Swedish Windows Security User Group

Dofoil is a sophisticated threat that attempted to install coin miner malware on hundreds of thousands of computers in March, 2018. In previous blog posts we detailed how behavior monitoring and machine learning in Windows Defender AV protected customers from a massive Dofoil outbreak that we traced back to a software update poisoning campaign several weeks prior. Notably, customers of Windows 10 S, a special Windows 10 configuration that provides streamlined Microsoft-verified security, were not affected by the Dofoil outbreak.

In this blog post, we will expound on Dofoils anti-debugging and anti-analysis tactics, and demonstrate how the rich detection libraries of Windows Defender Advanced Threat Protection and Windows Defender Exploit Guard can help during investigation.

We found that Dofoil was designed to be elusive to analysis. It checks its environment and stops running in virtual machine environments. It also checks for various analysis tools and kills them right away. This can make malware analysis and assessment challenging.

The following diagram shows the multi-stage malware execution process, which includes checks for traits of analysis environments during some stages.

Figure 1. Dofoil multi-stage shellcode and payload execution flow

The table below describes the purpose of each stage. The first five stages have at least one or two different techniques that can deter dynamic or static malware analysis.

STAGES	DESCRIPTION
1. Obfuscated wrapper code	Anti-heuristics Anti-emulation
2. Bootstrap module	Performs self-process hollowing to load the next module
3. Anti-debugging module	Performs anti-debugging operation
4. Trojan downloader module	Performs system environment checks Performs anti-VM operation Injects itself to explorer.exe through process hollowing
5. Trojan downloader module in explorer.exe	Contacts C&C server to download trojan and run it using process hollowing technique
6. Payload downloader module in explorer.exe	Contacts C&C server to download the main payload
7. Trojan module	Steals credentials from various application settings and sends stolen into to the C&C server over HTTP channel
8. CoinMiner.D	Mines digital currencies

Table 1. Dofoil’s multi-stage modules

Initial stages

The first three stages (i.e., obfuscated wrapper code, bootstrap module, anti-debugging module) use the following techniques to avoid analysis and identification.

ANTI-ANALYSIS TECHNIQUES	DESCRIPTION
Benign code insertion	Inserts a huge benign code block to confuse heuristics and manual inspection
Anti-emulation	Enumerates an arbitrary registry key (HKEY_CLASSES_ROOT\Interface\{3050F557-98B5-11CF-BB82-00AA00BDCE0B}) and compares the data with an expected value (DispHTMLCurrentStyle) to check if the malware runs inside an emulator
Self-process hollowing	Uses the process hollowing technique on the current process, making analysis extra difficult due to the altered code mapping
Debugger checks	Checks for debuggers, and modifies code to crash. This can add additional layer of confusion to researchers, who are bound to investigate the cause of the crashes. It checks for the PEB.BeingDebugged and PEB.NtGlobalFlag fields in the PEB structure. For example, PEB.BeingDebugged is set to 1 and PEB.NtGlobalFlag is set to FLG_HEAP_ENABLE_TAIL_CHECK|FLG_HEAP_ENABLE_FREE_CHECK| FLG_HEAP_VALIDATE_PARAMETERS when a debugger is attached to the process.

Table 2. Anti-analysis techniques

The first stage contains some benign-looking code before the actual malicious code. This can give the executable a harmless appearance. It can also make the emulation of the code difficult because emulating various API calls that are not present in many malware codes can be challenging.

The first-stage code also performs a registry key enumeration to make sure it has the expected value. When all checks are passed, it decodes the second-stage shellcode and runs it on the allocated memory. This shellcode un-maps the original main modules memory, and then decodes the third-stage shellcode into that memory this is known as a self-process hollowing technique.

Figure 2. Self-modification based on PEB.BeingDebugged value

Windows Defender ATPs process tree can help with investigation by exposing these anti-debugging techniques.

Figure 3. Windows Defender ATP process tree showing anti-debugging techniques

Trojan downloader module

The trojan downloader module performs various environment checks, including virtual environment and analysis tool checks, before downloading the payload.

