Attackers Exploit Zimbra Flaw to Deploy Web Shells and Harvest Authentication Secrets

Attackers Exploit Zimbra Flaw to Deploy Web Shells and Harvest Authentication Secrets Ravie LakshmananSep 30, 2026Vulnerability / Email Security Threat actors have weaponized a now-patched security flaw in Zimbra Collaboration Suite (ZCS) to deploy web shells and access mailbox data, according to findings from the Microsoft Security Research team. The attack exploits CVE-2026-73570 (CVSS score: 8.9), an unauthenticated operating system command injection flaw that can lead to remote code execution when Simple Network Management Protocol (SNMP) notifications are enabled and the optional zimbra-snmp package is installed. Exploitation of CVE-2026-73570 can be triggered by a specially crafted SMTP request (i.e., email against exposed Zimbra servers without requiring authentication or user interaction. The vulnerability was patched by Zimbra in July 2026 with…