Introduction

Cyber criminals tend to favor cryptocurrencies because they provide a certain level of anonymity and can be easily monetized. This interest has increased in recent years, stemming far beyond the desire to simply use cryptocurrencies as a method of payment for illicit tools and services. Many actors have also attempted to capitalize on the growing popularity of cryptocurrencies, and subsequent rising price, by conducting various operations aimed at them. These operations include malicious cryptocurrency mining (also referred to as cryptojacking), the collection of cryptocurrency wallet credentials, extortion activity, and the targeting of cryptocurrency exchanges.

This blog post discusses the various trends that we have been observing related to cryptojacking activity, including cryptojacking modules being added to popular malware families, an increase in drive-by cryptomining attacks, the use of mobile apps containing cryptojacking code, cryptojacking as a threat to critical infrastructure, and observed distribution mechanisms.

What Is Mining?

As transactions occur on a blockchain, those transactions must be validated and propagated across the network. As computers connected to the blockchain network (aka nodes) validate and propagate the transactions across the network, the miners include those transactions into "blocks" so that they can be added onto the chain. Each block is cryptographically hashed, and must include the hash of the previous block, thus forming the "chain" in blockchain. In order for miners to compute the complex hashing of each valid block, they must use a machine's computational resources. The more blocks that are mined, the more resource-intensive solving the hash becomes. To overcome this, and accelerate the mining process, many miners will join collections of computers called "pools" that work together to calculate the block hashes. The more computational resources a pool harnesses, the greater the pool's chance of mining a new block. When a new block is mined, the pool's participants are rewarded with coins. Figure 1 illustrates the roles miners play in the blockchain network.

Figure 1: The role of miners

Underground Interest

FireEye iSIGHT Intelligence has identified eCrime actor interest in cryptocurrency mining-related topics dating back to at least 2009 within underground communities. Keywords that yielded significant volumes include miner, cryptonight, stratum, xmrig, and cpuminer. While searches for certain keywords fail to provide context, the frequency of these cryptocurrency mining-related keywords shows a sharp increase in conversations beginning in 2017 (Figure 2). It is probable that at least a subset of actors prefer cryptojacking over other types of financially motivated operations due to the perception that it does not attract as much attention from law enforcement.

Figure 2: Underground keyword mentions

Monero Is King

The majority of recent cryptojacking operations have overwhelmingly focused on mining Monero, an open-source cryptocurrency based on the CryptoNote protocol, as a fork of Bytecoin. Unlike many cryptocurrencies, Monero uses a unique technology called "ring signatures," which shuffles users' public keys to eliminate the possibility of identifying a particular user, ensuring it is untraceable. Monero also employs a protocol that generates multiple, unique single-use addresses that can only be associated with the payment recipient and are unfeasible to be revealed through blockchain analysis, ensuring that Monero transactions are unable to be linked while also being cryptographically secure.

The Monero blockchain also uses what's called a "memory-hard" hashing algorithm called CryptoNight and, unlike Bitcoin's SHA-256 algorithm, it deters application-specific integrated circuit (ASIC) chip mining. This feature is critical to the Monero developers and allows for CPU mining to remain feasible and profitable. Due to these inherent privacy-focused features and CPU-mining profitability, Monero has become an attractive option for cyber criminals.

Underground Advertisements for Miners

Because most miner utilities are small, open-sourced tools, many criminals rely on crypters. Crypters are tools that employ encryption, obfuscation, and code manipulation techniques to keep their tools and malware fully undetectable (FUD). Table 1 highlights some of the most commonly repurposed Monero miner utilities.

Table 1: Commonly used Monero miner utilities

The following are sample advertisements for miner utilities commonly observed in underground forums and markets. Advertisements typically range from stand-alone miner utilities to those bundled with other functions, such as credential harvesters, remote administration tool (RAT) behavior, USB spreaders, and distributed denial-of-service (DDoS) capabilities.

