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	"id": "3c24a70e-f799-48e7-8cd1-e56bc3591ec5",
	"created_at": "2026-04-10T03:21:31.996591Z",
	"updated_at": "2026-04-12T02:21:48.587952Z",
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	"title": "Analyzing attacks taking advantage of the Exchange Server vulnerabilities",
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	"authors": "",
	"file_creation_date": "0001-01-01T00:00:00Z",
	"file_modification_date": "0001-01-01T00:00:00Z",
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	"plain_text": "Analyzing attacks taking advantage of the Exchange Server\r\nvulnerabilities\r\nBy Microsoft Threat Intelligence\r\nPublished: 2021-03-25 · Archived: 2026-04-10 03:02:14 UTC\r\nMicrosoft continues to monitor and investigate attacks exploiting the recent on-premises Exchange Server\r\nvulnerabilities. These attacks are now performed by multiple threat actors ranging from financially motivated\r\ncybercriminals to state-sponsored groups. To help customers who are not able to immediately install updates, Microsoft\r\nreleased a one-click tool that automatically mitigates one of the vulnerabilities and scans servers for known attacks.\r\nMicrosoft also built this capability into Microsoft Defender Antivirus, expanding the reach of the mitigation. As of today,\r\nwe have seen a significant decrease in the number of still-vulnerable servers – more than 92% of known worldwide\r\nExchange IPs are now patched or mitigated. We continue to work with our customers and partners to mitigate the\r\nvulnerabilities.\r\nAs organizations recover from this incident, we continue to publish guidance and share threat intelligence to help detect\r\nand evict threat actors from affected environments. Today, we are sharing intelligence about what some attackers did\r\nafter exploiting the vulnerable servers, ranging from ransomware to data exfiltration and deployment of various second-stage payloads. This blog covers:\r\nThreat intelligence and technical details about known attacks, including components and attack paths, that\r\ndefenders can use to investigate whether on-premises Exchange servers were compromised before they were\r\npatched and to comprehensively respond to and remediate these threats if they see them in their environments.\r\nDetection and automatic remediation built into Microsoft Defender Antivirus and how investigation and\r\nremediation capabilities in solutions like Microsoft Defender for Endpoint can help responders perform additional\r\nhunting and remediate threats.\r\nAlthough the overall numbers of ransomware have remained extremely small to this point, it is important to remember\r\nthat these threats show how quickly attackers can pivot their campaigns to take advantage of newly disclosed\r\nvulnerabilities and target unpatched systems, demonstrating how critical it is for organizations to apply security updates\r\nas soon as possible. We strongly urge organizations to identify and update vulnerable on-premises Exchange servers, and\r\nto follow mitigation and investigation guidance that we have collected and continue to update here:\r\nhttps://aka.ms/ExchangeVulns.\r\nMitigating post-exploitation activities\r\nThe first known attacks leveraging the Exchange Server vulnerabilities were by the nation-state actor HAFNIUM, which\r\nwe detailed in this blog. In the three weeks after the Exchange server vulnerabilities were disclosed and the security\r\nupdates were released, Microsoft saw numerous other attackers adopting the exploit into their toolkits. Attackers are\r\nknown to rapidly work to reverse engineer patches and develop exploits. In the case of a remote code execution (RCE)\r\nvulnerability, the rewards are high for attackers who can gain access before an organization patches, as patching a\r\nsystem does not necessarily remove the access of the attacker.\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 1 of 18\n\nFigure 1. The Exchange Server exploit chain\r\nIn our investigation of the on-premises Exchange Server attacks , we saw systems being affected by multiple threats.\r\nMany of the compromised systems have not yet received a secondary action, such as human-operated ransomware\r\nattacks or data exfiltration, indicating attackers could be establishing and keeping their access for potential later actions.\r\nThese actions might involve performing follow-on attacks via persistence on Exchange servers they have already\r\ncompromised, or using credentials and data stolen during these attacks to compromise networks through other entry\r\nvectors.\r\nAttackers who included the exploit in their toolkits, whether through modifying public proof of concept exploits or their\r\nown research, capitalized on their window of opportunity to gain access to as many systems as they could. Some\r\nattackers were advanced enough to remove other attackers from the systems and use multiple persistence points to\r\nmaintain access to a network.