Is It On KEV?

Synacor Zimbra Collaboration Suite (ZCS)

YES - ON THE CISA KEV LIST
CVE-2025-27915

Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability

CISA catalog due date2025-10-28
overdue since 2025-10-28
EPSS exploit probability (next 30 days)4.1% · 91percentile
From CVE publication to KEV listing209 days (2025-03-12 → 2025-10-07)
Remediation window (KEV listing to due date)21 days
Days on the KEV list400 days
Date added to KEV2025-10-07
Known ransomware campaign useUnknown
VendorSynacor
ProductZimbra Collaboration Suite (ZCS)
Weaknesses (CWE)CWE-79

Synacor: 19 entries (1.1% of all KEV entries are from this vendor); 5 added in 2026.

BOD 26-04 note: this is the date printed in the CISA catalog. A federal agency's actual deadline is set by its SSVC tier - Act (3 days), Attend (14 days), Track (60 days), or the next scheduled upgrade - counted from the KEV listing date or the date the vulnerability is identified in its environment, whichever comes first. Use the tier helper on each CVE page for your own window.

Your BOD 26-04 window (SSVC tier helper)

Your remediation window ends:

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.

Required action (CISA)

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Notes

https://wiki.zimbra.com/wiki/Security_Center ; https://nvd.nist.gov/vuln/detail/CVE-2025-27915

References

Other KEV entries for this vendor: Synacor

Synacor - Vendors with KEV entries

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