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HAFNIUM group was identified by Microsoft as exploiting 4 Microsoft Exchange CVEs in the wild - CVE-2021-26855, CVE-2021-26857, CVE-2021-26858 and CVE-2021-27065.

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Endpoint, Network_Traffic
  • Last Updated: 2021-03-03
  • Author: Michael Haag, Splunk
  • ID: beae2ab0-7c3f-11eb-8b63-acde48001122


On Tuesday, March 2, 2021, Microsoft released a set of security patches for its mail server, Microsoft Exchange. These patches respond to a group of vulnerabilities known to impact Exchange 2013, 2016, and 2019. It is important to note that an Exchange 2010 security update has also been issued, though the CVEs do not reference that version as being vulnerable.
While the CVEs do not shed much light on the specifics of the vulnerabilities or exploits, the first vulnerability (CVE-2021-26855) has a remote network attack vector that allows the attacker, a group Microsoft named HAFNIUM, to authenticate as the Exchange server. Three additional vulnerabilities (CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065) were also identified as part of this activity. When chained together along with CVE-2021-26855 for initial access, the attacker would have complete control over the Exchange server. This includes the ability to run code as SYSTEM and write to any path on the server.
The following Splunk detections assist with identifying the HAFNIUM groups tradecraft and methodology.


Name Technique Type
Any Powershell DownloadString PowerShell TTP
Detect Exchange Web Shell Web Shell TTP
Detect New Local Admin account Local Account TTP
Detect PsExec With accepteula Flag SMB/Windows Admin Shares TTP
Detect Renamed PSExec Service Execution Hunting
Dump LSASS via comsvcs DLL LSASS Memory TTP
Dump LSASS via procdump LSASS Memory TTP
Email servers sending high volume traffic to hosts Remote Email Collection Anomaly
Malicious PowerShell Process - Connect To Internet With Hidden Window PowerShell Hunting
Malicious PowerShell Process - Execution Policy Bypass PowerShell TTP
Nishang PowershellTCPOneLine PowerShell TTP
Ntdsutil Export NTDS NTDS TTP
Set Default PowerShell Execution Policy To Unrestricted or Bypass PowerShell TTP
Unified Messaging Service Spawning a Process Exploit Public-Facing Application TTP
W3WP Spawning Shell Web Shell TTP


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