Zimbra Zero-Day Abused via iCalendar (.ICS) Files — What Administrators Need to Know

NewsBy Cristian SantanaOctober 5, 2025

Zimbra Zero-Day Abused via iCalendar (.ICS) Files — What Administrators Need to Know Summary of the incident Researchers monitoring for unusually large .ICS calendar attachments discovered that a flaw in Zimbra Collaboration Suite (ZCS) was actively exploited as a zero-day earlier this year. The attackers used iCalendar files to trigger the vulnerability, enabling compromise of…

Zimbra Zero‑Day Abused via Malicious iCalendar (.ICS) Attachments

NewsBy Cristian SantanaOctober 5, 2025

Zimbra Zero‑Day Abused via Malicious iCalendar (.ICS) Attachments Summary of the discovery Researchers monitoring for larger .ICS calendar attachments found that a flaw in Zimbra Collaboration Suite (ZCS) was used in zero-day attacks at the beginning of the year. That finding indicates attackers leveraged the iCalendar format — commonly used for meeting invites and calendar…