CVEs / CVE-2025-27915
CVE-2025-27915: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
- Known exploited in the CISA KEV catalog since 7 Oct 2025
- medium 5.4 CVSS 3.1 (from the CNA)
- EPSS 4.06% chance of exploitation in the next 30 days, higher than 90% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
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 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.
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.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| n/a n/a | n/a | — |
Exploitation
| In CISA KEV since | 7 Oct 2025 |
|---|---|
| Due date for US federal agencies | 28 Oct 2025 |
| Used in ransomware campaigns | Unknown |
| 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. |
Severity
| CVSS 3.1 | 5.4 mediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:NScored by the CNA (134c704f-9b21-4f2e-91b3-4a467353bcc0) |
|---|---|
| Weakness | CWE-79 |
References
- CVE-2025-27915 on NVD
- CVE-2025-27915 in the CISA KEV catalog
- https://wiki.zimbra.com/wiki/Security_Center (cited by CISA)
- CVE-2025-27915 on OSV
- https://wiki.zimbra.com/wiki/Security_Center Release Notes
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.13#Security_Fixes Release Notes
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.5#Security_Fixes Release Notes
- https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P44#Security_Fixes Release Notes
- https://strikeready.com/blog/0day-ics-attack-in-the-wild/ Exploit, Third Party Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-27915 US Government Resource
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.