Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Threat Intelligence

9/18/2019
11:40 AM
50%
50%

Cryptominer Attacks Ramp Up, Focus on Persistence

The latest attacks, such as Skidmap and Smominru, add capabilities to allow them to persist longer on Windows and Linux systems, surviving initial attempts at eliminating them.

In 2018, opportunistic cybercriminals had an easy way to monetize compromised web servers: Add JavaScript from the cryptomining-as-a-service provider Coinhive to eke out small profits for every compromised server by surreptitiously having them do the cryptography tasks necessary to generate Monero cryptocurrency.

With Coinhive's shutdown in March 2019, however, cybercriminals have resorted to more standard tactics, infecting Windows and Linux servers and finding ways to allow their malware to persist for longer periods. 

Two research analyses released this week by Trend Micro and Guardicore highlight the techniques used by cybercriminals' attempts to maintain their control of compromised servers. In a September 16 report, security firm Trend Micro found that the Skidmap Linux malware uses a variety of techniques — from the complex, such as loading malicious kernel modules, to the simple, such as inserting SSH keys into the authorized-keys file. Meanwhile, the 2-year-old Smominru botnet has used a variety of techniques to hold its ground on the more than 4,900 networks and 90,000 servers a month the malware infects every month.

On compromised Windows servers, Smominru schedules tasks using scripts, exploits the SQL service, creates administrative users, and installs a remote access trojan, says Ophir Harpaz, a security researcher at Guardicore Labs.

"They are just shooting in as many directions as possible," she says, adding that the attackers are not just worried about defenders. "These threat actors are trying to eliminate each other, so the more ways you find to be persistence on the machine, the less chance you have of losing access to the compromised host."

While cryptomining peaked in 2018, when 42% of companies saw attacks, the attack technique is still a major threat, according to data from networking security firm Check Point Software Technologies. In the first half of 2019, the company found 21% of networks had one or more machines infected with cryptomining malware. That decline is due to the shutdown of the Coinhive mining service, which allowed attackers to inject unwanted — and many would say, malicious — JavaScript into websites to force browsers to process the resource-intensive computations required to "mine" for the Monero cryptocurrency. The service claimed to be making $250,000 a month while controlling 62% of the cryptojacking market

Because such easy-to-use services are no longer the rule, adding persistence to cryptomining malware has become a priority for cybercriminals, Augusto Remillano II and Jakub Urbanec, threat analysts at Trend Micro, stated in their analysis of Skidmap. The researchers found that the attackers, like the Smominru group, have taken a kitchen-sink approach, using techniques from Linux kernel module (LKM) rootkits to overwriting the rm binary for the Linux command used to remove software.

"Its use of LKM rootkits — given their capability to overwrite or modify parts of the kernel — makes it harder to clean compared to other malware," the researchers stated in the analysis. "In addition, Skidmap has multiple ways to access affected machines, which allow it to reinfect systems that have been restored or cleaned up."

In its research into Smominru, Guardicore's team found the credentials for a command-and-control server that collected information on the botnet, finding information and credentials for compromised servers. The security firm monitored the information on the server over time to study the infection patterns. About a quarter of the systems had been infected more than once, showing that the focus on persistence pays off for the attackers.

And the focus becomes more important because the vast majority of computers on the Internet are difficult to infect. For every organization serious about security, there are a few individuals or small businesses that have a few machines that have not been updated or secured, says Daniel Goldberg, a security researcher with Guardicore. 

"Many groups compete to be on the same small number of machines — it's still hundreds of thousands of machines, but only a fraction on what is on the Internet," he says. "There is this whole undergrowth of forgotten servers lying around on the Internet and available for hacking."

The company estimates that the botnet has control of an average of 6,500 processing cores per day to use for cryptomining.

Therefore, any attempt at persistence can pay off for attackers. The Linux cryptominer Skidmap, for example, even adds an SSH key to the authorized keys file on Linux, allowing for a simple but effective form of a backdoor. This often works because companies do not monitor those files, Kevin Bocek, vice president of security strategy and threat intelligence at security firm Venafi, said in a statement. 

"We see these tactics used so effectively to target critical infrastructure because security teams rarely have oversight of SSH keys that control access," he said. "These keys don't expire — creating an encrypted backdoor that attackers can use until they're detected."

While the recent attack focus on both Windows and Linux, some experts see Linux servers to be an increasingly valuable target for attackers focused on cryptomining. 

