A cyberattack that crippled Internet services for nearly one million customers of Deutsche Telekom earlier this week suggests that the threat posed by the Mirai IoT botnet malware is about to get a lot larger.
The attack is the first since Mirai surfaced in October that does not rely on weak and default passwords in routers, webcams, digital video recorders, and other so-called Internet of Things devices.
Instead it targeted a specific vulnerability in a management interface present in routers used by many customers of Deutsche Telekom with the goal of infecting the devices and making them part of a Mirai botnet. The infection attempts failed but nevertheless caused the routers to crash.
“Until now, Mirai just used weak passwords to exploit devices like routers. But with this version, it adds an exploit for a vulnerability in a web service,” says Johannes Ullrich, dean of research at the SANS Institute.
The kind of vulnerability that was exploited in the attack is very common, he says. “What we see right now is more or less just a tip of the iceberg. By adding this exploit, Mirai gained access to many more devices then it already had,” he said.
The disruptions for Deutsche Telekom customers started Sunday and continued through parts of early Monday. In all, about 900,000 customers, representing about 4% of the company’s 20 million fixed-line customers, were impacted in the attack, Deutsche Telekom said in a FAQ and alert on the incident.
By early Monday, the company had begun rolling out patches for the problem to affected customers. It advised customers to unplug their router for 30 seconds and then power the device back on for the update to take hold. It also offered a location where users could go to download the update manually and install it on their routers.
The fact that threat actors are attempting to distribute Mirai by exploiting software vulnerabilities in IoT devices is troubling, says Craig Young, security researcher at Tripwire.
“The most defining attribute is that this Mirai variant is propagating through a specific vulnerability rather than relying on poorly configured devices,” Young says. “The last wave of attacks would seek out devices with exposed Telnet or SSH management and attempt to guess passwords.”
Device owners could easily thwart such attacks by using a strong password or not directly exposing the management service to the Internet, Young says.
In contrast “this attack could not be blocked through any configuration change made by the end user,” Young says. “The management protocol being attacked is exposed in the device configuration required by various ISPs and is not one that consumers could disable,” on their own without a vendor-supplied patch, Young says.
In a SANS Internet Storm Center advisory, Ullrich identified the Deutsche Telekom routers that were attacked as originating from Acadyn, a Taiwanese modem manufacturer. But the vulnerable interface is present in other routers as well, including those from Zyxel, a maker of modems used by Irish ISP Eir, Ullrich said in the alert.
A count performed using the Shodan Internet scanning tool shows the total number of devices listening in on the port used by the management interface is as large as 40 million. But not all of them are likely to run the vulnerable implementations that were present in the Deutsche Telekom routers. “My personal "best guess" is that this vulnerability may have added 1-2 Million new bots to the Mirai botnet,” Ullrich wrote in the alert.
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