\r\nWe have built protections against these threats into Microsoft security solutions. Refer to the Appendix for a list of\r\nindicators of compromise, detection details, and advanced hunting queries. We have also provided additional tools and\r\ninvestigation and remediation guidance here: https://aka.ms/exchange-customer-guidance.\r\nWhile performing a full investigation on systems is recommended, the following themes are common in many of the\r\nattacks. These are prevailing threat trends that Microsoft has been monitoring, and existing solutions and\r\nrecommendations for prevention and mitigation apply:\r\nWeb shells – As of this writing, many of the unpatched systems we observed had multiple web shells on them.\r\nMicrosoft has been tracking the rise of web shell attacks for the past few years, ensuring our products detect these\r\nthreats and providing remediation guidance for customers. For more info on web shells, read Web shell attacks\r\ncontinue to rise. We have also published guidance on web shell threat hunting with Azure Sentinel.\r\nHuman-operated ransomware – Ransomware attacks pose some of the biggest security risks for organizations\r\ntoday, and attackers behind these attacks were quick to take advantage of the on-premises Exchange Server\r\nvulnerabilities. Successfully exploiting the vulnerabilities gives attackers the ability to launch human-operated\r\nransomware campaigns, a trend that Microsoft has been closely monitoring. For more information about human-operated ransomware attacks, including Microsoft solutions and guidance for improving defenses, read: Human-operated ransomware attacks.\r\nCredential theft – While credential theft is not the immediate goal of some of these attacks, access to Exchange\r\nservers allowed attackers to access and potentially steal credentials present on the system. Attackers can use these\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 2 of 18\n\nstolen credentials for follow-on attacks later, so organizations need to prioritize identifying and remediating\r\nimpacted identities. For more information, read best practices for building credential hygiene.\r\nIn the following sections, we share our analysis of known post-compromise activities associated with exploitation of the\r\nExchange server vulnerabilities because it is helpful to understand these TTPs, in order to defend against other actors\r\nusing similar tactics or tools. While levels of disruptive post-compromise activity like ransomware may be limited at the\r\ntime of this writing, Microsoft will continue to track this space and share information with the community. It’s important\r\nto note that with some post-compromise techniques, attackers may gain highly privileged persistent access, but many of\r\nthe impactful subsequent attacker activities can be mitigated by practicing the principle of least privilege and\r\nmitigating lateral movement.\r\nDoejoCrypt ransomware\r\nDoejoCrypt was the first ransomware to appear to take advantage of the vulnerabilities, starting to encrypt in limited\r\nnumbers shortly after the patches were released. Ransomware attackers often use multiple tools and exploits to gain\r\ninitial access, including purchasing access through a broker or “reseller” who sells access to systems they have already\r\ncompromised. The DoejoCrypt attacks start with a variant of the Chopper web shell being deployed to the Exchange\r\nserver post-exploitation.\r\nThe web shell writes a batch file to C:\\Windows\\Temp\\xx.bat. Found on all systems that received the DoejoCrypt\r\nransomware payload, this batch file performs a backup of the Security Account Manager (SAM) database and the\r\nSystem and Security registry hives, allowing the attackers later access to passwords of local users on the system and,\r\nmore critically, in the LSA Secrets portion of the registry, where passwords for services and scheduled tasks are stored.\r\nFigure 2. xx.bat\r\nGiven configurations that administrators typically use on Exchange servers, many of the compromised systems are likely\r\nto have had at least one service or scheduled task configured with a highly privileged account to perform actions like\r\nbackups. As service account credentials are not frequently changed, this could provide a great advantage to an\r\nattacker even if they lose their initial web shell access due to an antivirus detection, as the account can be used to\r\nelevate privileges later, which is why we strongly recommend operating under the principle of least privileged access.\r\nThe batch file saves the registry hives to a semi-unique location, C:\\windows\\temp\\debugsms, assembles them into a\r\nCAB file for exfiltration, and then cleans up the folders from the system. The file also enables Windows Remote\r\nManagement and sets up an HTTP listener, indicating the attacker might take advantage of the internet-facing nature of\r\nan Exchange Server and use this method for later access if other tools are removed.