CVE-2025-66376

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

Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

CVSS 7.2 KEVNo patch available

This record: live connection— last retrieved: 7 November 2026 at 13:21.

Vendor

Synacor

Product

Zimbra Collaboration Suite (ZCS)

up to version cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*

Published

5 January 2026

Last modified

7 October 2026

Original source information

Taken directly from NVD, CISA or the vendor — sometimes in English, unchanged from the source.

Technical description

Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.

CVSS 3.1 — vector details

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Attack vector

NETWORK

Privileges required

NONE

User interaction

NONE

Confidentiality

Limited

Integrity

Limited

Availability

None

EPSS — Exploit Prediction Scoring System

Probability of exploitation within 30 days

20.2%

Percentile

97e

Source: FIRST.org, updated on 6 November 2026.

Patch information

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

IACS Radar assessment

Our own interpretation and context for the source data above.

IACS Radar assessment

Our own interpretation and context for this vulnerability — not an official source.

IACS Radar priority score

58/ 100

Based on CVSS 7.2, EPSS 20.2%, industrial relevance 30/100; raised due to confirmed active exploitation (KEV).

Combines CVSS, EPSS, KEV status, industrial relevance and exposure relevance — a complement to, not a replacement for, the individual scores below and above.

Conditions for exploitation

•Network access to the affected device or segment is required.
•No valid credentials are needed.
•No user interaction required.

Operational impact & energy relevance

Limited impact on availability; the risk lies mainly with confidentiality or integrity of process data.

No strong energy-sector-specific signals recognised; general OT/ICS relevance.

Recommended defensive measures

•Apply the latest firmware or software update and validate its integrity.
•Restrict network access to the affected device to a dedicated OT management segment.
•Implement network segmentation in line with zones and conduits (IEC 62443-3-2).
•Monitor for abnormal protocol traffic using an OT-aware detection system.

Industrial relevance score

30/ 100

• Included in the CISA KEV catalogue: confirmed evidence of actual exploitation.

Classification is provisional; manual verification by an OT security analyst is recommended.

Classified by IACS Radar-analysepijplijn (geautomatiseerd) on 7 November 2026.

IEC 62443 mapping

IEC 62443-4-1FR3 · Systeemintegriteit

Automatic IACS Radar assessment based on the reported CWE weakness classification; not an official certification statement.

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