ANTI-ANALYSIS TECHNIQUES	DESCRIPTION
Check module name	Checks if the main executable name contains the string “sample”
Check volume serial	Checks if current volume serial number is 0xCD1A40 or 0x70144646
Check modules	Checks the presence of DLLs related to debuggers
Check disk-related registry keys	Checks the value of the registry key HKLM\System\CurrentControlSet\Services\Disk\Enum against well-known disk name patterns for virtual machines (qemu, virtual, vmware, xen, ffffcce24)
Process check	Checks running processes and kills those with processes names associated with analysis tools (procexp.exe, procexp64.exe, procmon.exe, procmon64.exe, tcpview.exe, wireshark.exe, processhacker.exe, ollydbg.exe, idaq.exe, x32dbg.exe)
Windows class name check	Checks the current Windows class names and exits when some well-known names are found (Autoruns, PROCEXPL, PROCMON_WINDOW_CLASS, TCPViewClass, ProcessHacker, OllyDbg, WinDbgFrameClass)

Table 3. Anti-analysis techniqueof Dofoil’s trojan downloader module

The list of target process names and Windows class names exist in custom checksum form. The checksum algorithm looks like the following:

Figure 4. Shift and XOR custom checksum algorithm

The purpose of this checksum is to prevent malware researchers from quickly figuring out what analysis tools it detects, making analysis more time-consuming.

STRING	CHECKSUM
Autoruns	0x0E5C1C5D
PROCEXPL	0x1D421B41
PROCMON_WINDOW_CLASS	0x4B0C105A
TCPViewClass	0x1D4F5C43
ProcessHacker	0x571A415E
OllyDbg	0x4108161D
WinDbgFrameClass	0x054E1905
procexp.exe	0x19195C02
procexp64.exe	0x1C0E041D
procmon.exe	0x06185D0B
procmon64.exe	0x1D07120A
tcpview.exe	0x060B5118
wireshark.exe	0x550E1E0D
processhacker.exe	0x51565C47
ollydbg.exe	0x04114C14
x32dbg.exe	0x5F4E5C04
idaq.exe	0x14585A12

Table 4. String checksum table used for process names and Windows class names

Process hollowing

Dofoil heavily uses the process hollowing technique. Its main target for process hollowing is explorer.exe. The Dofoil shellcode launches a new instance of explorer.exe, allocates shellcode in heap region, and then modifies the entry point code to jump into the shellcode. This way, the malware avoids using CreateRemoteThread API, but can still achieve code injection.

Figure 5. Modification of explorer.exe entry point code

Windows Defender ATP can detect the process hollowing behavior with advanced memory signals. The following process tree shows that the malware injects itself into explorer.exe using the process hollowing technique.

Figure 6. Windows Defender ATP alert process tree showing the first process hollowing

When the shellcode downloads another layer of payload, it spawns another explorer.exe to inject the payload into using process hollowing. Windows Defender ATP can save analysis time on these cases by pinpointing the malicious actions, eliminating the need for guessing what these newly spawned Windows system processes are doing.

Figure 7. Windows Defender ATP alert process tree showing the second process hollowing

The process hollowing behavior can be detected through Exploit protection in Windows Defender Exploit Guard. This can be done by enabling the Export Address Filter (EAF) mitigation against explorer.exe. The detection happens when the shellcode goes through the export addresses of the modules to find the export address of the LoadLibraryA and GetProcAddress functions.

Figure 8. Export Address Filter (EAF) event exposed in Event viewer

Windows Defender Exploit Guard events are also exposed in the Windows Defender ATP portal:

Figure 9. Windows Defender ATP view of the Windows Defender Exploit Guard event

Adding Windows Defender Exploit Guard EAF audit/block policy to common system processes like explorer.exe, cmd.exe, or verclsid.exe can be useful in finding and blocking process hollowing or process injection techniques commonly used by malware. This policy can impact third-party apps that may behave like shellcode, so we recommend testing Windows Defender Exploit Guard with audit mode enabled before enforcement.

Command-and-control (C&C) and NameCoin domains

Dofoils C&C connection is very cautious. The trojan code first tries to connect to well-known web pages and verifies that the malware has proper and real Internet connection, not simulated as in test environments. After it makes sure it has a real Internet connection, the malware makes HTTP connections to the actual C&C servers.

