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Attacker Value
Very High
Microsoft disclosed four actively exploited zero-day vulnerabilities being used to attack on-premises versions of Microsoft Exchange Server. The vulnerabilities identified are CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065, all of which affect Microsoft Exchange Server. Exchange Online is not affected. 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.
18
Attacker Value
Very High

CVE-2021-26855

Disclosure Date: March 03, 2021 (last updated December 30, 2023)
Microsoft Exchange Server Remote Code Execution Vulnerability
Attacker Value
Very High

CVE-2021-26857

Disclosure Date: March 03, 2021 (last updated July 26, 2024)
Microsoft Exchange Server Remote Code Execution Vulnerability
Attacker Value
Very High

CVE-2021-27065

Disclosure Date: March 03, 2021 (last updated July 26, 2024)
Microsoft Exchange Server Remote Code Execution Vulnerability