CVE-2025-66376Zimbra 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.
Updated under an hour ago ()
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It affects Zimbra Collaboration and 1 other product. Add what you run to find out whether that includes you.
CISA lists it as known exploited since Mar 18, 2026; federal agencies had to remediate by Apr 1, 2026. Treat that date as your deadline.
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Free account, 1 product
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 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
- Weakness (CWE)
- CWE-79
- Known exploited
- Added to CISA KEV Mar 18, 2026; federal remediation due Apr 1, 2026Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- EPSS (exploitation in the next 30 days)
- 20.23% (percentile 97)
- Assigned by
- mitre
- NVD analysis
- Analyzed
- Record last updated
- Mar 19, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Zimbra Collaboration zimbra:collaboration (from the name) | from 10.0 before 10.0.18; from 10.1 before 10.1.13 | CNA record |
synacor zimbra_collaboration_suite synacor:zimbra_collaboration_suite | from 10.0.0 before 10.0.18; from 10.1.0 before 10.1.13 | NVD |
References
- https://wiki.zimbra.com/wiki/Zimbra_Security_Advisoriesvendor-advisory
- https://wiki.zimbra.com/wiki/Security_Centerrelease-notes, vendor-advisory
- https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policyproduct
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixesrelease-notes
- https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixesrelease-notes
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376us-government-resource
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.