For the past week, domains associated with the massive Aisuru botnet have repeatedly usurped Amazon, Apple, Google and Microsoft in Cloudflare’s public ranking of the most frequently requested websites. Cloudflare responded by redacting Aisuru domain names from their top websites list. The chief executive at Cloudflare says Aisuru’s overlords are using the botnet to boost their malicious domain rankings, while simultaneously attacking the company’s domain name system (DNS) service.
Aisuru is a rapidly growing botnet comprising hundreds of thousands of hacked Internet of Things (IoT) devices, such as poorly secured Internet routers and security cameras. The botnet has increased in size and firepower significantly since its debut in 2024, demonstrating the ability to launch record distributed denial-of-service (DDoS) attacks nearing 30 terabits of data per second.
Until recently, Aisuru’s malicious code instructed all infected systems to use DNS servers from Google — specifically, the servers at 8.8.8.8. But in early October, Aisuru switched to invoking Cloudflare’s main DNS server — 1.1.1.1 — and over the past week domains used by Aisuru to control infected systems started populating Cloudflare’s top domain rankings.
As screenshots of Aisuru domains claiming two of the Top 10 positions ping-ponged across social media, many feared this was yet another sign that an already untamable botnet was running completely amok. One Aisuru botnet domain that sat prominently for days at #1 on the list was someone’s street address in Massachusetts followed by “.com”. Other Aisuru domains mimicked those belonging to major cloud providers.
Cloudflare tried to address these security, brand confusion and privacy concerns by partially redacting the malicious domains, and adding a warning at the top of its rankings:
“Note that the top 100 domains and trending domains lists include domains with organic activity as well as domains with emerging malicious behavior.”
Cloudflare CEO Matthew Prince told KrebsOnSecurity the company’s domain ranking system is fairly simplistic, and that it merely measures the volume of DNS queries to 1.1.1.1.
“The attacker is just generating a ton of requests, maybe to influence the ranking but also to attack our DNS service,” Prince said, adding that Cloudflare has heard reports of other large public DNS services seeing similar uptick in attacks. “We’re fixing the ranking to make it smarter. And, in the meantime, redacting any sites we classify as malware.”
Renee Burton, vice president of threat intel at the DNS security firm Infoblox, said many people erroneously assumed that the skewed Cloudflare domain rankings meant there were more bot-infected devices than there were regular devices querying sites like Google and Apple and Microsoft.
“Cloudflare’s documentation is clear — they know that when it comes to ranking domains you have to make choices on how to normalize things,” Burton wrote on LinkedIn. “There are many aspects that are simply out of your control. Why is it hard? Because reasons. TTL values, caching, prefetching, architecture, load balancing. Things that have shared control between the domain owner and everything in between.”
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