A worm observed in thousands of attacks this year features sophisticated protection mechanisms that allow it to remain on infected systems for years, GuardiCore security researchers warn.
Dubbed PhotoMiner, the worm spreads through infecting websites that are hosted on FTP servers, and brings its authors money by mining for the Monero crypto-currency. According to researchers, the worm has a unique multi-stage infection mechanism, has a modular design, and registers itself as a startup program to achieve persistence.
The infection chain starts with insecure FTP servers being attacked and websites hosted alongside them being compromised to infect their visitors with the malware. Once present on the end-user machine, the worm not only starts mining for crypto-currency, but also attempts to infect additional FTP servers and systems in local networks.
Attackers are brute forcing random IP addresses and, by working off a user/password dictionary, they manage to compromise poorly protected FTP servers. Next, they upload a copy of the malware to each writeable server, and each file that helps infecting the user is injected with a specific string of code. The worm is served to end users in the form of a download that pops up in vulnerable browsers, researchers say.
PhotoMiner also leverages built-in Windows systems tools to scan the local network segment, after which is attempts to brute force a connection over the Server Message Block (SMB) Protocol. When successful, it attempts to drop copies of itself into every accessible remote startup location and uses Windows Management Instrumentation (WMI) scripting to execute local copies.
First observed in December last year, when it included the core miner and basic propagation abilities, the worm has already seen a series of updates, and researchers have already identified two different variants over a dozen versions of the malware to date. However, all versions follow the same order of operations, starting with achieving persistence and collecting configuration data for the miner.
For persistence, the malware registers as a startup program, after which it connects via HTTP to a list of predefined hostnames to acquire the configuration data. At the moment, the configuration file, which is scrambled using a basic reverse-dictionary, includes a list of Monero pools and wallets, and the malware picks a random one from there. The worm also connects to the command and control (C&C) server to send system information and to report on its progress.
GuardiCore researchers also say that the attackers have built a resilient backend that is spread over multiple domain names and that they are using virtual private servers across different hosting providers. However, they are reusing servers and IP addresses, which allowed researchers to tie together different campaigns.
The researchers also say that, after initialization, the malware “spins off” the miner as a separate process, while it continues to focus on spreading itself. Courtesy of this approach, the malware ensures that the miner is safe from antivirus programs even if the worm is detected and countered. The mining module is a packed version of BitMonero, the core implementation of the Monero worker, thus a legitimate program that might not attract a lot of attention.
Non-secure services facing the Internet, such as unprotected FTP servers, represent one of the most common ways of infiltrating an organization. “Infecting websites through unprotected FTP servers is a classic attack that seems to be gaining popularity once again. By creating an infection that is hard to disrupt, the writers of PhotoMiner have created a botnet that is undoubtedly here to stay,” GuardiCore researchers conclude.