\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 3 of 18\n\nFigure 3. xx.bat actions\r\nThe xx.bat file has been run on many more systems than have been ransomed by the DoejoCrypt attacker, meaning that,\r\nwhile not all systems have moved to the ransom stage, the attacker has gained access to multiple credentials. On systems\r\nwhere the attacker moved to the ransom stage, we saw reconnaissance commands being run via the same web shell that\r\ndopped the xx.bat file (in this instance, a version of Chopper):\r\nFigure 4. DoejoCrypt recon command\r\nAfter these commands are completed, the web shell drops a new payload to C:\\Windows\\Help which, like in many\r\nhuman-operated ransomware campaigns, leads to the attack framework Cobalt Strike. In observed instances, the\r\ndownloaded payload is shellcode with the file name new443.exe or Direct_Load.exe. When run, this payload injects\r\nitself into notepad.exe and reaches out to a C2 to download Cobalt Strike shellcode.\r\nFigure 5. DoejoCrypt ransomware attack chain\r\nDuring the hands-on-keyboard stage of the attack, a new payload is downloaded to C:\\Windows\\Help with names like\r\ns1.exe and s2.exe. This payload is the DoejoCrypt ransomware, which uses a .CRYPT extension for the newly encrypted\r\nfiles and a very basic readme.txt ransom note. In some instances, the time between xx.bat being dropped and a\r\nransomware payload running was under half an hour.\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 4 of 18\n\nFigure 6. DoejoCrypt ransom note\r\nWhile the DoejoCrypt payload is the most visible outcome of the attackers’ actions, the access to credentials they have\r\ngained could serve them for future campaigns if organizations do not reset credentials on compromised systems. An\r\nadditional overlapping activity observed on systems where xx.bat was present and the attackers were able to get Domain\r\nAdministrator rights was the running of scripts to snapshot Active Directory with ntdsutil—an action that, if executed\r\nsuccessfully, could give the attackers access to all the passwords in Active Directory from a single compromised system.\r\nLemon Duck botnet\r\nCryptocurrency miners were some of the first payloads we observed being dropped by attackers from the post-exploit\r\nweb shells. In the first few days after the security updates were released, we observed multiple cryptocurrency miner\r\ncampaigns, which had been previously targeting SharePoint servers, add Exchange Server exploitation to their\r\nrepertoire. Most of these coin miners were variations on XMRig miners, and many arrived via a multi-featured implant\r\nwith the capability to download new payloads or even move laterally.\r\nLemon Duck, a known cryptocurrency botnet named for a variable in its code, dove into the Exchange exploit action,\r\nadopting different exploit styles and choosing to use a fileless/web shell-less option of direct PowerShell commands\r\nfrom w3wp (the IIS worker process) for some attacks. While still maintaining their normal email-based campaigns, the\r\nLemon Duck operators compromised numerous Exchange servers and moved in the direction of being more of a\r\nmalware loader than a simple miner.\r\nUsing a form of the attack that allows direct execution of commands versus dropping a web shell, the Lemon Duck\r\noperators ran standard Invoke Expression commands to download a payload. Having used the same C2 and download\r\nservers for some time, the operators applied a varied degree of obfuscation to their commands on execution.\r\nFig 7. Example executions of Lemon Duck payload downloads\r\nThe Lemon Duck payload is an encoded and obfuscated PowerShell script. It first removes various security products\r\nfrom the system, then creates scheduled tasks and WMI Event subscription for persistence. A second script is\r\ndownloaded to attempt to evade Microsoft Defender Antivirus, abusing their administrative access to run the Set-MPPreference command to disable real-time monitoring (a tactic that Microsoft Defender Tamper protection blocks) and\r\nadd scanning exclusions for the C:\\ drive and the PowerShell process.\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 5 of 18\n\nFigure 8. Lemon Duck payloads\r\nOne randomly named scheduled task connects to a C2 every hour to download a new payload, which includes various\r\nlateral movement and credential theft tools. The operators were seen to download RATs and information stealers,\r\nincluding Ramnit payloads.\r\nFigure 9. Lemon Duck post-exploitation activities\r\nIn some instances, the operators took advantage of having compromised mail servers to access mailboxes and send\r\nemails containing the Lemon Duck payload using various colorful email subjects.