What it is
CVE-2025-66376 is an unauthenticated vulnerability affecting Zimbra Collaboration. 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)...
Vulnerability report
Exploited in the wild
Confirmed confidence
In CISA KEV
CVE-2025-66376
Collaboration Cross-Site Scripting
Zimbra / Collaboration · affected before 10.0.18
- Severity
- CVSS 7.2 · High
- Confidence
- Confirmed
- Exploit status
- Exploited in the wild
- EPSS
- 22.0%
- First observed
- —
- Last observed
- —
Decision summary
What security teams need to know first
Direct answers before the deeper technical record.
Is it exploited?
Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.
Who is affected?
Zimbra / Collaboration affected before 10.0.18.
What should we do?
Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
Overview
Collaboration Cross-Site Scripting
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.
Vendor
Product
Affected
Status
Zimbra
Collaboration
Before 10.0.18
Affected
Zimbra
Collaboration
Before 10.1.13
Affected
- Published
- 05 Jan 2026
- Exploitation Reported
- 01 Jun 2026
- Attack vector
- Remote
- Complexity
- Low
- Privileges
- None
- User interaction
- None
Tags
cisa
CVE References
- CVE Record CVE.org · CVE Record https://www.cve.org/CVERecord?id=CVE-2025-66376
- wiki.zimbra.com/wiki/Zimbra_Security_Advisories wiki.zimbra.com · CVE Record https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
- wiki.zimbra.com/wiki/Security_Center wiki.zimbra.com · CVE Record https://wiki.zimbra.com/wiki/Security_Center
- wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy wiki.zimbra.com · CVE Record https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy
- wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13 wiki.zimbra.com · CVE Record https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes
- wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18 wiki.zimbra.com · CVE Record https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes
Exploitation evidence
Why KEV Intelligence marks this CVE as exploited
Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.
Exploited in the wild
CVE
Independent exploitation attestation added to the KEV Intelligence record.
Known exploited vulnerability sources
Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.
Learn about Pro API access| Source | Added |
|---|---|
| CVE First | 2026-06-01 12:10 UTC |
| CISA | 2026-06-02 14:02 UTC |
Detection
Operational artifacts and observed signals
Make the evidence actionable in scanner, SOC, and edge-control workflows.
Observed signals
- Request targets
- 0
- User-Agents
- 0
Raw values available in Pro and Enterprise.
Scanner coverage
No scanner integrations recorded yet.
Virtual patch status
No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.
Learn about virtual patches →No detection artifacts or sensor request patterns are available for this CVE yet.
Check back as sensor telemetry and scanner integrations are updated.
Risk and context
Severity, weaknesses, and research context
CVSS v3.1
7.2
High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
EPSS
22.0%
Timeline
From disclosure to observed exploitation
-
Added to CISA KEV
Listed in the CISA Known Exploited Vulnerabilities catalog
-
Added to KEV Intelligence KEV Feed
High-confidence, third-party attested exploitation
-
CVE published
Vulnerability disclosed publicly
-
CVE ID reserved
Identifier reserved by the CNA
Pro API
Automate this intelligence
Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.
- Evidence confidence and provenance
- First-party sensor telemetry
- PoC and scanner references
- Affected versions and enrichment
- Automation-ready JSON delivery
GET /api/v2/pro/kevs/CVE-2025-66376
Free JSON includes basic KEV fields{
"cve_id": "CVE-2025-66376",
"confidence": "Confirmed",
"cvss_score": 7.2,
"cvss_estimated": false,
"epss_score": 0.21973,
"exploit_status": {
"exploited_in_the_wild": true,
"active_exploitation_observed": false
},
"sensor_telemetry": { "attempts": 0, "sensors": 0 }
}Early warning alerts
Get alerts on high-impact exploitation
Receive curator-selected alerts when exploitation activity warrants attention. Each alert includes the evidence and context needed to decide what requires attention now.