Figure 10. Access to known servers to confirm Internet connectivity

The malware uses NameCoin domain name servers. NameCoin is a decentralized name server system that provides extra privacy backed by blockchain technology. Except for the fact that the DNS client needs to use specific sets of NameCoin DNS servers, the overall operation is very similar to a normal DNS query. Because NameCoin uses blockchain technology, you can query the history of the domain name changes through blocks.

Figure 11. Malicious hostname DNS entry changes over time (https://namecha.in/name/d/vrubl)

Windows Defender ATP can provide visibility into the malwares network activities. The following alert process tree shows the malwares .bit domain resolution activity and, after that, the connections to the resolved C&C servers. You can also view other activities from the executable, for example, its connections to other servers using SMTP ports.

Figure 12. Windows Defender ATP alert process tree showing C&C server connection through NameCoin server name resolution

The Windows Defender ATP advanced hunting feature, which is currently in preview, can be used to hunt down more malware samples that possibly abuse NameCoin servers. For example, the following query will let you view recent connections observed in the network. This can lead to extra insights on other threats that use the same NameCoin servers.

Figure 13. Advanced hunting for other threats using the same NameCoin servers

The purpose of using NameCoin is to prevent easy sinkholing of the domains. Because there are no central authorities on the NameCoin domain name records, it is not possible for the authorities to change the domain record. Also, malware abusing NameCoin servers use massive numbers of NameCoin DNS servers to make full shutdown of those servers very difficult.

Conclusion

Dofoil is a very evasive malware. It has various system environment checks and tests Internet connectivity to make sure it runs on real machines, not in analysis environments or virtual machines. This can make the analysis time-consuming and can mislead malware analysis systems.

In attacks like the Dofoil outbreak, Windows Defender Advanced Threat Protection (Windows Defender ATP) can help network defenders analyze the timeline from the victim machine and get rich information on process execution flow, C&C connections, and process hollowing activities. Windows Defender ATP can be used as an analysis platform with fine-tuned visibility into system activities when set up in a lab environment. This can save time and resource during malware investigation.

In addition, Windows Defender Exploit Guard can be useful in finding malicious shellcodes that traverse export address tables. Windows Defender Exploit Guard can be an excellent tool for finding and blocking malware and exploit activities.

Windows Defender Exploit Guard events are surfaced in the Windows Defender ATP portal, which integrates protections from other Microsoft solutions, including Windows Defender AV and Windows Defender Application Guard. This integrated security management experience makes Windows Defender ATP a comprehensive solution for detecting and responding to a wide range of malicious activities across the network.

Windows 10 S, a special configuration of Windows 10, locks down devices against Dofoil and other attacks by working exclusively with apps from the Microsoft Store and using Microsoft Edge as the default browser. This streamlined, Microsoft-verified platform seals common malware entry points.

To test how Windows Defender ATP can help your organization detect, investigate, and respond to advanced attacks, sign up for a free trial.

 

 

Matt Oh, Stefan Sellmer, Jonathan Bar Or, Mark Wodrich
Windows Defender ATP Research

 

 

Indicators of compromise (IoCs)

TrojanDownloader:Win32/Dofoil.AB:

d191ee5b20ec95fe65d6708cbb01a6ce72374b309c9bfb7462206a0c7e039f4d

eaa63f6b500afedcaeb8d5b18a08fd6c7d95695ea7961834b974e2a653a42212

cded7aedca6b54a6d4273153864a25ccad35cba5cafeaec828a6ad5670a5973a

Trojan:Win32/Dofoil.AB:

070243ad7fb4b3c241741e564039c80ca65bfdf15daa4add70d5c5a3ed79cd5c

5f3efdc65551edb0122ab2c40738c48b677b1058f7dfcdb86b05af42a2d8299C

28ce9763a808c4a7509e9bf92d9ca80212a241dfa1aecd82caedf1f101eac692

5d7875abbbf104f665a0ee909c372e1319c5157dfc171e64ac2bc8b71766537f

Trojan:Win32/CoinMiner.D

2b83c69cf32c5f8f43ec2895ec9ac730bf73e1b2f37e44a3cf8ce814fb51f12

C&C URLs:

hxxp://levashov.bit/15022018/

hxxp://vrubl.bit/15022018/

C&C server:

vinik.bit

Related .bit domains (updated in same block as C&C server):

henkel.bit

makron.bit

makronwin.bit

NameCoin servers used by Dofoil:

