CVE-2024-27443: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
Affects Synacor Zimbra Collaboration Suite (ZCS)Source CISA KEV
Exploited in the wild · KEV due 9 Jun 2025 · public detection template (Nuclei) · 24% EPSS : apply the vendor's fix or mitigations to Synacor Zimbra Collaboration Suite (ZCS) now.
Data as of 10/24/2026, 22:15:59 UTC
- Exploitation
Actively exploited – in CISA KEV since 05/19/2025
- KEV deadline
- 06/09/2025 US federal agencies must patch by this date; a sensible deadline for everyone else.
- EPSS
- 24.6% chance of exploitation in 30 days – higher than 97% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Public exploits
- a Nuclei detection templatePublic attack or detection tooling exists; see Public exploits below.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:NWhat to do
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.
Public exploits and detection
Nuclei detection templates
Public tooling indexed from Metasploit Framework, Exploit-DB and ProjectDiscovery nuclei-templates. Its existence raises the odds of exploitation; it does not confirm attacks.
Description
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.
Weaknesses
- CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #1OWASP Top 10 A05:2025: Injection (opens in a new tab)
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
References
- wiki.zimbra.com/wiki/Zimbra_Releases/8.8.15/P46 (opens in a new tab)
- wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P39 (opens in a new tab)
- wiki.zimbra.com/wiki/Zimbra_Releases/10.0.7 (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2024-27443 (opens in a new tab)
- cisa.gov/known-exploited-vulnerabilities-catalog?search=CVE-2024-27443 (opens in a new tab)