Sample Advertisement #1 (Smart Miner + Builder)

In early April 2018, actor "Mon£y" was observed by FireEye iSIGHT Intelligence selling a Monero miner for $80 USD – payable via Bitcoin, Bitcoin Cash, Ether, Litecoin, or Monero – that included unlimited builds, free automatic updates, and 24/7 support. The tool, dubbed Monero Madness (Figure 3), featured a setting called Madness Mode that configures the miner to only run when the infected machine is idle for at least 60 seconds. This allows the miner to work at its full potential without running the risk of being identified by the user. According to the actor, Monero Madness also provides the following features:

• Unlimited builds
• Builder GUI (Figure 4)
• Written in AutoIT (no dependencies)
• FUD
• Safer error handling
• Uses most recent XMRig code
• Customizable pool/port
• Packed with UPX
• Works on all Windows OS (32- and 64-bit)
• Madness Mode option

Figure 3: Monero Madness

Figure 4: Monero Madness builder

Sample Advertisement #2 (Miner + Telegram Bot Builder)

In March 2018, FireEye iSIGHT Intelligence observed actor "kent9876" advertising a Monero cryptocurrency miner called Goldig Miner (Figure 5). The actor requested payment of $23 USD for either CPU or GPU build or $50 USD for both. Payments could be made with Bitcoin, Ether, Litecoin, Dash, or PayPal. The miner ostensibly offers the following features:

• Written in C/C++
• Build size is small (about 100–150 kB)
• Hides miner process from popular task managers
• Can run without Administrator privileges (user-mode)
• Auto-update ability
• All data encoded with 256-bit key
• Access to Telegram bot-builder
• Lifetime support (24/7) via Telegram

Figure 5: Goldig Miner advertisement

Sample Advertisement #3 (Miner + Credential Stealer)

In March 2018, FireEye iSIGHT Intelligence observed actor "TH3FR3D" offering a tool dubbed Felix (Figure 6) that combines a cryptocurrency miner and credential stealer. The actor requested payment of $50 USD payable via Bitcoin or Ether. According to the advertisement, the Felix tool boasted the following features:

• Written in C# (Version 1.0.1.0)
• Browser stealer for all major browsers (cookies, saved passwords, auto-fill)
• Monero miner (uses minergate.com pool by default, but can be configured)
• Filezilla stealer
• Desktop file grabber (.txt and more)
• Can download and execute files
• Update ability
• USB spreader functionality
• PHP web panel

Figure 6: Felix HTTP

Sample Advertisement #4 (Miner + RAT)

In January 2018, FireEye iSIGHT Intelligence observed actor "ups" selling a miner for any Cryptonight-based cryptocurrency (e.g., Monero and Dashcoin) for either Linux or Windows operating systems. In addition to being a miner, the tool allegedly provides local privilege escalation through the CVE-2016-0099 exploit, can download and execute remote files, and receive commands. Buyers could purchase the Windows or Linux tool for €200 EUR, or €325 EUR for both the Linux and Windows builds, payable via Monero, bitcoin, ether, or dash. According to the actor, the tool offered the following:

Windows Build Specifics

• Written in C++ (no dependencies)
• Miner component based on XMRig
• Easy cryptor and VPS hosting options
• Web panel (Figure 7)
• Uses TLS for secured communication
• Download and execute
• Auto-update ability
• Cleanup routine
• Receive remote commands
• Perform privilege escalation
• Features "game mode" (mining stops if user plays game)
• Proxy feature (based on XMRig)
• Support (for €20/month)
• Kills other miners from list
• Hidden from TaskManager
• Configurable pool, coin, and wallet (via panel)
• Can mine the following Cryptonight-based coins:
  • Monero
  • Bytecoin
  • Electroneum
  • DigitalNote
  • Karbowanec
  • Sumokoin
  • Fantomcoin
  • Dinastycoin
  • Dashcoin
  • LeviarCoin
  • BipCoin
  • QuazarCoin
  • Bitcedi

Linux Build Specifics

• Issues running on Linux servers (higher performance on desktop OS)
• Compatible with AMD64 processors on Ubuntu, Debian, Mint (support for CentOS later)

Figure 7: Miner bot web panel

Sample Advertisement #5 (Miner + USB Spreader + DDoS Tool)

In August 2017, actor "MeatyBanana" was observed by FireEye iSIGHT Intelligence selling a Monero miner utility that included the ability to download and execute files and perform DDoS attacks. The actor offered the software for $30 USD, payable via Bitcoin. Ostensibly, the tool works with CPUs only and offers the following features:

• Configurable miner pool and port (default to minergate)
• Compatible with both 64- and 86-bit Windows OS
• Hides from the following popular task managers:
• Windows Task Manager
• Process Killer
• KillProcess
• System Explorer
• Process Explorer
• AnVir
• Process Hacker
• Masked as a system driver
• Does not require administrator privileges
• No dependencies
• Registry persistence mechanism
• Ability to perform "tasks" (download and execute files, navigate to a site, and perform DDoS)
• USB spreader
• Support after purchase

The Cost of Cryptojacking

The presence of mining software on a network can generate costs on three fronts as the miner surreptitiously allocates resources:

1. Degradation in system performance
2. Increased cost in electricity
3. Potential exposure of security holes

Cryptojacking targets computer processing power, which can lead to high CPU load and degraded performance. In extreme cases, CPU overload may even cause the operating system to crash. Infected machines may also attempt to infect neighboring machines and therefore generate large amounts of traffic that can overload victims' computer networks.

In the case of operational technology (OT) networks, the consequences could be severe. Supervisory control and data acquisition/industrial control systems (SCADA/ICS) environments predominately rely on decades-old hardware and low-bandwidth networks, therefore even a slight increase in CPU load or the network could leave industrial infrastructures unresponsive, impeding operators from interacting with the controlled process in real-time.

The electricity cost, measured in kilowatt hour (kWh), is dependent upon several factors: how often the malicious miner software is configured to run, how many threads it's configured to use while running, and the number of machines mining on the victim's network. The cost per kWh is also highly variable and depends on geolocation. For example, security researchers who ran Coinhive on a machine for 24 hours found that the electrical consumption was 1.212kWh. They estimated that this equated to electrical costs per month of $10.50 USD in the United States, $5.45 USD in Singapore, and $12.30 USD in Germany.

Cryptojacking can also highlight often overlooked security holes in a company's network. Organizations infected with cryptomining malware are also likely vulnerable to more severe exploits and attacks, ranging from ransomware to ICS-specific malware such as TRITON.

Cryptocurrency Miner Distribution Techniques

In order to maximize profits, cyber criminals widely disseminate their miners using various techniques such as incorporating cryptojacking modules into existing botnets, drive-by cryptomining attacks, the use of mobile apps containing cryptojacking code, and distributing cryptojacking utilities via spam and self-propagating utilities. Threat actors can use cryptojacking to affect numerous devices and secretly siphon their computing power. Some of the most commonly observed devices targeted by these cryptojacking schemes are:

• User endpoint machines
• Enterprise servers
• Websites
• Mobile devices
• Industrial control systems

Cryptojacking in the Cloud

Private sector companies and governments alike are increasingly moving their data and applications to the cloud, and cyber threat groups have been moving with them. Recently, there have been various reports of actors conducting cryptocurrency mining operations specifically targeting cloud infrastructure. Cloud infrastructure is increasingly a target for cryptojacking operations because it offers actors an attack surface with large amounts of processing power in an environment where CPU usage and electricity costs are already expected to be high, thus allowing their operations to potentially go unnoticed. We assess with high confidence that threat actors will continue to target enterprise cloud networks in efforts to harness their collective computational resources for the foreseeable future.

The following are some real-world examples of cryptojacking in the cloud:

• In February 2018, FireEye researchers published a blog detailing various techniques actors used in order to deliver malicious miner payloads (specifically to vulnerable Oracle servers) by abusing CVE-2017-10271. Refer to our blog post for more detailed information regarding the post-exploitation and pre-mining dissemination techniques used in those campaigns.
• In March 2018, Bleeping Computer reported on the trend of cryptocurrency mining campaigns moving to the cloud via vulnerable Docker and Kubernetes applications, which are two software tools used by developers to help scale a company's cloud infrastructure. In most cases, successful attacks occur due to misconfigured applications and/or weak security controls and passwords.
• In February 2018, Bleeping Computer also reported on hackers who breached Tesla's cloud servers to mine Monero. Attackers identified a Kubernetes console that was not password protected, allowing them to discover login credentials for the broader Tesla Amazon Web services (AWS) S3 cloud environment. Once the attackers gained access to the AWS environment via the harvested credentials, they effectively launched their cryptojacking operations.
• Reports of cryptojacking activity due to misconfigured AWS S3 cloud storage buckets have also been observed, as was the case in the LA Times online compromise in February 2018. The presence of vulnerable AWS S3 buckets allows anyone on the internet to access and change hosted content, including the ability to inject mining scripts or other malicious software.