139.59.208.246

130.255.73.90

31.3.135.232

52.174.55.168

185.121.177.177

185.121.177.53

62.113.203.55

144.76.133.38

169.239.202.202

5.135.183.146

142.0.68.13

103.253.12.18

62.112.8.85

69.164.196.21

107.150.40.234

162.211.64.20

217.12.210.54

89.18.27.34

193.183.98.154

51.255.167.0

91.121.155.13

87.98.175.85

185.97.7.7

 

 

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On March 7, we reported that a massive Dofoil campaign attempted to install malicious cryptocurrency miners on hundreds of thousands of computers. Windows Defender Antivirus, with its behavior monitoring, machine learning technologies, and layered approach to security detected and blocked the attack within milliseconds.Windows 10 S, a special configuration of Windows 10 providing Microsoft-verified security, was not vulnerable to this attack.

Immediately upon discovering the attack, we looked into the source of the huge volume of infection attempts. Traditionally, Dofoil (also known as Smoke Loader) is distributed in multiple ways, including spam email and exploit kits. In the outbreak, which began in March 6, a pattern stood out: most of the malicious files were written by a process called mediaget.exe.

This process is related to MediaGet, a BitTorrent client that we classify as potentially unwanted application (PUA). MediaGet is often used by people looking to download programs or media from websites with dubious reputation. Downloading through peer-to-peer file-sharing apps like this can increase the risk of downloading malware.

During the outbreak, however, Dofoil didnt seem to be coming from torrent downloads. We didnt see similar patterns in other file-sharing apps. The process mediaget.exe always wrote the Dofoil samples to the %TEMP% folder using the file name my.dat. The most common source of infection was the file %LOCALAPPDATA%\MediaGet2\mediaget.exe (SHA-1: 3e0ccd9fa0a5c40c2abb40ed6730556e3d36af3c).

Tracing the infection timeline

Our continued investigation on the Dofoil outbreak revealed that the March 6 campaign was a carefully planned attack with initial groundwork dating back to mid-February. To set the stage for the outbreak, attackers performed an update poisoning campaign that installed a trojanized version of MediaGet on computers. The following timeline shows the major events related to the Dofoil outbreak.

Figure 1.MediaGet-related malware outbreak timeline (all dates in UTC).

MediaGet update poisoning

The update poisoning campaign that eventually led to the outbreak is described in the following diagram. A signed mediaget.exe downloads an update.exe program and runs it on the machine to install a new mediaget.exe. The new mediaget.exe program has the same functionality as the original but with additional backdoor capability.

Figure 2. Update poisoning flow

The malicious update process is recorded by Windows Defender ATP. The following alert process tree shows the original mediaget.exe dropping the poisoned signed update.exe.

Figure 3. Windows Defender ATP detection of malicious update process

Poisoned update.exe

The dropped update.exe is a packaged InnoSetup SFX which has an embedded trojanized mediaget.exe, update.exe. When run, it drops a trojanized unsigned version of mediaget.exe.

Figure 4.Certificate information of the poisoned update.exe

Update.exe is signed by a third-party developer company completely unrelated with MediaGet and probably also victim of this plot; update.exe was code signed with a different cert just to pass the signing requirement verification as seen in the original mediaget.exe. The update code will check the certificate information to verify whether it is valid and signed. If it is signed, it will check that the hash value matches the value retrieved from the hash server located in mediaget.com infrastructure. The figure below shows a code snippet that checks for valid signatures on the downloaded update.exe.

Figure 5. mediaget.exe update code

Trojanized mediaget.exe

The trojanized mediaget.exe file, detected by Windows Defender AV as Trojan:Win32/Modimer.A, shows the same functionality as the original one, but it is not signed by any parties and has additional backdoor functionality. This malicious binary has 98% similarity to the original, clean MediaGet binary. The following PE information shows the different PDB information and its file path left in the executable.

Figure 6. PDB path comparison of signed and trojanized executable

When the malware starts, it builds a list of command-and-control (C&C) servers.

