ZDF
Sign inSign up

Vulnerabilities

Vulnerability · CVE-2025-27915

Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability

Published Mar 12, 2025 · catalog updated Jun 17, 2026 · Synacor Zimbra Collaboration Suite (ZCS)

Patch now

CVE-2025-27915 is in the CISA known-exploited catalog, due Oct 28, 2025. Confirm Synacor Zimbra Collaboration Suite (ZCS) against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Severity
Medium5.4
Known exploitation
CISA KEV and VulnCheck KEV
EPSS
4.06%
Remediation
Remediation guidance
Affected products
cpe synacor/zimbra collaboration suite · vendor Synacor Zimbra Collaboration Suite (ZCS)

An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a tag. This allows an attacker to run arbitrary JavaScript within the victim's session, potentially leading to unauthorized actions such as setting e-mail filters to redirect messages to an attacker-controlled address. As a result, an attacker can perform unauthorized actions on the victim's account, including e-mail redirection and data exfiltration.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe synacor/zimbra collaboration suite9.0.0
  • vendor Synacor Zimbra Collaboration Suite (ZCS)version unspecified

How to fix CVE-2025-27915

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2025-27915 is in the CISA known-exploited catalog, due Oct 28, 2025. Confirm Synacor Zimbra Collaboration Suite (ZCS) against the vendor advisory and apply that fix. The CVSS score does not change the priority.

Which versions are affected?

Compare what you have installed with synacor/zimbra collaboration suite 9.0.0. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

What should an analyst verify?

CWE-79: Cross-site Scripting (XSS). EPSS 4.06%. The CISA KEV listing is the exploitation evidence. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 12, 2025 · Catalog

    Detected

    An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a tag. This allows an attacker to run arbitra

  2. Oct 7, 2025 · CISA KEV

    Known exploited

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

  3. Oct 28, 2025 · CISA KEV

    Remediation due

    Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

  4. Jun 17, 2026 · Catalog

    Updated

    An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a tag. This allows an attacker to run arbitra

Sources

  • CISA KEVConfirmed exploitationCVE-2025-27915

    Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a tag. This allows an attacker to run arbitrary JavaScript within the victim's s

    cisa.gov
  • CVE.orgVulnerability recordCVE-2025-27915

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-27915

    30-day exploitation probability 4.1%

    first.org
  • NIST NVDVulnerability recordCVE-2025-27915

    An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a maliciou

    nvd.nist.gov
  • VulnCheck KEVConfirmed exploitationCVE-2025-27915

    Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScrip

    vulncheck.com

References

Freshness

Last verified in this catalog Oct 17, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.