Microsoft has detected multiple 0-day exploits being used to attack on-premises versions of Microsoft Exchange Server in limited and targeted attacks. In the attacks observed, the threat actor used these vulnerabilities to access on-premises Exchange servers which enabled access to email accounts, and allowed installation of additional malware to facilitate long-term access to victim environments. Microsoft Threat Intelligence Center (MSTIC) attributes this campaign with high confidence to HAFNIUM a group assessed to be state-sponsored and operating out of China, based on observed victimology, tactics and procedures.
The vulnerabilities recently being exploited were CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065. We strongly urge customers to update on-premises systems immediately. Exchange Online is not affected.
We are sharing this information with customers and the security community to emphasize the critical nature of these vulnerabilities and the importance of patching all affected systems immediately to protect against these exploits and prevent future abuse across the ecosystem.
Who is HAFNIUM?
HAFNIUM primarily targets entities in the United States across a number of industry sectors, including infectious disease researchers, law firms, higher education institutions, defense contractors, policy think tanks, and NGOs.
HAFNIUM has previously compromised victims by exploiting vulnerabilities in internet-facing servers, and has used legitimate open-source frameworks, like Covenant, for command and control. Once they’ve gained access to a victim network, HAFNIUM typically exfiltrates data to file sharing sites like Mega.
In campaigns unrelated to these vulnerabilities, Microsoft has observed HAFNIUM interacting with victim Office 365 tenants. While they are often unsuccessful in compromising customer accounts, this reconnaissance activity helps the adversary identify more details about their targets’ environments.
HAFNIUM operates primarily from leased virtual private servers (VPS) in the United States.
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