Microsoft catches hackers exploiting Zimbra bug before disclosure

Attackers were poking at a critical Zimbra mail server bug weeks before it was publicly disclosed, and then moved on to steal credentials, raid mailboxes, and take deeper control of compromised systems. Microsoft Threat Intelligence said it tracked exploitation of CVE-2026-73570, an unauthenticated command injection vulnerability in Zimbra Collaboration Suite that gives attackers a potentially easy route into exposed mail servers. No stolen password or unfortunate employee clicking a dodgy link is required. An attacker can send a specially crafted email to a vulnerable internet-facing server and potentially run commands, though Redmond notes the flaw affects only servers running Zimbra's optional SNMP monitoring package with notifications enabled. Zimbra fixed the flaw in version 10.1.20 on July 20, but CVE-2026-73570 wasn't publicly disclosed until August 13. Between July 28 and August 7, Redmond spotted two different scanning tools probing the same part of Zimbra later used in attacks. …