What is CVE-2025-27915?

CVE-2025-27915 is a medium-severity vulnerability in Synacor Zimbra Collaboration Suite, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2025-03-12.

How severe is CVE-2025-27915?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Is CVE-2025-27915 known to be exploited?

Yes. CVE-2025-27915 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-10-07), indicating it is being actively exploited. 5 public proof-of-concept repositories are indexed.

XSS in Synacor Zimbra Collaboration Suite

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.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2025-03-12 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.041 (90.5th percentile), scored 2026-10-19.

Low probability of exploitation in the next 30 days, but still tracked. 91st percentile — 90.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.040 · newest: 0.041 · change: +0.001

Affected products

Synacor Zimbra Collaboration Suite — versions 9.0.0

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2025-10-07. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2025-10-28.

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.

Public proof-of-concept exploits

References

wiki.zimbra.com/wiki/Security_Center (Release Notes)
wiki.zimbra.com/wiki/Zimbra_Releases/10.1.5 (Release Notes)
wiki.zimbra.com/wiki/Zimbra_Releases/10.0.13 (Release Notes)
wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P44 (Release Notes)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (Exploit, Third Party Advisory)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2025-27915?: CVE-2025-27915 is a medium-severity vulnerability in Synacor Zimbra Collaboration Suite, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2025-03-12.
How severe is CVE-2025-27915?: Medium severity. CVSS v3 base score is 5.4 out of 10.
Is CVE-2025-27915 known to be exploited?: Yes. CVE-2025-27915 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-10-07), indicating it is being actively exploited. 5 public proof-of-concept repositories are indexed.