Incorporation of Cryptojacking into Existing Botnets

FireEye iSIGHT Intelligence has observed multiple prominent botnets such as Dridex and Trickbot incorporate cryptocurrency mining into their existing operations. Many of these families are modular in nature and have the ability to download and execute remote files, thus allowing the operators to easily turn their infections into cryptojacking bots. While these operations have traditionally been aimed at credential theft (particularly of banking credentials), adding mining modules or downloading secondary mining payloads provides the operators another avenue to generate additional revenue with little effort. This is especially true in cases where the victims were deemed unprofitable or have already been exploited in the original scheme.

The following are some real-world examples of cryptojacking being incorporated into existing botnets:

• In early February 2018, FireEye iSIGHT Intelligence observed Dridex botnet ID 2040 download a Monero cryptocurrency miner based on the open-source XMRig miner.
• On Feb. 12, 2018, FireEye iSIGHT Intelligence observed the banking malware IcedID injecting Monero-mining JavaScript into webpages for specific, targeted URLs. The IcedID injects launched an anonymous miner using the mining code from Coinhive's AuthedMine.
• In late 2017, Bleeping Computer reported that security researchers with Radware observed the hacking group CodeFork leveraging the popular downloader Andromeda (aka Gamarue) to distribute a miner module to their existing botnets.
• In late 2017, FireEye researchers observed Trickbot operators deploy a new module named "testWormDLL" that is a statically compiled copy of the popular XMRig Monero miner.
• On Aug. 29, 2017, Security Week reported on a variant of the popular Neutrino banking Trojan, including a Monero miner module. According to their reporting, the new variant no longer aims at stealing bank card data, but instead is limited to downloading and executing modules from a remote server.

Drive-By Cryptojacking

In-Browser

FireEye iSIGHT Intelligence has examined various customer reports of browser-based cryptocurrency mining. Browser-based mining scripts have been observed on compromised websites, third-party advertising platforms, and have been legitimately placed on websites by publishers. While coin mining scripts can be embedded directly into a webpage's source code, they are frequently loaded from third-party websites. Identifying and detecting websites that have embedded coin mining code can be difficult since not all coin mining scripts are authorized by website publishers, such as in the case of a compromised website. Further, in cases where coin mining scripts were authorized by a website owner, they are not always clearly communicated to site visitors. At the time of reporting, the most popular script being deployed in the wild is Coinhive. Coinhive is an open-source JavaScript library that, when loaded on a vulnerable website, can mine Monero using the site visitor's CPU resources, unbeknownst to the user, as they browse the site.

The following are some real-world examples of Coinhive being deployed in the wild:

• In September 2017, Bleeping Computer reported that the authors of SafeBrowse, a Chrome extension with more than 140,000 users, had embedded the Coinhive script in the extension's code that allowed for the mining of Monero using users' computers and without getting their consent.
• During mid-September 2017, users on Reddit began complaining about increased CPU usage when they navigated to a popular torrent site, The Pirate Bay (TPB). The spike in CPU usage was a result of Coinhive's script being embedded within the site's footer. According to TPB operators, it was implemented as a test to generate passive revenue for the site (Figure 8).
• In December 2017, researchers with Sucuri reported on the presence of the Coinhive script being hosted on GitHub.io, which allows users to publish web pages directly from GitHub repositories.
• Other reporting disclosed the Coinhive script being embedded on the Showtime domain as well as on the LA Times website, both surreptitiously mining Monero.
• A majority of in-browser cryptojacking activity is transitory in nature and will last only as long as the user’s web browser is open. However, researchers with Malwarebytes Labs uncovered a technique that allows for continued mining activity even after the browser window is closed. The technique leverages a pop-under window surreptitiously hidden under the taskbar. As researchers pointed out, closing the browser window may not be enough to interrupt the activity, and that more advanced actions like running the Task Manager may be required.

Figure 8: Statement from TPB operators on Coinhive script

Malvertising and Exploit Kits

Malvertisements – malicious ads on legitimate websites – commonly redirect visitors of a site to an exploit kit landing page. These landing pages are designed to scan a system for vulnerabilities, exploit those vulnerabilities, and download and execute malicious code onto the system. Notably, the malicious advertisements can be placed on legitimate sites and visitors can become infected with little to no user interaction. This distribution tactic is commonly used by threat actors to widely distribute malware and has been employed in various cryptocurrency mining operations.