\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 6 of 18\n\nFigure 10. Email subjects of possibly malicious emails\r\nFigure 11. Attachment variables\r\nIn one notable example, the Lemon Duck operators compromised a system that already had xx.bat and a web shell. After\r\nestablishing persistence on the system in a non-web shell method, the Lemon Duck operators were observed cleaning up\r\nother attackers’ presence on the system and mitigating the CVE-2021-26855 (SSRF) vulnerability using a legitimate\r\ncleanup script that they hosted on their own malicious server. This action prevents further exploitation of the server and\r\nremoves web shells, giving Lemon Duck exclusive access to the compromised server. This stresses the need to fully\r\ninvestigate systems that were exposed, even if they have been fully patched and mitigated, per traditional incident\r\nresponse process.\r\nPydomer ransomware\r\nWhile DoejoCrypt was a new ransomware payload, the access gained by attackers via the on-premises Exchange Server\r\nvulnerabilities will likely become part of the complex cybercriminal economy where additional ransomware operators\r\nand affiliates take advantage of it. The first existing ransomware family to capitalize on the vulnerabilities was Pydomer.\r\nThis ransomware family was previously seen using vulnerabilities in attacks, notably taking advantage of Pulse Secure\r\nVPN vulnerabilities, for which Pulse Secure has released security patches, to steal credentials and perform ransomware\r\nattacks.\r\nIn this campaign, the operators scanned and mass-compromised unpatched Exchange Servers to drop a web shell. They\r\nstarted later than some other attackers, with many compromises occurring between March 18 and March 20, a window\r\nwhen fewer unpatched systems were available. They then dropped a web shell, with a notable file name format:\r\n“Chack[Word][Country abbreviation]”:\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 7 of 18\n\nFigure 12. Example web shell names observed being used by the Pydomer attackers\r\nThese web shells were observed on around 1,500 systems, not all of which moved to the ransomware stage. The\r\nattackers then used their web shell to dump a test.bat batch file that performed a similar function in the attack chain to\r\nthe xx.bat of the DoejoCrypt operators and allowed them to perform a dump of the LSASS process.\r\nFigure 13. Pydomer post-exploitation activities\r\nThis access alone would be valuable to attackers for later attacks, similar to the credentials gained during their use of\r\nPulse Secure VPN vulnerabilities. The highly privileged credentials gained from an Exchange system are likely to\r\ncontain domain administrator accounts and service accounts with backup privileges, meaning these attackers could\r\nperform ransomware and exfiltration actions against the networks they compromised long after the Exchange Server is\r\npatched and even enter via different means.\r\nOn systems where the attackers did move to second-stage ransomware operations, they utilized a Python script compiled\r\nto an executable and the Python cryptography libraries to encrypt files. The attackers then executed a PowerShell script\r\nvia their web shell that acts as a downloader and distribution mechanism for the ransomware.\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 8 of 18\n\nFigure 14. PowerShell downloader and spreader used to get the Pydomer payload\r\nThe script fetches a payload from a site hosted on a domain generation algorithm (DGA) domain, and attempts to spread\r\nthe payload throughout the network, first attempting to spread the payload over WMI using Invoke-WMIMethod to\r\nattempt to connect to systems, and falling back to PowerShell remoting with Enter-PSSession if that fails. The script is\r\nrun within the context of the web shell, which in most instances is Local System, so this lateral movement strategy is\r\nunlikely to work except in organizations that are running highly insecure and unrecommended configurations like having\r\ncomputer objects in highly privileged groups.\r\nThe Pydomer ransomware is a Python script compiled to an executable and uses the Python cryptography libraries to\r\nencrypt files. The ransomware encrypts the files and appends a random extension, and then drops a ransom note named\r\ndecrypt_file.TxT.\r\nFigure 15. Pydomer ransom note\r\nInterestingly, the attackers seem to have deployed a non-encryption extortion strategy. Following well-known\r\nransomware groups like Maze and Egregor which leaked data for pay, the Pydomer hackers dropped an alternative\r\nreadme.txt onto systems without encrypting files. This option might have been semi-automated on their part or a side\r\neffect of a failure in their encryption process, as some of the systems they accessed were test systems that showed no\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 9 of 18\n\ndata exfiltration. The note should be taken seriously if encountered, as the attackers had full access to systems and were\r\nlikely able to exfiltrate data.