Cryptojacking Takes a New Turn in CryptoSink Campaign

Apparently there is no honor among thieves as a newly discovered attack dubbed "CryptoSink" reveals that attackers are shutting down rival cryptojacking efforts.


Researchers from F5 Labs reported on March 14 that they have discovered a new cryptojacking campaign that is abusing unpatched Elasticsearch servers.

Unauthorized cryptocurrency mining, commonly referred to as "cryptojacking," is an attack trend that started in 2017 and hit a peak in mid-2018. With a cryptojacking attack, a hacker makes use of a system or server resources to help mine cryptocurrency. F5 Labs is dubbing the cryptojacking campaign it discovered "CryptoSink" as the attackers are identifying systems that have already been compromised by cryptojacking and are "sinkholing" or redirecting the competitive mining effort. When the competitive cryptojacking effort is sinkholed, it is effectively shut down in favor of the new CryptoSink effort.

In the CryptoSink campaign, F5 Labs discovered that attackers are making use of a vulnerability in the open-source ElasticSearch application that is widely deployed on Linux servers. The ElasticSearch vulnerability is a 5-year-old issue identified by F5 Labs as CVE-2014-3120, which can enable an attacker to execute arbitrary code.

Maxim Zavodchik, security research group manager at F5 Networks, told eWEEK that his team discovered the attack via its honeynet network. A honeynet is made up of a series of honeypots, which are purposefully insecure instances that are designed to attract attackers. Zavodchik noted that attackers taking aim at older unpatched vulnerabilities to deploy cryptocurrency mining software and other forms of malware is not a new phenomenon.

"There are many threat actors still targeting old vulnerabilities, like Apache Struts2 Jakarta Multipart Parser (CVE-2017-5638) that was used to breach Equifax," Zavodchik said.

How CryptoSink Works

There are multiple methods that attackers can use to get a cryptocurrency miner on a system. In the CryptoSink campaign, F5 Labs found that the attackers were deploying software to mine the Monero (XMR) cryptocurrency. The XMR miner is deployed on either Linux or Windows servers and is able to consume system resources, making an infected server appear to run slower for regular operations.

As part of CryptoSink, the attackers use a dropper to "drop" or install a file that leads to the XMR miner installation. According to F5 Labs, at the time the research group discovered the attack, most antivirus (AV) technologies did not actually detect the dropper file as being malware. Zavodchik commented that he wasn't surprised that the CryptoSink dropper wasn't detected, as the antivirus solutions for Linux servers still don’t seem to be as focused on endpoints as the solutions are for Windows servers. 

"Many times we see Linux malware going undetected or strongly misclassified," Zavodchik said. "We might also speculate that as the malware was trying to keep it simple, without sophisticated packing or process injections, it was ironically going under the radar of the AVs." 

If the CryptoSink campaign detected that a given server was already running a cryptocurrency mining software application, the attackers ended up redirecting that traffic to a sinkhole, effectively shutting down the competitive mining activity.


Cryptojacking efforts overall have had declining impact in recent months as the value of the Monero cryptocurrency has declined precipitously. One Monero as of March 14 is worth approximately $47, which is down from its one-year high of approximately $300.

For the CryptoSink campaign, Zavodchik said that F5 Labs has identified at least two cryptocurrency wallets where the mining proceeds were directed. He said that looking at just the two wallets, approximately $4,500 was mined in two weeks. That said, he noted there could be many more wallets because there could be many more malware instances that didn’t get to the F5 Labs honeynet.

What Organization Should Do to Reduce the Risk

The most obvious thing that every organization can and should do to minimize the risk of being a victim of CryptoSink or other cryptojacking efforts is to keep system and application software fully patched and updated.

Additionally, Zavodchik recommends that organizations use antivirus technology that is specialized for Linux servers to help catch potential malware. He also suggests the use of a Web Application Firewall (WAF) to help prevent potential infections as well. Finally, Zavodchik emphasized that organizations should make sure that database and remote access tools like SSH are protected with strong passwords.

Sean Michael Kerner is a senior editor at eWEEK and Follow him on Twitter @TechJournalist.

Sean Michael Kerner

Sean Michael Kerner

Sean Michael Kerner is an Internet consultant, strategist, and contributor to several leading IT business web sites.