He cited the company's telemetry that showed the popularity of the exploit, one of many crafted by the NSA and leaked on the Web in April 2016 by a group known as the Shadow Brokers, had been growing over the last few months, with a recent spike being even bigger that its peaks in 2017.
EternalBlue exploits a flaw in an obsolete version of Microsoft's implementation of the Server Message Block protocol through port 445; it was patched by the company a month before the exploit was leaked. To this day, there is no clue as to the identity of the Shadow Brokers.
If the attacker found a vulnerable system, then a payload of his/her choice would be run on the target and this was how WannaCry was distributed across networks.
WannaCry was stopped in its tracks when British security researcher Marcus Hutchins registered a domain he had found in its source code; the malware had been programmed to check this domain, and continue spreading if it could not access the domain.
Kubovič said EternalBlue had a quiet period after the ravages of WannaCry, with detections dropping to a few hundred a day. But since September 2017, the use of the exploit had continued to grow and had reached new heights in mid-April.
"One possible explanation for the latest peak is the Satan ransomware campaign seen around those dates, but it could be connected to other malicious activities as well," he said.
Apart from WannaCry, EternalBlue has also powered the Petya (aka NotPetya, Nyetya or Golden Eye) ransomware in June 2017 and the BadRabbit ransomware campaign in the last three months of 2017. It was also used by the Sednit (aka APT28, Fancy Bear and Sofacy) cyber-espionage group to attack Wi-Fi networks in European hotels.
"This exploit and all the attacks it has enabled so far highlight the importance of timely patching as well as the need for a reliable and multi-layered security solution that can block the underlying malicious tool," Kubovič said.