\r\nFigure 16. Pydomer extortion readme.txt\r\nCredential theft, turf wars, and dogged persistence\r\nIf a server is not running in a least-privilege configuration, credential theft could provide a significant return on\r\ninvestment for an attacker beyond their initial access to email and data. Many organizations have backup agent software\r\nand scheduled tasks running on these systems with domain admin-level permissions. For these organizations, the\r\nattackers might be able to harvest highly privileged credentials without lateral movement, for example, using the COM\r\nservices DLL as a living-off-the-land binary to perform a dump of the LSASS process:\r\nFigure 17. Use of COM services DLL to dump LSASS process\r\nThe number of observed credential theft attacks, combined with high privilege of accounts often given to Exchange\r\nservers, means that these attacks could continue to impact organizations that don’t fully remediate after a compromise\r\neven after patches have been applied. While the observed ransomware attempts were small-scale or had errors, there is\r\nstill the possibility of more skillful groups utilizing credentials gained in these attacks for later attacks.\r\nAttackers also used their access to perform extensive reconnaissance using built-in Exchange commandlets and dsquery\r\nto exfiltrate information about network configurations, user information, and email assets.\r\nWhile Lemon Duck operators might have had the boldest method for removing other attackers from the systems they\r\ncompromised, they were not the only attacker to do so. Others were observed cleaning up .aspx and .bat files to remove\r\nother attackers, and even rebuilding the WMI database by deleting .mof files and restarting the service. As the window\r\non unpatched machines closes, attackers showed increased interest in maintaining the access to the systems they\r\nexploited. By utilizing “malwareless” persistence mechanisms like enabling RDP, installing Shadow IT tools, and adding\r\nnew local administrator accounts, the attackers are hoping to evade incident response efforts that might focus exclusively\r\non web shells, AV scans, and patching.\r\nDefending against exploits and post-compromise activities\r\nAttackers exploit the on-premises Exchange Server vulnerabilities in combination to bypass authentication and gain the\r\nability to write files and run malicious code. The best and most complete remediation for these vulnerabilities is to\r\nupdate to a supported Cumulative Update and to install all security updates. Comprehensive mitigation guidance can be\r\nfound here: https://aka.ms/ExchangeVulns.\r\nAs seen in the post-exploitation attacks discussed in this blog, the paths that attackers can take after successfully\r\nexploiting the vulnerabilities are varied and wide-ranging. If you have determined or have reason to suspect that these\r\nthreats are present on your network, here are immediate steps you can take:\r\nInvestigate exposed Exchange servers for compromise, regardless of their current patch status.\r\nLook for web shells via our guidance and run a full AV scan using the Exchange On-Premises Mitigation Tool.\r\nInvestigate Local Users and Groups, even non-administrative users for changes, and ensure all users require a\r\npassword for sign-in. New user account creations (represented by Event ID 4720) during the time the system was\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 10 of 18\n\nvulnerable might indicate a malicious user creation.\r\nReset and randomize local administrator passwords with a tool like LAPS if you are not already doing so.\r\nLook for changes to the RDP, firewall, WMI subscriptions, and Windows Remote Management (WinRM)\r\nconfiguration of the system that might have been configured by the attacker to allow persistence.\r\nLook for Event ID 1102 to determine if attackers cleared event logs, an activity that attackers perform with exe in\r\nan attempt to hide their tracks.\r\nLook for new persistence mechanisms such as unexpected services, scheduled tasks, and startup items.\r\nLook for Shadow IT tools that attackers might have installed for persistence, such as non-Microsoft RDP and\r\nremote access clients.\r\nCheck mailbox-level email forwarding settings (both ForwardingAddress and ForwardingSMTPAddress\r\nattributes), check mailbox inbox rules (which might be used to forward email externally), and check Exchange\r\nTransport rules that you might not recognize.\r\nWhile our response tools check for and remove known web shells and attack tools, performing a full investigation of\r\nthese systems is recommended. For comprehensive investigation and mitigation guidance and tools, see\r\nhttps://aka.ms/exchange-customer-guidance.\r\nAdditionally, here are best practices for building credential hygiene and practicing the principle of least privilege:\r\nFollow guidance to run Exchange in least-privilege configuration: https://adsecurity.org/?p=4119.\r\nEnsure service accounts and scheduled tasks run with the least privileges they need. Avoid widely privileged\r\ngroups like domain admins and backup operators and prefer accounts with access to just the systems they need.