The following are some real-world examples of this activity:

• In early 2018, researchers with Trend Micro reported that a modified miner script was being disseminated across YouTube via Google's DoubleClick ad delivery platform. The script was configured to generate a random number variable between 1 and 100, and when the variable was above 10 it would launch the Coinhive script coinhive.min.js, which harnessed 80 percent of the CPU power to mine Monero. When the variable was below 10 it launched a modified Coinhive script that was also configured to harness 80 percent CPU power to mine Monero. This custom miner connected to the mining pool wss[:]//ws[.]l33tsite[.]info:8443, which was likely done to avoid Coinhive's fees.
• In April 2018, researchers with Trend Micro also discovered a JavaScript code based on Coinhive injected into an AOL ad platform. The miner used the following private mining pools: wss[:]//wsX[.]www.datasecu[.]download/proxy and wss[:]//www[.]jqcdn[.]download:8893/proxy. Examination of other sites compromised by this campaign showed that in at least some cases the operators were hosting malicious content on unsecured AWS S3 buckets.
• Since July 16, 2017, FireEye has observed the Neptune Exploit Kit redirect to ads for hiking clubs and MP3 converter domains. Payloads associated with the latter include Monero CPU miners that are surreptitiously installed on victims' computers.
• In January 2018, Check Point researchers discovered a malvertising campaign leading to the Rig Exploit Kit, which served the XMRig Monero miner utility to unsuspecting victims.

Mobile Cryptojacking

In addition to targeting enterprise servers and user machines, threat actors have also targeted mobile devices for cryptojacking operations. While this technique is less common, likely due to the limited processing power afforded by mobile devices, cryptojacking on mobile devices remains a threat as sustained power consumption can damage the device and dramatically shorten the battery life. Threat actors have been observed targeting mobile devices by hosting malicious cryptojacking apps on popular app stores and through drive-by malvertising campaigns that identify users of mobile browsers.

The following are some real-world examples of mobile devices being used for cryptojacking:

• During 2014, FireEye iSIGHT Intelligence reported on multiple Android malware apps capable of mining cryptocurrency:
  • In March 2014, Android malware named "CoinKrypt" was discovered, which mined Litecoin, Dogecoin, and CasinoCoin currencies.
  • In March 2014, another form of Android malware – "Android.Trojan.MuchSad.A" or "ANDROIDOS_KAGECOIN.HBT" – was observed mining Bitcoin, Litecoin, and Dogecoin currencies. The malware was disguised as copies of popular applications, including "Football Manager Handheld" and "TuneIn Radio." Variants of this malware have reportedly been downloaded by millions of Google Play users.
  • In April 2014, Android malware named "BadLepricon," which mined Bitcoin, was identified. The malware was reportedly being bundled into wallpaper applications hosted on the Google Play store, at least several of which received 100 to 500 installations before being removed.
  • In October 2014, a type of mobile malware called "Android Slave" was observed in China; the malware was reportedly capable of mining multiple virtual currencies.
• In December 2017, researchers with Kaspersky Labs reported on a new multi-faceted Android malware capable of a variety of actions including mining cryptocurrencies and launching DDoS attacks. The resource load created by the malware has reportedly been high enough that it can cause the battery to bulge and physically destroy the device. The malware, dubbed Loapi, is unique in the breadth of its potential actions. It has a modular framework that includes modules for malicious advertising, texting, web crawling, Monero mining, and other activities. Loapi is thought to be the work of the same developers behind the 2015 Android malware Podec, and is usually disguised as an anti-virus app.
• In January 2018, SophosLabs released a report detailing their discovery of 19 mobile apps hosted on Google Play that contained embedded Coinhive-based cryptojacking code, some of which were downloaded anywhere from 100,000 to 500,000 times.
• Between November 2017 and January 2018, researchers with Malwarebytes Labs reported on a drive-by cryptojacking campaign that affected millions of Android mobile browsers to mine Monero.

Cryptojacking Spam Campaigns

FireEye iSIGHT Intelligence has observed several cryptocurrency miners distributed via spam campaigns, which is a commonly used tactic to indiscriminately distribute malware. We expect malicious actors will continue to use this method to disseminate cryptojacking code as for long as cryptocurrency mining remains profitable.