Figure 7. C&C server list

One notable detail about the embedded C&C list is that the TLD .bit is not an ICANN-sanctioned TLD and is supported via NameCoin infrastructure. NameCoin is a distributed name server system that adopts the concept of blockchain model and provides anonymous domains. Since .bit domains cant be resolved by ordinary DNS servers, the malware embeds a list of 71 IPv4 addresses that serve as NameCoin DNS servers.

The malware then uses these NameCoin servers to perform DNS lookups of the .bit domains. From this point these names are in the machine’s DNS cache and future lookups will be resolved without needing to specify the NameCoin DNS servers.

The first contact to the C&C server starts one hour after the program starts.

Figure 8. C&C connection start timer

The malware picks one of the four C&C servers at random and resolves the address using NameCoin if its a .bit domain. It uses HTTP for command-and-control communication.

Figure 9. C&C server connection

The backdoor code collects system information and sends them to the C&C server through POST request.

Figure 10. System information

The C&C server sends back various commands to the client. The following response shows the HASH, IDLE, and OK commands. The IDLE command makes the process wait a certain time, indicated in seconds (for example, 7200 seconds = 2 hours), before contacting C&C server again.

Figure 11. C&C commands

One of the backdoor commands is a RUN command that retrieves a URL from the C&C server command string. The malware then downloads a file from the URL, saves it as %TEMP%\my.dat, and runs it.

Figure 12. RUN command processing code

This RUN command was used for the distribution of the Dofoil malware starting March 1 and the malware outbreak on March 6. Windows Defender ATP alert process tree shows the malicious mediaget.exe communicating with goshan.online, one of the identified C&C servers. It then drops and runs my.dat (Dofoil), which eventually leads to the CoinMiner component.

Figure 13.Dofoil, CoinMiner download and execution flow

Figure 14. Windows Defender ATP alert process tree

The malware campaign used Dofoil to deliver CoinMiner, which attempted to use the victims computer resources to mine cryptocurrencies for the attackers. The Dofoil variant used in the attack showed advanced cross-process injection techniques, persistence mechanisms, and evasion methods. Windows Defender ATP can detect these behaviors across the infection chain.

Figure 15. Windows Defender ATP detection for Dofoils process hollowing behavior

We have shared details we uncovered in our investigation with MediaGets developers to aid in their analysis of the incident.

We have shared details of the malicious use of code-signing certificate used in update.exe (thumbprint: 5022EFCA9E0A9022AB0CA6031A78F66528848568) with the certificate owner.

Real-time defense against malware outbreaks

The Dofoil outbreak on March 6, which was built on prior groundwork, exemplifies the kind of multi-stage malware attacks that are fast-becoming commonplace. Commodity cybercrime threats are adopting sophisticated methods that are traditionally associated with more advanced cyberattacks. Windows Defender Advanced Threat Protection (Windows Defender ATP) provides the suite of next-gen defenses that protect customers against a wide range of attacks in real-time.

Windows Defender AV enterprise customers who have enabled the potentially unwanted application (PUA) protection feature were protected from the trojanized MediaGet software that was identified as the infection source of the March 6 outbreak.

Windows Defender AV protected customers from the Dofoil outbreak at the onset. Behavior-based detection technologies flagged Dofoils unusual persistence mechanism and immediately sent a signal to the cloud protection service, where multiple machine learning models blocked most instances at first sight.

In our in-depth analysis of the outbreak, we also demonstrated that the rich detection libraries in Windows Defender ATP flagged Dofoils malicious behaviors throughout the entire infection process. These behaviors include code injection, evasion methods, and dropping a coin mining component. Security operations can use Windows Defender ATP to detect and respond to outbreaks. Windows Defender ATP also integrates protections from Windows Defender AV, Windows Defender Exploit Guard, and Windows Defender Application Guard, providing a seamless security management experience.

For enhanced security against Dofoil and others similar coin miners, Microsoft recommends Windows 10 S. Windows 10 S exclusively runs apps from the Microsoft Store, effectively blocking malware and applications from unverified sources. Windows 10 S users were not affected by this Dofoil campaign.

