A recently patched Samba flaw known as EternalRed and SambaCry has been exploited in the wild to deliver a cryptocurrency miner to vulnerable machines, researchers warned.
These attacks, observed by both Kaspersky and Cyphort, were launched shortly after the existence of the security hole was brought to light and proof-of-concept (PoC) exploits were made available.
The vulnerability, tracked as CVE-2017-7494, affects all versions of Samba since 3.5.0 and it has been addressed with the release of versions 4.6.4, 4.5.10 and 4.4.14. The flaw allows a malicious client to upload a shared library to a writable share, and cause the server to execute the file.
In the attacks spotted by researchers, cybercriminals attempted to deliver files with a random name and a .so extension (e.g. GJZjrflB.so, INAebsGB.so, cblRWuoCc.so).
The attackers first identified writable shares to which they could deliver their payload. In earlier attacks, the cybercriminals attempted to guess the local path needed to exploit the vulnerability, but Cyphort noticed that they later turned to using the NetShareGetInfo method, which provides information about a particular shared resource on a server.
The first file delivered is a backdoor that provides the attackers a reverse shell they can leverage to remotely execute commands. Experts pointed out that this part of the attack is based on the Metasploit module released shortly after CVE-2017-7494 was disclosed.
The backdoor is used to download and execute a popular open-source cryptocurrency miner named cpuminer (miderd). The miner is configured to abuse compromised systems to mine Monero (XMR) and send it to a wallet whose address is hardcoded.
Kaspersky analyzed the wallet and found that, as of June 8, the attackers had obtained nearly 100 Monero, which is currently worth roughly $5,500. The domain from which the mining utility is downloaded was registered on April 29 and the attackers’ wallet started receiving Monero the next day.
During the first two weeks the wallet received only one Monero per day, but the amount increased following the disclosure of CVE-2017-7494, and recently the attackers have been earning roughly 5 Monero each day.
“The attacked machine turns into a workhorse on a large farm, mining crypto-currency for the attackers,” Kaspersky researchers said in a blog post. “In addition, through the reverse-shell left in the system, the attackers can change the configuration of a miner already running or infect the victim’s computer with other types of malware.”
The Samba vulnerability has been found to affect many networking devices, including Cisco, Netgear, QNAP, Synology, Varitas and NetApp products.