# Synacor Zimbra Collaboration Suite (ZCS): Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability · pwn.watch

> Zimbra Collaboration contains a cross-site scripting (XSS) vulnerability in the CalendarInvite feature of the Zimbra webmail classic user interface. An attacker can exploit this vulnerability via an email message containing a crafted calendar header, leading to the execution of arbitrary JavaScript code. Added to CISA KEV on 2025-05-19.

Page: https://pwn.watch/i/synacor-zimbra-collaboration-suite-zcs-cve-2024-27443 · generated 2026-10-22T21:08:49.695Z

## Status
- Severity: medium · status: closed · patch: patched
- Product: Synacor Zimbra Collaboration Suite (ZCS)
- Started: 2025-05-19 · closed: 2025-05-19
- CVEs: CVE-2024-27443
- Affected: See vendor advisory / CISA notes (versions not always listed in KEV feed)
- Fixed in: See vendor advisory linked in sources

## Follow this incident
- RSS (one item per update): https://pwn.watch/i/synacor-zimbra-collaboration-suite-zcs-cve-2024-27443/feed.xml
- JSON Feed: https://pwn.watch/i/synacor-zimbra-collaboration-suite-zcs-cve-2024-27443/feed.json
- Full data (timeline, sources, posts, agentBrief): https://pwn.watch/i/synacor-zimbra-collaboration-suite-zcs-cve-2024-27443.json
- This file: https://pwn.watch/i/synacor-zimbra-collaboration-suite-zcs-cve-2024-27443/llms.txt

## Updates (newest first)
- 2025-05-19: CISA added CVE-2024-27443 to the KEV catalog (due 2025-06-09).

## Fix brief
# Security brief: Synacor Zimbra Collaboration Suite (ZCS): Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability

Source: https://pwn.watch/i/synacor-zimbra-collaboration-suite-zcs-cve-2024-27443 · status: closed (closed May 19, 2025) · severity: medium · updated May 19, 2025

## Patch status
**PATCHED: fixed releases exist. Upgrade to a fixed version.**

## What it is
Zimbra Collaboration contains a cross-site scripting (XSS) vulnerability in the CalendarInvite feature of the Zimbra webmail classic user interface. An attacker can exploit this vulnerability via an email message containing a crafted calendar header, leading to the execution of arbitrary JavaScript code. Added to CISA KEV on 2025-05-19.

Severity detail: CVSS 6.1 (CISA ADP, v3.1); actively exploited (CISA KEV)

- Product: Synacor Zimbra Collaboration Suite (ZCS)
- CVE / advisory ids: CVE-2024-27443

## Affected versions
- See vendor advisory / CISA notes (versions not always listed in KEV feed)

## Check whether you're affected
No generic command applies (the product is a hosted service, appliance or desktop app). Check the installed version in its admin UI / About screen and compare with the versions above.

## Fix
Upgrade to one of these fixed versions (or later on the same branch):
- See vendor advisory linked in sources

After upgrading, re-run the checks above and redeploy/restart the affected services.

## Latest updates
- May 19, 2025: CISA added CVE-2024-27443 to the KEV catalog (due 2025-06-09).

## Advisories
- [Synacor advisory: Synacor Zimbra Collaboration Suite (ZCS)](https://wiki.zimbra.com/wiki/Zimbra_Releases/8.8.15/P46#Security_Fixes) (Synacor)
- [Synacor advisory: Synacor Zimbra Collaboration Suite (ZCS)](https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P39#Security_Fixes) (Synacor)
- [Synacor advisory: Synacor Zimbra Collaboration Suite (ZCS)](https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.7#Security_Fixes) (Synacor)
- [NVD: CVE-2024-27443](https://nvd.nist.gov/vuln/detail/CVE-2024-27443) (NVD)
- [CISA Known Exploited Vulnerabilities Catalog](https://www.cisa.gov/known-exploited-vulnerabilities-catalog) (CISA)

## Caveats
Derived from CISA KEV JSON feed catalogVersion 2026.10.21. CVSS from the CVE record (cvelistV5). Exact affected/fixed version strings are not always in the KEV record; verify against the vendor advisory URL. startedAt uses dateAdded (exploitation may have begun earlier; many entries are older CVEs newly confirmed as exploited in 2025).

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Machine-readable: https://pwn.watch/i/synacor-zimbra-collaboration-suite-zcs-cve-2024-27443.json · all incidents: https://pwn.watch/incidents.json. Verify against the vendor advisory before changing production systems.