Windows Defender Research

Indicators of compromise (IOCs)

File name	SHA-1	Description	Signer	Signing date	Detection name
mediaget.exe	1038d32974969a1cc7a79c3fc7b7a5ab8d14fd3e	Offical mediaget.exe executable	GLOBAL MICROTRADING PTE. LTD.	2:04 PM 10/27/2017	PUA:Win32/MediaGet
mediaget.exe	4f31a397a0f2d8ba25fdfd76e0dfc6a0b30dabd5	Offical mediaget.exe executable	GLOBAL MICROTRADING PTE. LTD.	4:24 PM 10/18/2017	PUA:Win32/MediaGet
update.exe	513a1624b47a4bca15f2f32457153482bedda640	Trojanized updater executable	DEVELTEC SERVICES SA DE CV	N/A	Trojan:Win32/Modimer.A
mediaget.exe	3e0ccd9fa0a5c40c2abb40ed6730556e3d36af3c, fda5e9b9ce28f62475054516d0a9f5a799629ba8	Trojanized mediaget.exe executable	Not signed	N/A	Trojan:Win32/Modimer.A
my.dat	d84d6ec10694f76c56f6b7367ab56ea1f743d284	Dropped malicious executable			TrojanDownloader:Win32/Dofoil.AB
wuauclt.exe	88eba5d205d85c39ced484a3aa7241302fd815e3	Dropped CoinMiner			Trojan:Win32/CoinMiner.D

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The surge in Bitcoin prices has driven widescale interest in cryptocurrencies. While the future of digital currencies is uncertain, they are shaking up the cybersecurity landscape as they continue to influence the intent and nature of attacks.

Cybercriminals gave cryptocurrencies a bad name when ransomware started instructing victims to pay ransom in the form of digital currencies, most notably Bitcoin, the first and most popular of these currencies. It was not an unexpected move digital currencies provide the anonymity that cybercriminals desire. The sharp increase in the value of digital currencies is a windfall for cybercriminals who have successfully extorted Bitcoins from ransomware victims.

These dynamics are driving cybercriminal activity related to cryptocurrencies and have led to an explosion of cryptocurrency miners (also called cryptominers or coin miners) in various forms. Mining is the process of running complex mathematical calculations necessary to maintain the blockchain ledger. This process rewards coins but requires significant computing resources.

Coin miners are not inherently malicious. Some individuals and organizations invest in hardware and electric power for legitimate coin mining operations. However, others are looking for alternative sources of computing power; as a result, some coin miners find their way into corporate networks. While not malicious, these coin miners are not wanted in enterprise environments because they eat up precious computing resources.

As expected, cybercriminals see an opportunity to make money and they customize coin miners for malicious intents. Crooks then run malware campaigns that distribute, install, and run the trojanized miners at the expense of other peoples computing resources. On March 6, Windows Defender Advanced Threat Protection (Windows Defender ATP) blocked a massive coin mining campaign from the operators of Dofoil (also known as Smoke Loader).

In enterprise environments, Windows Defender ATP provides the next-gen security features, behavioral analysis, and cloud-powered machine learning to help protect against the increasing threats of coin miners: Trojanized miners, mining scripts hosted in websites, and even legitimate but unauthorized coin mining applications.

Coin mining malware

Cybercriminals repackage or modify existing miners and then use social engineering, dropper malware, or exploits to distribute and install the trojanized cryptocurrency miners on target computers. Every month from September 2017 to January 2018, an average of 644,000 unique computers encountered coin mining malware.

Figure 1. Volume of unique computers that encountered trojanized coin miners

Interestingly, the proliferation of malicious cryptocurrency miners coincide with a decrease in the volume of ransomware. Are these two trends related? Are cybercriminals shifting their focus to cryptocurrency miners as primary source of income? Its not likely that cybercriminals will completely abandon ransomware operations any time soon, but the increase in trojanized cryptocurrency miners indicates that attackers are definitely exploring the possibilities of this newer method of illicitly earning money.

We have seen a wide range of malicious cryptocurrency miners, some of them incorporating more sophisticated mechanisms to infect targets, including the use of exploits or self-distributing malware. We have also observed that established malware families long associated with certain modus operandi, such as banking trojans, have started to include coin mining routines in recent variants. These developments indicate widespread cybercriminal interest in coin mining, with various attackers and cybercriminal groups launching attacks.

