No. CVE-2025-27915
A Synacor Zimbra Collaboration Suite (ZCS) bug is being used in attacks
Yes. Attackers are using this right now.
What to do
Apply the vendor's update. If there is none, stop using it or cut it off from the internet.
- Confirmed in attacks
- Oct 7, 2025
- Product
- Synacor Zimbra Collaboration Suite (ZCS)
- Attack likelihood, next 30 days
- 4.1%
Attack likelihood is EPSS, a daily estimate from FIRST.org of how likely this bug is to be used in attacks in the next 30 days.
The official description
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.
For your tech helper
A read-only checklist for whoever helps you with your computer, or an AI assistant. Paste it into Claude, ChatGPT or a coding agent; it only looks and changes nothing.
Read-only check, change nothing, send nothing anywhere.
Is Synacor Zimbra Collaboration Suite (ZCS) (CVE-2025-27915) installed or running on this machine or in this project?
1. Find every copy and its version (apps, packages, containers, lockfiles).
2. Compare each version against the vendor's fixed version for CVE-2025-27915. Quote the vendor page you used.
3. Report a table: where, version, fixed version, status (exposed / fixed / not installed / unsure).
4. List the exact update steps, but do not run them.