Threat actors have already compromised over 270 Zimbra instances in remote code execution attacks targeting a high-severity Zimbra Collaboration Suite (ZCS) vulnerability.
The ZCS email and collaboration suite is used by hundreds of millions of people and organizations, including thousands of businesses and hundreds of government agencies worldwide.
Synacor patched the security flaw (tracked as CVE-2026-73570), which allows unauthenticated attackers to gain code execution remotely by exploiting a command injection weakness in the SNMP monitoring component when SNMP notifications are enabled, with the release of ZCS version 10.1.20 on July 20.
CERT Polska, the Polish Computer Emergency Response Team (CERT), first flagged the vulnerability as targeted in the wild last Monday, when it also warned security teams to check their logs for suspicious activity, including the Zimbra service restarting unexpectedly, and for files created in the /opt/zimbra/jetty/webapps/, /opt/zimbra/jetty_base/webapps/, and /tmp/ folders by user zimbra over the last 30 days.
The Cybersecurity and Infrastructure Security Agency (CISA) also added the flaw to its KEV catalog following CERT Polska's warning and ordered U.S. Federal Civilian Executive Branch (FCEB) agencies to patch their systems within three days, by August 24.
