Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
n/a — n/a
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.
5.4
3.9%
Vector breakdown
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
- Published
- Mar 12, 2025
- Modified
- Feb 26, 2026
- Added to KEV
- Oct 7, 2025
- Federal patch due
- Oct 28, 2025
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.
Weakness classification
Proof-of-concept & exploitation references
Weaponization
Public repositories whose name or description references CVE-2025-27915, found via a live GitHub search at request time. These are community-sourced signals, not a verified working exploit — cross-check each one before relying on it, and treat higher star counts and recent activity as (weak) corroboration, not proof.
No public GitHub repositories referencing CVE-2025-27915 were found at last check. Absence here is not proof no exploit exists — see the references below for vendor advisories and write-ups.
References
How this class of flaw gets exploited
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 base score of 5.4 out of 10 (CVSS 3.1).
Is CVE-2025-27915 actively exploited in the wild?
Yes. CVE-2025-27915 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added Oct 7, 2025, meaning CISA has confirmed evidence of active exploitation.
What is the EPSS score for CVE-2025-27915?
3.9% - meaning FIRST.org's EPSS model estimates a 3.9% probability this vulnerability will be exploited in the wild within 30 days (90% percentile among all scored CVEs).
Is there exploit tooling available for CVE-2025-27915?
Yes - a public Nuclei template referencing CVE-2025-27915 exist in public repositories we checked.
What type of vulnerability is CVE-2025-27915?
CVE-2025-27915 is classified under CWE-79 (CWE-79 Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')).
Cross-checked against
Impactr finds and proves whether CVE-2025-27915 — or flaws like it — are actually reachable in your own web apps and APIs, with a reproducible exploit as evidence.