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Poland's CERT Warns of Active Exploitation of Critical Zimbra Collaboration Suite Flaw
CERT Polska confirms active exploitation of critical unauthenticated RCE CVE-2026-73570 in Zimbra Collaboration Suite, patched July 20.
CERT Polska confirmed threat actors are actively exploiting CVE-2026-73570, an unauthenticated OS command injection in Zimbra Collaboration Suite allowing arbitrary shell commands as the zimbra user. Exploitation requires the SNMP trap service via snmp_notify with swatchdog running, which is enabled by default; Shadowserver tracks over 12,100 internet-exposed Zimbra servers. Zimbra fixed the flaw in version 10.1.20 on July 20, 2026, 28 days before exploitation was confirmed. Historical Zimbra targeting includes Winter Vivern, APT29, and APT28 campaigns.
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Attackers Exploit Zimbra SNMP Flaw for Unauthenticated Remote Code Execution
CERT Polska and CISA report active exploitation of Zimbra RCE CVE-2026-73570, with 267 instances compromised per Shadowserver.
CVE-2026-73570 (CVSS 8.9) enables unauthenticated command injection and remote code execution in Zimbra Collaboration before 10.1.20 when the optional zimbra-snmp package is installed and SNMP notifications are enabled, via crafted SMTP requests. CISA added the flaw to its KEV catalog on August 21, 2026, with a federal patch deadline of August 24. The Shadowserver Foundation counted 267 compromised instances as of August 24, 2026, led by the US (46), Sweden (21), France (20) and Germany (17). Separately, Russia-linked Laundry Bear has weaponized Zimbra stored XSS CVE-2025-66376 against Western government and commercial mail servers since at least July 2025, delivering the ZimReaper payload.
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U.S. CISA adds Zimbra Collaboration Suite (ZCS) flaw to its Known Exploited Vulnerabilities catalog
CISA added actively exploited Zimbra flaw CVE-2026-73570 (unauthenticated OS command injection RCE) to its KEV catalog, setting an August 24, 2026 federal patch deadline.
CISA added CVE-2026-73570, an unauthenticated OS command injection flaw in Zimbra Collaboration Suite, to its Known Exploited Vulnerabilities catalog after CERT Polska confirmed active exploitation. The flaw lets attackers execute shell commands as the zimbra user via the snmp_notify parameter when the SNMP trap service is enabled and the default swatchdog service is running. Zimbra patched the issue in version 10.1.20 released July 20, 2026, 28 days before exploitation was confirmed. Under BOD 22-01, federal civilian agencies must patch by August 24, 2026.
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Unpatched Zimbra servers are falling to CVE-2026-73570 attacks
Attackers are exploiting unpatched Zimbra servers via CVE-2026-73570; 274 instances compromised, and CISA added the flaw to its KEV catalog.
The Shadowserver Foundation counted at least 274 compromised internet-facing Zimbra Collaboration Suite instances exploited through CVE-2026-73570, up from 155 on August 20. The unauthenticated code injection flaw affects servers with the optional zimbra-snmp package and SNMP notifications enabled, allowing arbitrary OS command execution via crafted SMTP requests. Synacor patched the issue in ZCS v10.1.20 on July 20, 2026, and at least 8,200 instances remain unpatched. CISA added the flaw to its Known Exploited Vulnerabilities catalog and gave US federal civilian agencies three days to remediate and check for compromise.
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Critical XSS vulnerability in Zimbra exploited in the wild (CVE-2023-34192)
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