{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/tags/cve-2021-26857/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[{"cvss":7.8,"id":"CVE-2021-26857"}],"_cs_exploited":true,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["Exchange Server"],"_cs_severities":["medium"],"_cs_tags":["exchange","initial-access","lateral-movement","cve-2021-26857","windows"],"_cs_type":"threat","_cs_vendors":["Microsoft"],"content_html":"\u003cp\u003eThis detection rule identifies suspicious processes spawned by the Microsoft Exchange Server Unified Messaging (UM) service, a behavior indicative of potential exploitation of CVE-2021-26857. The Unified Messaging service integrates voice messaging with email, providing users access to voicemails via their inbox. Attackers exploit vulnerabilities to execute unauthorized processes, potentially leading to system compromise. The rule flags unusual processes initiated by UM services, excluding known legitimate executables like \u003ccode\u003ewerfault.exe\u003c/code\u003e and legitimate \u003ccode\u003eUMWorkerProcess.exe\u003c/code\u003e paths, to detect potential exploitation attempts. This activity was initially observed in March 2021 during the Hafnium attacks targeting Exchange servers. Defenders should be aware of unusual processes being launched from the UM service, as this is not typical behavior.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAttacker exploits CVE-2021-26857 or a similar vulnerability in Microsoft Exchange Server.\u003c/li\u003e\n\u003cli\u003eSuccessful exploitation allows the attacker to execute arbitrary code on the Exchange Server.\u003c/li\u003e\n\u003cli\u003eThe attacker leverages the Unified Messaging service (\u003ccode\u003eUMService.exe\u003c/code\u003e or \u003ccode\u003eUMWorkerProcess.exe\u003c/code\u003e) as a vehicle to launch malicious processes.\u003c/li\u003e\n\u003cli\u003eA suspicious process (e.g., \u003ccode\u003ecmd.exe\u003c/code\u003e, \u003ccode\u003epowershell.exe\u003c/code\u003e, or other unauthorized executable) is spawned by the UM service.\u003c/li\u003e\n\u003cli\u003eThe malicious process executes commands to perform reconnaissance, establish persistence, or move laterally within the network.\u003c/li\u003e\n\u003cli\u003eThe attacker might attempt to dump credentials, install backdoors, or exfiltrate sensitive data.\u003c/li\u003e\n\u003cli\u003eThe attacker moves laterally to other systems using compromised credentials or other exploits.\u003c/li\u003e\n\u003cli\u003eThe ultimate objective is to gain complete control of the network, steal sensitive data, or deploy ransomware.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation of Exchange Server vulnerabilities and subsequent spawning of malicious processes can lead to complete compromise of the Exchange server and potentially the entire Active Directory domain. Attackers can gain access to sensitive emails, customer data, and internal documents. The initial wave of attacks exploiting CVE-2021-26857 impacted thousands of organizations globally. Successful attacks can result in data breaches, financial losses, and reputational damage.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eDeploy the Sigma rule \u0026quot;Microsoft Exchange Server UM Spawning Suspicious Processes\u0026quot; to detect unauthorized processes spawned by the UM service. Enable process creation logging on Windows servers (Sysmon or Windows Security Event Logs) to collect the necessary data for the rule to function.\u003c/li\u003e\n\u003cli\u003eReview and update the exclusion list in the Sigma rule to account for legitimate processes spawned by the UM service in your specific environment. This will help reduce false positives.\u003c/li\u003e\n\u003cli\u003eApply the latest security patches and updates to Microsoft Exchange Server to address CVE-2021-26857 and other known vulnerabilities.\u003c/li\u003e\n\u003cli\u003eMonitor the command-line arguments of processes spawned by the UM service for suspicious activity.\u003c/li\u003e\n\u003cli\u003eInvestigate any alerts generated by the Sigma rule to determine the scope of the compromise and take appropriate remediation steps.\u003c/li\u003e\n\u003cli\u003eRegularly review Exchange Server security logs for suspicious activity and indicators of compromise.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2024-01-09T14:22:00Z","date_published":"2024-01-09T14:22:00Z","id":"https://feed.craftedsignal.io/briefs/2024-01-exchange-um-spawn/","summary":"This rule detects suspicious processes spawned by the Microsoft Exchange Server Unified Messaging (UM) service, potentially indicating exploitation of CVE-2021-26857 and leading to unauthorized process execution and system compromise.","title":"Microsoft Exchange Server UM Spawning Suspicious Processes","url":"https://feed.craftedsignal.io/briefs/2024-01-exchange-um-spawn/"}],"language":"en","title":"CraftedSignal Threat Feed - Cve-2021-26857","version":"https://jsonfeed.org/version/1.1"}