In late November 2017, FireEye researchers identified a spam campaign delivering a malicious PDF attachment designed to appear as a legitimate invoice from the largest port and container service in New Zealand: Lyttelton Port of Chistchurch (Figure 9). Once opened, the PDF would launch a PowerShell script that downloaded a Monero miner from a remote host. The malicious miner connected to the pools supportxmr.com and nanopool.org.

Figure 9: Sample lure attachment (PDF) that downloads malicious cryptocurrency miner

Additionally, a massive cryptojacking spam campaign was discovered by FireEye researchers during January 2018 that was designed to look like legitimate financial services-related emails. The spam email directed victims to an infection link that ultimately dropped a malicious ZIP file onto the victim's machine. Contained within the ZIP file was a cryptocurrency miner utility (MD5: 80b8a2d705d5b21718a6e6efe531d493) configured to mine Monero and connect to the minergate.com pool. While each of the spam email lures and associated ZIP filenames were different, the same cryptocurrency miner sample was dropped across all observed instances (Table 2).

Table 2: Sampling of observed ZIP filenames delivering cryptocurrency miner

Cryptojacking Worms

Following the WannaCry attacks, actors began to increasingly incorporate self-propagating functionality within their malware. Some of the observed self-spreading techniques have included copying to removable drives, brute forcing SSH logins, and leveraging the leaked NSA exploit EternalBlue. Cryptocurrency mining operations significantly benefit from this functionality since wider distribution of the malware multiplies the amount of CPU resources available to them for mining. Consequently, we expect that additional actors will continue to develop this capability.

The following are some real-world examples of cryptojacking worms:

• In May 2017, Proofpoint reported a large campaign distributing mining malware "Adylkuzz." This cryptocurrency miner was observed leveraging the EternalBlue exploit to rapidly spread itself over corporate LANs and wireless networks. This activity included the use of the DoublePulsar backdoor to download Adylkuzz. Adylkuzz infections create botnets of Windows computers that focus on mining Monero.
• Security researchers with Sensors identified a Monero miner worm, dubbed "Rarogminer," in April 2018 that would copy itself to removable drives each time a user inserted a flash drive or external HDD.
• In January 2018, researchers at F5 discovered a new Monero cryptomining botnet that targets Linux machines. PyCryptoMiner is based on Python script and spreads via the SSH protocol. The bot can also use Pastebin for its command and control (C2) infrastructure. The malware spreads by trying to guess the SSH login credentials of target Linux systems. Once that is achieved, the bot deploys a simple base64-encoded Python script that connects to the C2 server to download and execute more malicious Python code.

Detection Avoidance Methods

Another trend worth noting is the use of proxies to avoid detection. The implementation of mining proxies presents an attractive option for cyber criminals because it allows them to avoid developer and commission fees of 30 percent or more. Avoiding the use of common cryptojacking services such as Coinhive, Cryptloot, and Deepminer, and instead hosting cryptojacking scripts on actor-controlled infrastructure, can circumvent many of the common strategies taken to block this activity via domain or file name blacklisting.

In March 2018, Bleeping Computer reported on the use of cryptojacking proxy servers and determined that as the use of cryptojacking proxy services increases, the effectiveness of ad blockers and browser extensions that rely on blacklists decreases significantly.

Several mining proxy tools can be found on GitHub, such as the XMRig Proxy tool, which greatly reduces the number of active pool connections, and the CoinHive Stratum Mining Proxy, which uses Coinhive’s JavaScript mining library to provide an alternative to using official Coinhive scripts and infrastructure.

In addition to using proxies, actors may also establish their own self-hosted miner apps, either on private servers or cloud-based servers that supports Node.js. Although private servers may provide some benefit over using a commercial mining service, they are still subject to easy blacklisting and require more operational effort to maintain. According to Sucuri researchers, cloud-based servers provide many benefits to actors looking to host their own mining applications, including:

• Available free or at low-cost
• No maintenance, just upload the crypto-miner app
• Harder to block as blacklisting the host address could potentially impact access to legitimate services
• Resilient to permanent takedown as new hosting accounts can more easily be created using disposable accounts

The combination of proxies and crypto-miners hosted on actor-controlled cloud infrastructure presents a significant hurdle to security professionals, as both make cryptojacking operations more difficult to detect and take down.