\r\nRandomize local administrator passwords to prevent lateral movement with tools like LAPS.\r\nEnsure administrators practice good administration habits like Privileged Admin Workstations.\r\nPrevent privileged accounts like domain admins from signing into member servers and workstations using Group\r\nPolicy to limit credential exposure and lateral movement.\r\nAppendix\r\nMicrosoft Defender for Endpoint detection details\r\nAntivirus                                                                                                                                   \r\nMicrosoft Defender Antivirus detects exploitation behavior with these detections:\r\nBehavior:Win32/Exmann\r\nBehavior:Win32/IISExchgSpawnEMS\r\nExploit:ASP/CVE-2021-27065\r\nExploit:Script/Exmann\r\nTrojan:Win32/IISExchgSpawnCMD\r\nBehavior:Win32/IISExchgDropWebshell\r\nWeb shells are detected as:\r\nBackdoor:JS/Webshell\r\nBackdoor:PHP/Chopper\r\nBackdoor:ASP/Chopper\r\nBackdoor:MSIL/Chopper\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 11 of 18\n\nTrojan:JS/Chopper\r\nTrojan:Win32/Chopper\r\nBehavior:Win32/WebShellTerminal\r\nRansomware payloads and associated files are detected as:\r\nTrojan:BAT/Wenam – xx.bat behaviors\r\nRansom:Win32/DoejoCrypt – DoejoCrypt ransomware\r\nTrojan:PowerShell/Redearps – PowerShell spreader in Pydomer attacks\r\nRansom:Win64/Pydomer – Pydomer ransomware\r\nLemon Duck malware is detected as:\r\nTrojan:PowerShell/LemonDuck\r\nTrojan:Win32/LemonDuck\r\nSome of the credential theft techniques highlighted in this report are detected as:\r\nBehavior:Win32/DumpLsass\r\nBehavior:Win32/RegistryExfil\r\nEndpoint detection and response (EDR)\r\nAlerts with the following titles in the security center can indicate threat activity on your network:\r\nSuspicious Exchange UM process creation\r\nSuspicious Exchange UM file creation\r\nSuspicious w3wp.exe activity in Exchange\r\nPossible exploitation of Exchange Server vulnerabilities\r\nPossible IIS web shell\r\nPossible web shell installation\r\nWeb shells associated with Exchange Server vulnerabilities\r\nNetwork traffic associated with Exchange Server exploitation\r\nAlerts with the following titles in the security center can indicate threat activity on your network specific to the\r\nDoejoCrypt and Pydomer ransomware campaign:\r\nDoejoCrypt ransomware\r\nPydomer ransomware\r\nPydomer download site\r\nAlerts with the following titles in the security center can indicate threat activity on your network specific to the Lemon\r\nDuck botnet:\r\nLemonDuck Malware\r\nLemonDuck botnet C2 domain activity\r\nThe following behavioral alerts might also indicate threat activity associated with this threat:\r\nPossible web shell installation\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 12 of 18\n\nA suspicious web script was created\r\nSuspicious processes indicative of a web shell\r\nSuspicious file attribute change\r\nSuspicious PowerShell command line\r\nPossible IIS Web Shell\r\nProcess memory dump\r\nA malicious PowerShell Cmdlet was invoked on the machine\r\nWDigest configuration change\r\nSensitive information lookup\r\nSuspicious registry export\r\nAdvanced hunting\r\nTo locate possible exploitation activities in Microsoft Defender for Endpoint, run the following queries.\r\nProcesses run by the IIS worker process\r\nLook for processes executed by the IIS worker process\r\n// Broadly search for processes executed by the IIS worker process. Further investigation should be\r\nperformed on any devices where the created process is indicative of reconnaissance\r\nDeviceProcessEvents\r\n| where InitiatingProcessFileName == 'w3wp.exe'\r\n| where InitiatingProcessCommandLine contains \"MSExchange\"\r\n| where FileName !in~\r\n(\"csc.exe\",\"cvtres.exe\",\"conhost.exe\",\"OleConverter.exe\",\"wermgr.exe\",\"WerFault.exe\",\"TranscodingService.exe\")\r\n| project FileName, ProcessCommandLine, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nSearch for PowerShell spawned from the IIS worker process, observed most frequently in Lemon Duck with Base64\r\nencoding to obfuscate C2 domains\r\nDeviceProcessEvents\r\n| where FileName =~ \"powershell.exe\"\r\n| where InitiatingProcessFileName =~ \"w3wp.exe\"\r\n| where InitiatingProcessCommandLine contains \"MSExchange\"\r\n| project ProcessCommandLine, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nTampering\r\nSearch for Lemon Duck tampering with Microsoft Defender Antivirus\r\nDeviceProcessEvents\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 13 of 18\n\n| where InitiatingProcessCommandLine has_all (\"Set-MpPreference\", \"DisableRealtimeMonitoring\", \"Add-MpPreference\", \"ExclusionProcess\")\r\n| project ProcessCommandLine, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nBatch script actions\r\nSearch for batch scripts performing credential theft, as observed in DoejoCrypt infections\r\nDeviceProcessEvents\r\n| where InitiatingProcessFileName == \"cmd.exe\"\r\n| where