CVE-2025-27915
Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 28 October 2025). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
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.
- CVSS 3.1
- 5.4 MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
- EPSS
- 3.99% probability · 90th percentile
- CISA KEV
- Listed 7 October 2025 · due 28 October 2025
- Weakness
- CWE-79
- Affected
- synacor/zimbra collaboration suite
- Source
- cve@mitre.org
CISA notes
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. https://wiki.zimbra.com/wiki/Security_Center ; https://nvd.nist.gov/vuln/detail/CVE-2025-27915
References
- https://wiki.zimbra.com/wiki/Security_CenterRelease Notes
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.13#Security_FixesRelease Notes
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.5#Security_FixesRelease Notes
- https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P44#Security_FixesRelease 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-2025-27915US Government Resource
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.