Mining Victim Demographics

Based on data from FireEye detection technologies, the detection of cryptocurrency miner malware has increased significantly since the beginning of 2018 (Figure 10), with the most popular mining pools being minergate and nanopool (Figure 11), and the most heavily affected country being the U.S. (Figure 12). Consistent with other reporting, the education sector remains most affected, likely due to more relaxed security controls across university networks and students taking advantage of free electricity to mine cryptocurrencies (Figure 13).

Figure 10: Cryptocurrency miner detection activity per month

Figure 11: Commonly observed pools and associated ports

Figure 12: Top 10 affected countries

Figure 13: Top five affected industries

Figure 14: Top affected industries by country

Mitigation Techniques

Unencrypted Stratum Sessions

According to security researchers at Cato Networks, in order for a miner to participate in pool mining, the infected machine will have to run native or JavaScript-based code that uses the Stratum protocol over TCP or HTTP/S. The Stratum protocol uses a publish/subscribe architecture where clients will send subscription requests to join a pool and servers will send messages (publish) to its subscribed clients. These messages are simple, readable, JSON-RPC messages. Subscription requests will include the following entities: id, method, and params (Figure 15). A deep packet inspection (DPI) engine can be configured to look for these parameters in order to block Stratum over unencrypted TCP.

Figure 15: Stratum subscription request parameters

Encrypted Stratum Sessions

In the case of JavaScript-based miners running Stratum over HTTPS, detection is more difficult for DPI engines that do not decrypt TLS traffic. To mitigate encrypted mining traffic on a network, organizations may blacklist the IP addresses and domains of popular mining pools. However, the downside to this is identifying and updating the blacklist, as locating a reliable and continually updated list of popular mining pools can prove difficult and time consuming.

Browser-Based Sessions

Identifying and detecting websites that have embedded coin mining code can be difficult since not all coin mining scripts are authorized by website publishers (as in the case of a compromised website). Further, in cases where coin mining scripts were authorized by a website owner, they are not always clearly communicated to site visitors.

As defenses evolve to prevent unauthorized coin mining activities, so will the techniques used by actors; however, blocking some of the most common indicators that we have observed to date may be effective in combatting a significant amount of the CPU-draining mining activities that customers have reported. Generic detection strategies for browser-based cryptocurrency mining include:

• Blocking domains known to have hosted coin mining scripts
• Blocking websites of known mining project websites, such as Coinhive
• Blocking scripts altogether
• Using an ad-blocker or coin mining-specific browser add-ons
• Detecting commonly used naming conventions
• Alerting and blocking traffic destined for known popular mining pools

Some of these detection strategies may also be of use in blocking some mining functionality included in existing financial malware as well as mining-specific malware families.

It is important to note that JavaScript used in browser-based cryptojacking activity cannot access files on disk. However, if a host has inadvertently navigated to a website hosting mining scripts, we recommend purging cache and other browser data.

Outlook

In underground communities and marketplaces there has been significant interest in cryptojacking operations, and numerous campaigns have been observed and reported by security researchers. These developments demonstrate the continued upward trend of threat actors conducting cryptocurrency mining operations, which we expect to see a continued focus on throughout 2018. Notably, malicious cryptocurrency mining may be seen as preferable due to the perception that it does not attract as much attention from law enforcement as compared to other forms of fraud or theft. Further, victims may not realize their computer is infected beyond a slowdown in system performance.

Due to its inherent privacy-focused features and CPU-mining profitability, Monero has become one of the most attractive cryptocurrency options for cyber criminals. We believe that it will continue to be threat actors' primary cryptocurrency of choice, so long as the Monero blockchain maintains privacy-focused standards and is ASIC-resistant. If in the future the Monero protocol ever downgrades its security and privacy-focused features, then we assess with high confidence that threat actors will move to use another privacy-focused coin as an alternative.

Because of the anonymity associated with the Monero cryptocurrency and electronic wallets, as well as the availability of numerous cryptocurrency exchanges and tumblers, attribution of malicious cryptocurrency mining is very challenging for authorities, and malicious actors behind such operations typically remain unidentified. Threat actors will undoubtedly continue to demonstrate high interest in malicious cryptomining so long as it remains profitable and relatively low risk.