A critical vulnerability in Zimbra Collaboration Suite could allow attackers to execute malicious code in user sessions simply by sending a crafted email, posing a direct threat to healthcare organizations that depend on the platform for secure communications.
The flaw, tracked as CVE-2025-27915, allows an unauthenticated attacker to inject and execute arbitrary code within the context of a victims Zimbra webmail session. The vulnerability is triggered when a user opens a specially crafted email message, requiring no additional interaction beyond viewing the email.
Zimbra is widely deployed in healthcare environments, hospitals, academic medical centers, and health systems use it as their primary email and collaboration platform. An attacker exploiting CVE-2025-27915 could gain access to sensitive email communications, including patient referrals, lab results, and administrative credentials, as well as pivot to internal systems connected to the Zimbra infrastructure.
The vulnerability chains together two older issues: CVE-2023-37580, a reflected XSS flaw in Zimbra ZCS, and CVE-2024-27443, a privilege escalation bug. Researchers demonstrated that combining these weaknesses enables a remote attacker to bypass authentication controls and execute arbitrary JavaScript in the context of any users session, effectively bypassing email security controls.
Healthcare organizations using Zimbra should immediately apply the latest security patches, restrict access to the Zimbra web interface, and monitor for signs of exploitation. Given the low complexity of the attack chain and the fact that it requires only a single email to trigger, this vulnerability should be treated as a critical priority for patching.
