CISA KEV · Known exploitedMedium

CVE-2024-27443

Synacor Zimbra Collaboration Suite (ZCS)

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: 6.1
EPSS: 23.6%
CISA KEV: Listed
Published: 2024.08.13

PRIORITY ASSESSMENT

Immediate review

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog.

Known exploitationConfirmed by CISA KEV

Exploit probability23.6%

Technical severityCVSS 6.1

Vulnerability overview

Affected product and versions

Product: Synacor Zimbra Collaboration Suite (ZCS)
Affected versions: >= 10.0.0 < 10.0.7, 9.0.0
Fixed versions: 10.0.7

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

CISA 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.

Due date: 2025.06.09

1
Identify
Confirm that Synacor Zimbra Collaboration Suite (ZCS) and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CWE: CWE-79
KEV added: 2025.05.19
Ransomware use: 미확인