A recently discovered variant of the Mirai Internet of Things (IoT) malware is using a command and control (C&C) server on the Tor network, Trend Micro’s security researchers have discovered.
Ever since Mirai’s source code was posted online in October 2016, miscreants have released variants of the malware to expand its targeting capabilities and ensnare as many devices as possible in distributed denial of service (DDoS)-capable botnets.
Some of the best known Mirai spawns include Echobot, Wicked, Satori, Okiru, Masuta, and Miori, but others have been observed over the years as well, including a variant that specifically targets business devices. Recently, a Mirai-based botnet was used in a massive 292,000 RPS Layer 7 assault.
The newly discovered Mirai sample, Trend Micro points out, is proof that cybercriminals continue to develop and use the malware’s code despite the massive attention it has received over the years.
Just as other Mirai iterations out there, the new variant allows attackers to remotely access and control IoT devices such as IP cameras and DVRs, using exposed ports and default credentials. The infected devices can be then leveraged for DDoS assaults using various methods.
What sets the new version apart, however, is the fact that its author has placed the botnet’s command and control (C&C) server on the Tor anonymity network, in an attempt to prevent security researchers from taking it down.
The new sample also has a total of 30 hard-coded IP addresses and uses a socks5 protocol initial handshake message, with all of the hard-coded servers being socks proxies to the Tor network.
The malware would select a random server as proxy, would then start the connection with socks5, and then query it to relay packets to a C&C server with the address nd3rwzslqhxibkl7[.]onion:1356. If the relay connection fails, the malware attempts the process with another proxy server.
“Connecting to the C&C with a Tor proxy in a testing environment, we confirmed this as it returned a login prompt for the attacker, exactly the same prompt as other C&C servers have returned with previous Mirai variants,” Trend Micro reveals.
The configuration values in this sample were encrypted by XOR with 0x22 (34) and embedded in its binary, a feature observed in other Mirai variants as well. A string “LONGNOSE: applet not found” discovered in the sample could be used to identify it.
The malware was observed scanning for random IP addresses with TCP ports 9527 and 34567, likely specific to exposed IP cameras and DVRs for remote access and control, Trend Micro says. Possible default credentials for login attempts are located in the threat’s configuration.
“We find this particular sample interesting for the attackers’ decision to place the C&C server in Tor, likely to evade tracking of its IP address and avoiding being shut down when reported to domain hosts. […]While there have been previous reports of other malware having their C&C hidden in Tor, we see this as a possible precedent for other evolving IoT malware families,” Trend Micro concludes.
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