"Over the last several months, we've seen more evidence that suggests that attackers are continuing to increase their focus on Linux as a vehicle to obtain access to compute and bandwidth resources," Casey Ellis, chief technology officer and founder of crowdsourced security firm Bugcrowd, said in a statement. 

For server administrators, the best defense is to keep your servers updated and patched and monitor their performance. If the company often uses open source repositories, they should be verified. And all systems should enforce the concepts of least privilege, only allowing the level of access necessary to the user.

While cryptomining is often not considered as significant a threat as, say, ransomware, allowing attackers to steal processing power can have a significant impact on a company, Trend Micro's researchers said.

"Cryptocurrency-mining threats don't just affect a server or workstation's performance — they could also translate to higher expenses and even disrupt businesses especially if they are used to run mission-critical operations," they stated in their analysis. "Given Linux's use in many enterprise environments, its users, particularly administrators, should always adopt best practices."

Related Content:

Check out The Edge, Dark Reading's new section for features, threat data, and in-depth perspectives. Today's top story: "Poll Results: Maybe Not Burned Out, But Definitely 'Well Done'

Veteran technology journalist of more than 20 years. Former research engineer. Written for more than two dozen publications, including CNET News.com, Dark Reading, MIT's Technology Review, Popular Science, and Wired News. Five awards for journalism, including Best Deadline ... View Full Bio

Comment  | 
Print  | 
More Insights
Comments
Oldest First  |  Newest First  |  Threaded View
Mobile Banking Malware Up 50% in First Half of 2019
Kelly Sheridan, Staff Editor, Dark Reading,  1/17/2020
Exploits Released for As-Yet Unpatched Critical Citrix Flaw
Jai Vijayan, Contributing Writer,  1/13/2020
Microsoft to Officially End Support for Windows 7, Server 2008
Kelly Sheridan, Staff Editor, Dark Reading,  1/13/2020
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Write a Caption, Win a Starbucks Card! Click Here
Latest Comment: This comment is waiting for review by our moderators.
Current Issue
The Year in Security: 2019
This Tech Digest provides a wrap up and overview of the year's top cybersecurity news stories. It was a year of new twists on old threats, with fears of another WannaCry-type worm and of a possible botnet army of Wi-Fi routers. But 2019 also underscored the risk of firmware and trusted security tools harboring dangerous holes that cybercriminals and nation-state hackers could readily abuse. Read more.
Flash Poll
[Just Released] How Enterprises are Attacking the Cybersecurity Problem
[Just Released] How Enterprises are Attacking the Cybersecurity Problem
Organizations have invested in a sweeping array of security technologies to address challenges associated with the growing number of cybersecurity attacks. However, the complexity involved in managing these technologies is emerging as a major problem. Read this report to find out what your peers biggest security challenges are and the technologies they are using to address them.
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2020-7227
PUBLISHED: 2020-01-18
Westermo MRD-315 1.7.3 and 1.7.4 devices have an information disclosure vulnerability that allows an authenticated remote attacker to retrieve the source code of different functions of the web application via requests that lack certain mandatory parameters. This affects ifaces-diag.asp, system.asp, ...
CVE-2019-15625
PUBLISHED: 2020-01-18
A memory usage vulnerability exists in Trend Micro Password Manager 3.8 that could allow an attacker with access and permissions to the victim's memory processes to extract sensitive information.
CVE-2019-19696
PUBLISHED: 2020-01-18
A RootCA vulnerability found in Trend Micro Password Manager for Windows and macOS exists where the localhost.key of RootCA.crt might be improperly accessed by an unauthorized party and could be used to create malicious self-signed SSL certificates, allowing an attacker to misdirect a user to phishi...
CVE-2019-19697
PUBLISHED: 2020-01-18
An arbitrary code execution vulnerability exists in the Trend Micro Security 2019 (v15) consumer family of products which could allow an attacker to gain elevated privileges and tamper with protected services by disabling or otherwise preventing them to start. An attacker must already have administr...
CVE-2019-20357
PUBLISHED: 2020-01-18
A Persistent Arbitrary Code Execution vulnerability exists in the Trend Micro Security 2020 (v160 and 2019 (v15) consumer familiy of products which could potentially allow an attacker the ability to create a malicious program to escalate privileges and attain persistence on a vulnerable system.