Zimbra Collaboration email software fell victim to real-world attacks orchestrated by four distinct hacker groups, exploiting a zero-day flaw tracked as CVE-2023-37580. Google Threat Analysis Group (TAG) disclosed that most exploitation occurred after the initial fix became public on GitHub, emphasizing the urgency of prompt patching.
Furthermore, the flaw, a reflected cross-site scripting (XSS) vulnerability impacting versions before 8.8.15 Patch 41, allowed attackers to execute malicious scripts by tricking users into clicking on specially crafted URLs, reflecting the attack back to the user.
Discovered by Google TAG researcher Clément Lecigne, the exploits unfolded in multiple campaign waves starting June 29, 2023, with three campaigns observed before Zimbra’s advisory and the fourth detected a month after the patch release. The first campaign targeted a Greek government organization, deploying exploit URLs that delivered email-stealing malware previously seen in the EmailThief cyber espionage operation.
Additionally, the second group, identified as Winter Vivern, focused on government organizations in Moldova and Tunisia immediately after the patch release on July 5, linking them to prior exploits in Zimbra Collaboration and Roundcube. A third, unidentified group targeted a government organization in Vietnam, employing the bug to phish credentials before the patch release on July 25.
The fourth campaign, occurring on August 25, targeted a government organization in Pakistan, resulting in the exfiltration of Zimbra authentication tokens to the remote domain “ntcpk[.]org”.
Google TAG highlighted a concerning pattern of threat actors exploiting XSS vulnerabilities in mail servers, underscoring the need for comprehensive audits of such applications. The discovery of four campaigns exploiting CVE-2023-37580, especially three after the bug became public, underscores the critical importance of organizations promptly applying fixes to secure their mail servers against opportunistic attacks.