The use of DNS over HTTPS (DoH) for command and control communications is making it more difficult to track botnets, according to anti-spam nonprofit Spamhaus.
Spamhaus, which specializes in providing intel on spam and related threats, on Thursday reported seeing a 23% increase in new botnet command and control (C&C) servers in the last quarter of 2021.
However, the organization complained that the use of DoH “tilts the scales in the cybercriminals’ favor.”
The DoH protocol is designed to boost privacy and security by ensuring that DNS information is protected by encryption while it’s in transit. DoH has been increasingly adopted by major web browser makers, and even the NSA has advised businesses to use it.
However, DoH has been increasingly leveraged by cybercriminals as well. The first malware family to abuse DoH to secure communications was the GodLua backdoor, in 2019, and other threat actors have since turned to the protocol to hide their activities.
Spamhaus said on Thursday that the FluBot and TeamBot malware families were responsible for “an explosion in backdoor malware” in the third quarter of 2021. However, in the fourth quarter, they seemed to disappear completely.
The nonprofit says the two threats are still very much active, but it no longer has visibility due to their use of DoH, including DoH services provided by major companies such as Google and Alibaba.
The organization complained that since it no longer has visibility into FluBot and TeamBot DNS requests, it can no longer identify the IP addresses they use and add them to its block lists — these lists can be used by companies to block malicious traffic.
“Not only does DoH make hunting down miscreants even more challenging, but it also means that security products based around DNS monitoring and filtering could be less effective, which is far from ideal,” Spamhaus said. “Security issues are compounded due to major DoH providers not filtering harmful DNS resolutions of botnet, phishing or malware domains.”