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Known exploited vulnerability

CVE-2025-66376

mediumCVSS 3.1 6.1In CISA KEVEPSS 20%Published · Zimbra

The short answer

CVE-2025-66376 affects Zimbra Collaboration and is rated medium (CVSS 6.1). CISA added it to the Known Exploited Vulnerabilities catalog on 2026-03-18: attackers are using it, so patch it first.

What it is

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.

Weakness: CWE-79.

Severity

6.1 medium

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

Exploited (CISA KEV)

Yes, since Mar 18, 2026

Federal due date Apr 1, 2026

EPSS, next 30 days

20%

Higher than 97% of scored CVEs

How it can be exploited

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality impact
Low
Integrity impact
Low
Availability impact
None

What CISA says to do

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

Affected products

Collaboration. NVD's record lists the exact affected versions.

References

Questions

Is CVE-2025-66376 being exploited?

Yes. CISA added CVE-2025-66376 to its Known Exploited Vulnerabilities catalog on 2026-03-18, with a federal remediation due date of 2026-04-01.

How do I fix CVE-2025-66376?

CISA's 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.

From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.

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