CVE-2024-27443
Published 2024-08-12 · Updated 2026-06-17 · Source cve@mitre.org
Summary
CVE-2024-27443 is a medium-severity (CVSS 6.1) vulnerability in Synacor Zimbra Collaboration Suite (ZCS). CISA added it to the Known Exploited Vulnerabilities catalog on May 19, 2025, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by June 9, 2025. CISA does not currently list it as used in ransomware campaigns. Synacor has 19 vulnerabilities in the KEV catalog, 6 of them linked to ransomware.
All 19 known-exploited Synacor vulnerabilities →Description
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0. A Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface, because of improper input validation in the handling of the calendar header. An attacker can exploit this via an email message containing a crafted calendar header with an embedded XSS payload. When a victim views this message in the Zimbra webmail classic interface, the payload is executed in the context of the victim's session, potentially leading to execution of arbitrary JavaScript code.
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CISA Known-Exploited Vulnerability
Product: Synacor — Zimbra Collaboration Suite (ZCS)
Name: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
Date added: 2025-05-19 · Due: 2025-06-09
Required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.