CVE-2025-66376 (GCVE-0-2025-66376)
Vulnerability from cvelistv5 – Published: 2026-01-05 00:00 – Updated: 2026-03-19 03:55Summary
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.
Severity
7.2 (High)
SSVC
Exploitation: active
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-03-17 00:00 UTC
CWE
- CWE-79 - Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting')
Assigner
References
6 references
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Zimbra | Collaboration |
Affected:
10.0 , < 10.0.18
(custom)
Affected: 10.1 , < 10.1.13 (custom) cpe:2.3:a:zimbra:collaboration:*:*:*:*:*:*:*:* cpe:2.3:a:zimbra:collaboration:*:*:*:*:*:*:*:* |
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: d3a3c78e-2bfc-400c-9c61-58f999e9b108
Exploited: Yes
Timestamps
First Seen: 2026-03-18
Asserted: 2026-03-18
Scope
Notes: KEV entry: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability | Affected: Synacor / Zimbra Collaboration Suite (ZCS) | Description: Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML. | 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 | Known ransomware campaign use (KEV): Unknown | Notes (KEV): https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376
Evidence
Type: Vendor Report
Signal: Successful Exploitation
Confidence: 80%
Source: cisa-kev
Details
| Cwes | CWE-79 |
|---|---|
| Feed | CISA Known Exploited Vulnerabilities Catalog |
| Product | Zimbra Collaboration Suite (ZCS) |
| Due Date | 2026-04-01 |
| Date Added | 2026-03-18 |
| Vendorproject | Synacor |
| Vulnerabilityname | Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability |
| Knownransomwarecampaignuse | Unknown |
References
Created: 2026-03-18 18:00 UTC
| Updated: 2026-03-18 18:00 UTC
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 6dbfa806-400b-4204-83e4-3b4efbb6a0b5
Exploited: Yes
Timestamps
First Seen: 2026-06-01
Asserted: 2026-06-01
Scope
Notes: KEVIntel entry: 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... | Affected: Zimbra / Collaboration | CVSS: 7.2 (HIGH) | EPSS: 0.12009 | Used in malware: unknown | Not yet in CISA KEV: False
Evidence
Type: Public Report
Signal: Successful Exploitation
Confidence: 70%
Source: kevintel
Details
| Feed | KEVIntel (kevintel.com) |
|---|---|
| Title | 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... |
| Vendor | Zimbra |
| Product | Collaboration |
| Added Date | 2026-06-01T12:10:26.616Z |
| Cvss Score | 7.2 |
| Epss Score | 0.12009 |
| Cvss Severity | HIGH |
| Epss Percentile | 0.95594 |
| Used In Malware | unknown |
| Ahead Of Cisa Kev |
|
| Not Yet In Cisa Kev | False |
References
Created: 2026-06-23 14:03 UTC
| Updated: 2026-07-10 06:14 UTC
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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