A now-patched security flaw impacting Zimbra Collaboration (ZCS) has come under active exploitation in the wild, according to the Polish Computer Emergency Response Team (CERT Polska).
The vulnerability in question is CVE-2026-73570 (CVSS score: 8.9), which refers to a case of command injection that can lead to remote code execution.
“A remote code execution vulnerability exists in Zimbra Collaboration (ZCS) before 10.1.20 when the optional zimbra-snmp package is installed, and SNMP notifications are enabled,” according to a description of the flaw in the NIST National Vulnerability Database (NVD).
“Due to improper sanitization of untrusted input during SNMP notification processing, an unauthenticated attacker can send specially crafted SMTP requests that may result in execution of arbitrary operating system commands as the Zimbra user.”
The security issue was patched by Zimbra last month with the release of version 10.1.20.
In a bulletin issued earlier this week, CERT Polska alerted of active exploitation efforts targeting the flaw, urging users to check the “/var/log/zimbra.log” file for suspicious Zimbra service restarts, as well as for files created in the below directories within the last 30 days –
- /opt/zimbra/jetty/webapps/
- /opt/zimbra/jetty_base/webapps/
- /tmp/
Vulnerabilities in Zimbra have been frequently targeted by threat actors. Last month, the U.S. government disclosed details of a phishing campaign orchestrated by a Russia-linked adversary called Laundry Bear (aka CL-STA-1114, TA488, UNK_PitStop, and Void Blizzard) that involved targeting Zimbra mail servers belonging to Western government and commercial organizations since at least July 2025.
The campaign was found to have weaponized CVE-2025-66376, a stored cross-site scripting vulnerability in Zimbra’s Classic UI, to deliver a malicious JavaScript payload dubbed ZimReaper to harvest email communications and other sensitive data.
