How severe is CVE-2024-27443?

CVE-2024-27443 has a CVSS score of 6.1/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2024-27443?

Affected package information for CVE-2024-27443 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2024-27443?

No fixed version has been published for CVE-2024-27443 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2024-27443 actively exploited in the wild?

No public exploit code has been indexed for CVE-2024-27443 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2024-27443?

CVE-2024-27443 has an EPSS (Exploit Prediction Scoring System) score of 32.9%, placing it in the 97th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score warrants monitoring and prompt remediation.

Is CVE-2024-27443 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2024-27443 (Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2025-05-19. CISA required all US federal civilian agencies to remediate this vulnerability by 2025-06-09. The required action was: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2024-27443?

CVE-2024-27443 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2024-27443?

A Nuclei detection template exists for CVE-2024-27443, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2024-27443 published, and has it been updated?

CVE-2024-27443 was published on August 12, 2024 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2024-27443: Cross-Site Scripting (Medium 6.1)

EPSS Exploitation Probability

via FIRST.org ↗

32.9%probability of exploitation in next 30 days

Moderate Risk97th percentile+0.45%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

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.

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2024-27443 in your stack?

O3 detects CVE-2024-27443 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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