CVE-2025-27915

CVE-2025-27915 is a medium-severity vulnerability in Synacor Zimbra Collaboration Suite with a CVSS 3.x base score of 5.4. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2025-10-07). The underlying weakness is classified as CWE-79.

Key facts

Description

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 <details> 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.

Frequently asked questions

What is CVE-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 malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a <details> 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.
How severe is CVE-2025-27915?
CVE-2025-27915 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2025-27915 being actively exploited?
Yes. CVE-2025-27915 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2025-10-07, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2025-27915?
CVE-2025-27915 primarily affects Synacor Zimbra Collaboration Suite. In total, 46 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2025-27915?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2025-27915 have an EU (EUVD) identifier?
Yes. CVE-2025-27915 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-7823. It is also flagged as exploited in the EUVD (since 2025-10-07).
When was CVE-2025-27915 published?
CVE-2025-27915 was published on 2025-03-12 and last updated on 2026-06-17.

References

Affected products (46)

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