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UNC2639 is a Mandiant temporary cluster designation for activity associated with early 2021 exploitation of on-premises Microsoft Exchange Server vulnerabilities in the ProxyLogon attack chain. It was tracked alongside related clusters UNC2640 and UNC2643 during investigations into widespread compromise involving Exchange Server 2013, 2016, and 2019. The activity aligned with exploitation that Microsoft linked to the China-linked state-sponsored actor HAFNIUM, but UNC2639 itself is a preliminary cluster rather than a fully established intrusion set with a distinct long-term identity. Observed tradecraft included exploitation of Exchange vulnerabilities for remote code execution, deployment of web shells for persistent access, and follow-on post-compromise activity. Malicious file creation was observed under highly privileged contexts and through Exchange-related processes including the Unified Messaging worker process and the IIS worker process. Follow-on behavior included reconnaissance for endpoint security products, credential gathering, lateral movement, and broader system compromise. Web shells associated with this activity included logic to detect common endpoint security tools, indicating deliberate defense-evasion and post-exploitation objectives. Victimology associated with the broader clustered activity included organizations in the United States such as retailers, local governments, a university, and an engineering firm. Additional possible related victimology included a Southeast Asian government and a Central Asian telecommunications entity. The broader exploitation wave affected organizations globally and was primarily associated with espionage-oriented targeting in the early phase.
Mallory correlates actor tradecraft and target patterns against your stack, your sector, and your geography. See overlap before they land.
Who, where, and (when attributed) which flag flies behind the operation. Pulled from open-source reporting and Mallory's analyst review.
Sectors the actor has been observed targeting.
Geographies tied to known operations.
Attributed origin per open-source reporting.
4 distinct techniques observed across reporting, grouped by tactic. Hover any cell for the evidence excerpt; click through for MITRE's full description.
4 CVEs this actor has used in observed campaigns. 4 of them exploited in the wild.
CVE-2021-26855 (CVSS 9.1) is a server-side request forgery (SSRF) vulnerability in Exchange that allows the attacker to send arbitrary HTTP requests and authenticate as the Exchange server.
CVE-2021-26857 (CVSS 7.8) is an insecure deserialization vulnerability in the Unified Messaging service. Exploiting this vulnerability gives the threat actor the ability to run code as SYSTEM on the Exchange server.
CVE-2021-26858 (CVSS 7.8) is a post-authentication arbitrary file write vulnerability in Exchange. If the threat actor first authenticates with the Exchange server they could then use this vulnerability to write a file to any path on the server.
CVE-2021-27065 (CVSS 7.8) is a post-authentication arbitrary file write vulnerability in Exchange. If the threat actor first authenticates with the Exchange server they could then use this vulnerability to write a file to any path on the server.
2 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Match sector + geo + tech-stack targeting against your real footprint.
Every observed MITRE ATT&CK technique, grouped by tactic.
Families this actor is known to deploy, with IOCs and behavior.
CVEs this actor has used in known campaigns.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Domains, IPs, and hashes tied to this actor, refreshed continuously.