InitiatingProcessCommandLine has \".bat\" and InitiatingProcessCommandLine has @\"C:\\Windows\\Temp\"\r\n| where ProcessCommandLine has \"reg save\"\r\n| project ProcessCommandLine, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nLook for evidence of batch script execution that leads to credential dumping\r\n// Search for batch script execution, leading to credential dumping using rundll32 and the COM Services\r\nDLL, dsquery, and makecab use\r\nDeviceProcessEvents\r\n| where InitiatingProcessFileName =~ \"cmd.exe\"\r\n| where InitiatingProcessCommandLine has \".bat\" and InitiatingProcessCommandLine has\r\n@\"\\inetpub\\wwwroot\\aspnet_client\\\"\r\n| where InitiatingProcessParentFileName has \"w3wp\"\r\n| where FileName != \"conhost.exe\"\r\n| project FileName, ProcessCommandLine, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nSuspicious files dropped under an aspnet_client folder\r\nLook for dropped suspicious files like web shells and other components\r\n// Search for suspicious files, including but not limited to batch scripts and web shells, dropped under\r\nthe file path C:\\inetpub\\wwwroot\\aspnet_client\\\r\nDeviceFileEvents\r\n| where InitiatingProcessFileName == \"w3wp.exe\"\r\n| where FolderPath has \"\\\\aspnet_client\\\\\"\r\n| where InitiatingProcessCommandLine contains \"MSExchange\"\r\n| project FileName, FolderPath, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 14 of 18\n\nChecking for persistence on systems that have been suspected as compromised\r\nSearch for creations of new local accounts\r\nDeviceProcessEvents\r\n| where FileName == \"net.exe\"\r\n| where ProcessCommandLine has_all (\"user\", \"add\")\r\n| project ProcessCommandLine, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nSearch for installation events that were used to download ScreenConnect for persistence\r\nNote that this query may be noisy and is not necessarily indicative of malicious activity alone.\r\nDeviceProcessEvents\r\n| where FileName =~ \"msiexec.exe\"\r\n| where ProcessCommandLine has @\"C:\\Windows\\Temp\\\"\r\n| parse-where kind=regex flags=i ProcessCommandLine with @\"C:\\\\Windows\\\\Temp\\\\\" filename:string @\".msi\"\r\n| project filename, ProcessCommandLine, InitiatingProcessCommandLine, DeviceId, Timestamp\r\nHunting for credential theft\r\nSearch for logon events related to services and scheduled tasks on devices that may be Exchange servers. The results of\r\nthis query should be used to verify whether any of these users have privileged roles that might have enabled further\r\npersistence.\r\nletdevices=\r\nDeviceProcessEvents\r\n|whereInitiatingProcessFileName==\"w3wp.exe\"andInitiatingProcessCommandLinecontains\"MSExchange\"\r\n|distinctDeviceId;\r\n//\r\nDeviceLogonEvents\r\n|whereDeviceIdin(devices)\r\n|whereLogonTypein(\"Batch\",\"Service\")\r\n|projectAccountName,AccountDomain,LogonType,DeviceId,Timestamp\r\nSearch for WDigest registry key modification, which allows for the LSASS process to store plaintext passwords.\r\nDeviceRegistryEvents\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 15 of 18\n\n| where RegistryValueName == \"UseLogonCredential\"\r\n| where RegistryKey has \"WDigest\" and RegistryValueData == \"1\"\r\n| project PreviousRegistryValueData, RegistryValueData, RegistryKey, RegistryValueName,\r\nInitiatingProcessFileName, InitiatingProcessCommandLine, InitiatingProcessParentFileName, DeviceId,\r\nTimestamp\r\nSearch for the COM services DLL being executed by rundll32, which can be used to dump LSASS memory.\r\nDeviceProcessEvents\r\n| where InitiatingProcessCommandLine has_all (\"rundll32.exe\", \"comsvcs.dll\")\r\n| project FileName, ProcessCommandLine, InitiatingProcessFileName, InitiatingProcessCommandLine,\r\nInitiatingProcessParentFileName, DeviceId, Timestamp\r\nSearch for Security Account Manager (SAM) or SECURITY databases being saved, from which credentials can later be\r\nextracted.\r\nDeviceProcessEvents\r\n| where FileName == \"reg.exe\"\r\n| where ProcessCommandLine has \"save\" and ProcessCommandLine has_any (\"hklm\\\\security\", \"hklm\\\\sam\")\r\n| project InitiatingProcessFileName, InitiatingProcessCommandLine, FileName, ProcessCommandLine,\r\nInitiatingProcessParentFileName, DeviceId, Timestamp\r\nIndicators\r\nSelected indicators from attacks are included here, the threats may utilize files and network indicators not represented\r\nhere.