A recently discovered Linux crypto-miner botnet spreading over the SSH protocol is based on the Python scripting language, which makes it difficult to detect, F5 Networks has discovered.
Dubbed PyCryptoMiner, the botnet is using Pastebin to receive new command and control server (C&C) assignments when the original C&C isn’t available. Under active development, the botnet recently added scanner functionality hunting for vulnerable JBoss servers (exploiting CVE-2017-12149), F5 says.
Designed to mine for Monero, a highly anonymous crypto-currency, the botnet is estimated to have generated the equivalent of approximately $46,000 as of late December.
PyCryptoMiner isn’t the only botnet targeting online Linux systems, but because of its scripting language-based nature, the malware is more evasive and be easily obfuscated. Furthermore, it is executed by a legitimate binary, F5's researchers discovered.
The botnet spreads by attempting to guess the SSH login credentials of target Linux machines. If the credentials are successfully discovered, the attacking bot deploys a simple base64-encoded spearhead Python script designed to connect to the C&C server to download and execute additional Python code.
The second-stage code is the main bot controller, which registers a cron job on the infected machine to create persistency.
The original spearhead bash script also collects information on the infected device, including Host/DNS name, OS name and architecture, number of CPUs, and CPU usage. It also checks whether the machine has been already infected and whether the bot is used for crypto-mining or scanning.
The bot then sends a report with the collected information to the C&C, which responds with task details. Tasks include arbitrary commands to be executed, update, identifier so the C&C can synchronize botnet results, and time interval to poll the C&C. The bot sends an output of the executed task to the C&C.
In mid-December, the botnet was updated with code to scan for vulnerable JBoss servers, in an attempt to exploit CVE-2017-12149, a vulnerability disclosed several months ago.
“The list of the targets to scan is controlled by the C&C server, while the bot has a separate thread that polls the C&C server for new targets. The server responds with a Class C IP range to scan but could also provide a single IP address,” the researchers reveal.
The botnet uses two pool addresses that show approximately 94 and 64 Monero, with a value of around $60,000. However, the researchers are uncertain how much profit the threat actor behind the malware has made overall.
Unlike other malware that has the C&C server address hardcoded, which causes bots to become unreachable when the server is taken down, the botnet uses Pastebin to publish an alternate C&C server address if the original one is unreachable.
According to F5, with all C&C servers of the botnet inaccessible at this moment, all newly infected bots are idle, polling for the attacker’s Pastebin.com page, which could be updated at any time.
The page allowed researchers to determine that the botnet might have been active since August 2017, and that the resource had been viewed 177,987 times at the time of the investigation. However, the researchers couldn’t determine the exact size of the botnet, as a single bot could periodically ask the resource if the C&C server is down.
Looking at other resources created by the same actor, who uses the moniker “WHATHAPPEN”, the researchers discovered 235 email addresses and more than 36,000 domains associated with them. The registrant has been involved in scams, gambling, and adult services since 2012.
“Our research is still ongoing while we hunt for more missing pieces of this puzzle, such as the “scanner node” component and additional C&C servers, if there are any. We are also waiting to see whether the current C&C server will come back to life,” F5 notes.
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