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CVE-2025-66376: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
Synacor Zimbra Collaboration Suite (ZCS) · in CISA KEV since 2026-03-18
2026-03-18added to KEV
2026-04-01federal remediation due date
19.56%EPSS exploit probability (30 days) 97.3th percentile
6.1 MEDIUMCVSS 3.1
Unknownknown ransomware use
72days from NVD publication to KEV
What it is
Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML.
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.
| CWE | CWE-79 |
|---|---|
| CVSS vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |
| NVD published | 2026-01-05 (Analyzed) |
Original records: NVD · CISA KEV · JSON: /api/cve/CVE-2025-66376.json · all KEV CVEs
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Get the full file: Exploited Vulnerabilities Brief – September 2026 ($29): this month's KEV additions ranked by EPSS, ransomware use and due date, ready to hand to a patch team. Checkout by Polar.
Get the full file: Exploited Vulnerabilities Brief – September 2026 ($29): this month's KEV additions ranked by EPSS, ransomware use and due date, ready to hand to a patch team. Checkout by Polar.