CVE-2024-27443: Synacor Zimbra Collaboration Suite XSS in CalendarInvite

CVE-2024-27443 · Severity: critical · CVSS 6.1 · Exploited in the wild · Published 2025-05-19

Zimbra Collaboration Suite is a widely used enterprise email and collaboration platform. A security flaw in its classic webmail interface allows an attacker to execute malicious code in a user's browser simply by sending them a specially crafted calendar invitation. This could allow an attacker to steal session information, access sensitive emails, or perform actions on behalf of the victim. This vulnerability has been observed being used in active attacks.

Technologies: Synacor Zimbra Collaboration Suite, Synacor Zimbra Collaboration Suite (ZCS). Vendors: Synacor.

Quick answers

Is CVE-2024-27443 exploited in the wild?
Yes. CVE-2024-27443 is known to be exploited in the wild, first recorded on 19 May 2025. Treat it as urgent.
How severe is CVE-2024-27443?
Critical severity, with a CVSS score of 6.1, published 19 May 2025.
Which products and versions are affected?
Synacor Zimbra Collaboration Suite 9.0.0 before P39, 10.0.0 before 10.0.7.
Is there a fix for CVE-2024-27443?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2024-27443 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2024-27443?
Check whether you run Synacor Zimbra Collaboration Suite or Synacor Zimbra Collaboration Suite (ZCS) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A stored Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface (CWE-79). The issue stems from improper input validation of calendar headers in incoming email messages. An unauthenticated remote attacker can exploit this by sending an email with a malicious payload embedded in the calendar header; when a victim views the message, the payload executes in the context of their session. This vulnerability has been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. Patches are available in Zimbra 9.0.0 Patch 39 and Zimbra 10.0.7.

Affected products

  • Synacor Zimbra Collaboration Suite (ZCS) 9.0.0 before P39, 10.0.0 before 10.0.7

Timeline

  • 2024-03-17: advisory: Initial CVSS scoring and CWE assignment
  • 2025-05-19: kev added: Added to CISA Known Exploited Vulnerabilities catalog
  • 2025-05-19: exploited: Confirmed active exploitation in the wild

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