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CISA KEV · Known exploitedMedium

CVE-2025-66376

Synacor Zimbra Collaboration Suite (ZCS)

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
6.1
EPSS
22.0%
97.4% percentile
CISA KEV
Listed
Published
2026.01.06
PRIORITY ASSESSMENT

Immediate review

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog.

Known exploitationConfirmed by CISA KEV
Exploit probability22.0%
Technical severityCVSS 6.1

Vulnerability overview

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.

Affected product and versions

Product
Synacor Zimbra Collaboration Suite (ZCS)
Affected versions
10.0, 10.1, >= 10.0.0 < 10.0.18, >= 10.1.0 < 10.1.13
Fixed versions
10.0.18, 10.1.13

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
CISA required action

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

Due date: 2026.04.01
  1. 1
    Identify

    Confirm that Synacor Zimbra Collaboration Suite (ZCS) and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CWE
CWE-79
KEV added
2026.03.18
Ransomware use
미확인
CVE-2025-66376 — Synacor Zimbra Collaboration Suite (ZCS) | SECUFOCUS NOW