Infection vectors

The downward trend in ransomware encounters may be due to an observed shift in the payload of one of its primary infection vectors: exploit kits. Even though there has been a continuous decrease in the volume of exploit kit activity since 2016, these kits, which are available as a service in cybercriminal underground markets, are now also being used to distribute coin miners. Before ransomware, exploit kits were known to deploy banking trojans.

DDE exploits, which have also been known to distribute ransomware, are now delivering miners. For example, a sample of the malware detected as Trojan:Win32/Coinminer (SHA-256: 7213cbbb1a634d780f9bb861418eb262f58954e6e5dca09ca50c1e1324451293) is installed by Exploit:O97M/DDEDownloader.PA, a Word document that contains the DDE exploit. The exploit launches a cmdlet that executes a malicious PowerShell script (Trojan:PowerShell/Maponeir.A), which then downloads the trojanized miner: a modified version of the miner XMRig, which mines Monero cryptocurrency.

Other miners use reliable social engineering tactics to infect machines. Cybercriminals have been distributing a file called flashupdate, masquerading the file as the Flash Player. The download link itselfseen in spam campaigns and malicious websitesalso uses the string flashplayer. Detected as Trojan:Win32/Coinminer, this trojanized coin miner (SHA-256 abbf959ac30d23cf2882ec223966b0b8c30ae85415ccfc41a5924b29cd6bd4db) likewise uses a modified version of the XMRig miner.

Persistence mechanisms

For cryptocurrency miners, persistence is a key element. The longer they stay memory-resident and undetected, the longer they can mine using stolen computer resources. While more traditional persistence mechanisms like scheduled tasks and autostart registry entries are common, cybercriminals can also use more advanced methods like code injection and other fileless techniques, which can allow them to evade detection.

One example of coin mining malware that uses code injection is a miner detected as Trojan:Win32/CoinMiner.BW!bit (SHA-256: f9c67313230bfc45ba8ffe5e6abeb8b7dc2eddc99c9cebc111fcd7c50d11dc80), which spawns an instance of notepad.exe and then injects its code. Once in memory, it uses some binaries related to legitimate cryptocurrency miners but runs them using specific parameters so that coins are sent to the attackers wallet.

We also came across a malicious PowerShell script, detected as TrojanDownloader:PowerShell/CoinMiner (SHA-256: 5d7e0fcf45004a7a4e27dd42c131bcebfea04f14540bd0f17635505b42a96d6e), that downloads mining code that it executes using its own parameters. It adds a scheduled task so that it runs every time the computer starts.

Spreading capabilities and other behaviors

Some coin miners have other capabilities. For example, a miner detected as Worm:Win32/NeksMiner.A (SHA-256: 80f098ac43f17dbd0f7bb6bad719cc204ef76015cbcdae7b28227c4471d99238) drops a copy in the root folder of all available drives, including mapped network drives and removable drives, allowing it to spread as these drives are accessed using other computers. It then runs legitimate cryptocurrency miners but using its own parameters.

As trojanized cryptocurrency miners continue evolving to become the monetization tool of choice for cybercriminals, we can expect the miners to incorporate more behaviors from established threat types.

Browser-based coin miners (cryptojacking)

Coin mining scripts hosted on websites introduced a new class of browser-based threats a few years ago. The increased interest in cryptocurrencies has intensified this trend. When the said websites are accessed, the malicious scripts mine coins using the visiting devices computing power. While some websites claim legitimacy by prompting the visitor to allow the coin mining script to run, others are more dubious.

Some of these websites, usually video streaming sites, appear to have been set up by cybercriminals specifically for coin mining purposes. Others have been compromised and injected with the offending scripts. One such coin miner is hidden in multiple layers of iframes.

Figure 2. A sample coin mining script hidden in multiple layers of iframes in compromised websites

We have also seen have seen tech support scam websites that double as coin miners. Tech support scam websites employ techniques that can make it difficult to close the browser. Meanwhile, a coin mining script runs in the background and uses computer resources.

Figure 3. A sample tech support scam website with a coin mining script

Unauthorized use of legitimate coin miners

On top of malware and malicious websites, enterprises face the threat of another form of cryptocurrency miners: legitimate but unauthorized miners that employees and other parties sneak in to take advantage of sizable processing power in enterprise environments.

