Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
n/a — n/a
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.
6.1
20.8%
Vector breakdown
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- Published
- Aug 12, 2024
- Modified
- Oct 21, 2025
- Added to KEV
- May 19, 2025
- Federal patch due
- Jun 9, 2025
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.
Weakness classification
Proof-of-concept & exploitation references
Weaponization
Public repositories whose name or description references CVE-2024-27443, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit - cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
No public GitHub repositories referencing CVE-2024-27443 were found at last check. Absence here is not proof no exploit exists - see the references below for vendor advisories and write-ups.
References
Frequently asked questions
What is CVE-2024-27443?
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.
How severe is CVE-2024-27443?
CVE-2024-27443 has a CVSS base score of 6.1 out of 10 (CVSS 3.1).
Is CVE-2024-27443 actively exploited in the wild?
Yes. CVE-2024-27443 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added May 19, 2025, meaning CISA has confirmed evidence of active exploitation.
What is the EPSS score for CVE-2024-27443?
20.8% - meaning FIRST.org's EPSS model estimates a 20.8% probability this vulnerability will be exploited in the wild within 30 days (97% percentile among all scored CVEs).
Is there exploit tooling available for CVE-2024-27443?
Yes - a public Nuclei template referencing CVE-2024-27443 exist in public repositories we checked.
What type of vulnerability is CVE-2024-27443?
CVE-2024-27443 is classified under CWE-79 (CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')).
Cross-checked against
Impactr finds and proves whether CVE-2024-27443 - or flaws like it - are actually reachable in your own web apps and APIs, with a reproducible exploit as evidence.
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