Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2024-27443

Zimbra Collaboration (ZCS) Cross-Site Scripting

Zimbra Collaboration (ZCS)

Watch CVE-2024-27443 Browse KEV feed
Severity
CVSS 6.1 · Medium
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
23.6%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2024-27443 is an unauthenticated vulnerability affecting Zimbra Collaboration (ZCS). An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0. A Cross-Site Scripting (XSS) vulnerability exists in the...

Is it exploited?

Yes. Previdian tracks this CVE as a known exploited vulnerability. Confidence is confirmed. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

Zimbra Collaboration (ZCS).

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0

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.

Published
12 Aug 2024
Exploitation Reported
21 May 2025
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
Required

Tags

cisa nuclei_scanner

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CVE

Recorded 21 May 2025

A trusted third party reported exploitation.

Proof of concept available

Nuclei Templates

Recorded 12 Jun 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

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Source Added
CVE First 2025-05-21 13:10 UTC
CISA 2026-06-02 14:07 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2024/CVE-2024-27443.yaml 01 Jun 2026

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

6.1 Medium

Potential damage if exploited. Separate from whether attackers are using it.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

23.6%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') CWE-79

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

Zimbra Collaboration - Cross-Site Scripting (XSS)

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 14:21 UTC

    Public PoC available

    Public proof-of-concept code published

  2. 14:07 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  3. 15:34 UTC

    Nuclei template available

    Scanner coverage available

  4. 13:10 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  5. 00:00 UTC

    CVE published

    Vulnerability disclosed publicly

  6. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2024-27443

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2024-27443",
  "confidence": "Confirmed",
  "cvss_score": 6.1,
  "cvss_estimated": false,
  "epss_score": 0.23632,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}