\r\nFiles (SHA-256)\r\nThe following are file hashes for some of the web shells observed during attacks:\r\n201e4e9910dcdc8c4ffad84b60b328978db8848d265c0b9ba8473cf65dcd0c41\r\n2f0bc81c2ea269643cae307239124d1b6479847867b1adfe9ae712a1d5ef135e\r\n4edc7770464a14f54d17f36dc9d0fe854f68b346b27b35a6f5839adf1f13f8ea\r\n511df0e2df9bfa5521b588cc4bb5f8c5a321801b803394ebc493db1ef3c78fa1\r\n65149e036fff06026d80ac9ad4d156332822dc93142cf1a122b1841ec8de34b5\r\n811157f9c7003ba8d17b45eb3cf09bef2cecd2701cedb675274949296a6a183d\r\n8e90ed33c7ee82c0b64078ea36ec95f7420ba435c693b3b3dd728b494abf7dfc\r\na291305f181e24fe7194154b4cd355ccb039d5765709c80999e392efec69c90a\r\nb75f163ca9b9240bf4b37ad92bc7556b40a17e27c2b8ed5c8991385fe07d17d0\r\ndd29e8d47dde124c7d14e614e03ccaab3ecaa50e0a0bef985ed59e98928bc13d\r\nDoejoCrypt associated hashes:\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 16 of 18\n\n027119161d11ba87acc908a1d284b93a6bcafccc012e52ce390ecb9cd745bf27\r\n10bce0ff6597f347c3cca8363b7c81a8bff52d2ff81245cd1e66a6e11aeb25da\r\n2b9838da7edb0decd32b086e47a31e8f5733b5981ad8247a2f9508e232589bff\r\n904fbea2cd68383f32c5bc630d2227601dc52f94790fe7a6a7b6d44bfd904ff3\r\nbf53b637683f9cbf92b0dd6c97742787adfbc12497811d458177fdeeae9ec748\r\ne044d9f2d0f1260c3f4a543a1e67f33fcac265be114a1b135fd575b860d2b8c6\r\nfdec933ca1dd1387d970eeea32ce5d1f87940dfb6a403ab5fc149813726cbd65\r\nfeb3e6d30ba573ba23f3bd1291ca173b7879706d1fe039c34d53a4fdcdf33ede\r\nLemon Duck associated hashes:\r\n0993cc228a74381773a3bb0aa36a736f5c41075fa3201bdef4215a8704e582fc\r\n3df23c003d62c35bd6da90df12826c1d3fdd94029bf52449ba3d89920110d5ec\r\n4f0b9c0482595eee6d9ece0705867b2aae9e4ff68210f32b7425caca763723b9\r\n56101ab0881a6a34513a949afb5a204cad06fd1034f37d6791f3ab31486ba56c\r\n69ce57932c3be3374e8843602df1c93e1af622fc53f3f1d9b0a75b66230a1e2e\r\n737752588f32e4c1d8d20231d7ec553a1bd4a0a090b06b2a1835efa08f9707c4\r\n893ddf0de722f345b675fd1ade93ee1de6f1cad034004f9165a696a4a4758c3e\r\n9cf63310788e97f6e08598309cbbf19960162123e344df017b066ca8fcbed719\r\n9f2fe33b1c7230ec583d7f6ad3135abcc41b5330fa5b468b1c998380d20916cd\r\na70931ebb1ce4f4e7d331141ad9eba8f16f98da1b079021eeba875aff4aeaa85\r\nd8b5eaae03098bead91ff620656b9cfc569e5ac1befd0f55aee4cdb39e832b09\r\ndb093418921aae00187ae5dc6ed141c83614e6a4ec33b7bd5262b7be0e9df2cd\r\ndc612f5c0b115b5a13bdb9e86f89c5bfe232e5eb76a07c3c0a6d949f80af89fd\r\nf517526fc57eb33edb832920b1678d52ad1c5cf9c707859551fe065727587501\r\nf8d388f502403f63a95c9879c806e6799efff609001701eed409a8d33e55da2f\r\nfbeefca700f84373509fd729579ad7ea0dabdfe25848f44b2fbf61bf7f909df0\r\nPydomer associated hashes:\r\n7e07b6addf2f0d26eb17f4a1be1cba11ca8779b0677cedc30dbebef77ccba382\r\n866b1f5c5edd9f01c5ba84d02e94ae7c1f9b2196af380eed1917e8fc21acbbdc\r\n910fbfa8ef4ad7183c1b5bdd3c9fd1380e617ca0042b428873c48f71ddc857db\r\na387c3c5776ee1b61018eeb3408fa7fa7490915146078d65b95621315e8b4287\r\nb9dbdf11da3630f464b8daace88e11c374a642e5082850e9f10a1b09d69ff04f\r\nc25a5c14269c990c94a4a20443c4eb266318200e4d7927c163e0eaec4ede780a\r\nc4aa94c73a50b2deca0401f97e4202337e522be3df629b3ef91e706488b64908\r\nNetwork indicators\r\nDomains abused by Lemon Duck:\r\ndown[.]sqlnetcat[.]com\r\nt[.]sqlnetcat[.]com\r\nt[.]netcatkit[.]com\r\nPydomer DGA network indicators:\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 17 of 18\n\nuiiuui[.]com/search/*\r\nyuuuuu43[.]com/vpn-service/*\r\nyuuuuu44[.]com/vpn-service/*\r\nyuuuuu46[.]com/search/*\r\nSource: https://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nhttps://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/\r\nPage 18 of 18",
	"extraction_quality": 1,
	"language": "EN",
	"sources": [
		"Malpedia"
	],
	"origins": [
		"web"
	],
	"references": [
		"https://www.microsoft.com/security/blog/2021/03/25/analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities/"
	],
	"report_names": [
		"analyzing-attacks-taking-advantage-of-the-exchange-server-vulnerabilities"
	],
	"threat_actors": [
		{
			"id": "7c969685-459b-4c93-a788-74108eab6f47",
			"created_at": "2023-01-06T13:46:39.189751Z",
			"updated_at": "2026-04-12T02:00:03.320806Z",
			"deleted_at": null,
			"main_name": "HAFNIUM",
			"aliases": [
				"ATK233",
				"G0125",
				"Operation Exchange Marauder",
				"Red Dev 13",
				"Silk Typhoon",
				"MURKY PANDA"
			],
			"source_name": "MISPGALAXY:HAFNIUM",
			"tools": [],
			"source_id": "MISPGALAXY",
			"reports": null
		},
		{
			"id": "2704d770-43b4-4bc4-8a5a-05df87416848",
			"created_at": "2022-10-25T15:50:23.306305Z",
			"updated_at": "2026-04-12T02:00:04.412723Z",
			"deleted_at": null,
			"main_name": "HAFNIUM",
			"aliases": [
				"HAFNIUM",
				"Operation Exchange Marauder",
				"Silk Typhoon"
			],
			"source_name": "MITRE:HAFNIUM",
			"tools": [
				"Tarrask",
				"ASPXSpy",
				"Impacket",
				"PsExec",
				"China Chopper"
			],
			"source_id": "MITRE",
			"reports": null
		},
		{
			"id": "529c1ae9-4579-4245-86a6-20f4563a695d",
			"created_at": "2022-10-25T16:07:23.702006Z",
			"updated_at": "2026-04-12T02:00:04.635543Z",
			"deleted_at": null,
			"main_name": "Hafnium",
			"aliases": [
				"G0125",
				"Murky Panda",
				"Red Dev 13",
				"Silk Typhoon"
			],
			"source_name": "ETDA:Hafnium",
			"tools": [],
			"source_id": "ETDA",
			"reports": null
		}
	],
	"ts_created_at": 1775791291,
	"ts_updated_at": 1775960508,
	"ts_creation_date": 0,
	"ts_modification_date": 0,
	"files": {
		"pdf": "https://archive.orkl.eu/97cc2b087643f7855785b03622bd2944d89404f2.pdf",
		"text": "https://archive.orkl.eu/97cc2b087643f7855785b03622bd2944d89404f2.txt",
		"img": "https://archive.orkl.eu/97cc2b087643f7855785b03622bd2944d89404f2.jpg"
	}
}