While the presence of these miners in corporate networks dont necessarily indicate a bigger attack, they are becoming a corporate issue because they consume precious computing resources that are meant for critical business processes. Miners in corporate networks also result in additional energy consumption, leading to unnecessary costs. Unlike their trojanized counterparts, which arrive through known infection methods, non-malicious but unauthorized cryptocurrency miners might be trickier to detect and block.

In January 2018, Windows enterprise customers who have enabled the potentially unwanted application (PUA) protection feature encountered coin miners in more than 1,800 enterprise machines, a huge jump from the months prior. We expect this number to grow exponentially as we heighten our crackdown on these unwanted applications.

Figure 4. Volume of unique computers in enterprise environments with PUA protection enabled that encountered unauthorized coin miners

While non-malicious, miners classified as potentially unwanted applications (PUA) are typically unauthorized for use in enterprise environments because they can adversely affect computer performance and responsiveness. In contrast, trojanized miners are classified as malware; as such, they are automatically detected and blocked by Microsoft security products. Potentially unwanted applications are further differentiated from unwanted software, which are also considered malicious because they alter your Windows experience without your consent or control.

Apart from coin mining programs, potentially unwanted applications include:

• Programs that install other unrelated programs during installation, especially if those other programs are also potentially unwanted applications
• Programs that hijack web browsing experience by injecting ads to pages
• Driver and registry optimizers that detect issues, request payment to fix the errors, and remain on the computer
• Programs that run in the background and are used for market research

PUA protection is enabled by default in System Center Configuration Manager. Security administrators can also enable and configure the PUA protection feature using PowerShell cmdlets or Microsoft Intune.

Windows Defender AV blocks potentially unwanted applications when a user attempts to download or install the application and if the program file meets one of several conditions. Potentially unwanted applications that are blocked appear in the quarantine list in the Windows Defender Security Center app.

In September 2017, around 2% of potentially unwanted applications blocked by Windows Defender AV are coin miners. This figure has increased to around 6% in January 2018, another indication of the increase of these unwanted applications in corporate networks.

Figure 5. Breakdown of potentially unwanted applications

Protecting corporate networks from cryptocurrency miners

Windows 10 Enterprise customers benefit from Windows Defender Advanced Threat Protection, a wide and robust set of security features and capabilities that help prevent coin minters and other malware.

Windows Defender AV uses multiple layers of protection to detect new and emerging threats. Non-malicious but unauthorized miners can be blocked using the PUA protection feature in Windows Defender AV. Enterprises can also use Windows Defender Application Control to set code integrity policies that prevent employees from installing malicious and unauthorized applications.

Trojanized cryptocurrency miners are blocked by the same machine learning technologies, behavior-based detection algorithms, generics, and heuristics that allow Window Defender AV to detect most malware at first sight and even stop malware outbreaks, such as the massive Dofoil coin miner campaign. By leveraging Antimalware Scan Interface (AMSI), which provides the capability to inspect script malware even with multiple layers of obfuscation, Windows Defender AV can also detect script-based coin miners.

Coin mining malware with more sophisticated behaviors or arrival methods like DDE exploit and malicious scripts launched from email or Office apps can be mitigated using Windows Defender Exploit Guard, particularly its Attack surface reduction and Exploit protection features.

Malicious websites that host coin miners, such as tech support scam pages with mining scripts, can be blocked by Microsoft Edge using Windows Defender SmartScreen and Windows Defender AV.

Corporate networks face the threat of both non-malicious and trojanized cryptocurrency miners. Windows 10 S, a special configuration of Windows 10, can help prevent threats like coin miners and other malware by working exclusively with apps from the Microsoft Store and by using Microsoft Edge as the default browser, providing Microsoft-verified security.

Security operations personnel can use the advanced behavioral and machine learning detection libraries in Windows Defender Endpoint Detection and Response (Windows Defender EDR) to detect coin mining activity and other anomalies in the network.

Figure 6. Windows Defender EDR detection for coin mining malware

Windows Defender EDR integrates detections from Windows Defender AV, Windows Defender Exploit Guard, and other Microsoft security products, providing seamless security management that can allow security operations personnel to centrally detect and respond to cryptocurrency miners and other threats in the network.

 

Alden Pornasdoro, Michael Johnson, and Eric Avena
Windows Defender Research

 

 

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