inbound HTTP and HTTPS traffic was still listening for inbound connections on ports 2080/TCP and 2053/TCP. A closer look revealed a rootkit that helped attackers communicate with a backdoor.

Researchers at the security firm analyzed this activity and observed that the attackers had sent innocent-looking requests to the web server via other normal web servers in an attempt to avoid detection by a firewall. A listener picked up on those requests before they reached the web server and then sent a “reconstructed” command to the backdoor for the purpose of stealing sensitive data. The rootkit then disguised its communication once again to exfiltrate the information and ultimately send it back to a command-and-control (C&C) server operated by the attackers.

Firewall Bypasses A-Plenty

Cloud Snooper is not the first attack in which malicious actors have attempted to bypass firewall rules. Back in 2017, for instance, Microsoft warned of a new technique in which the PLATINUM group abused Intel’s Active Management Technology to bypass firewalls and other endpoint-based network monitoring tools.

In February 2018, NewSky Security spotted the DoubleDoor internet of things (IoT) botnet using two backdoor exploits to evade detection by a firewall. More recently, in August 2019, Proofpoint observed the SystemBC malware creating proxies on infected computers, paving the way for other malware payloads to bypass firewalls and similar tools.

How to Defend Against the Cloud Snooper Attack

To combat campaigns such as the Cloud Snooper attack described here, security professionals should start by investing in tools that can analyze network traffic in real time. This visibility is crucial for detecting unapproved devices as well as potential exfiltration of sensitive data. Additionally, infosec personnel should make sure their network’s “crown jewels” are configured to generate alerts individually so they can watch for anomalous behavior.