GCVE Workshop - 22 September 2026 (14:00-18:00), Luxembourg Before The Vulnopticon Conference - Registration

CVE-2025-66376 (GCVE-0-2025-66376)

Vulnerability from cvelistv5 – Published: 2026-01-05 00:00 – Updated: 2026-03-19 03:55
VLAI CISA Previdian
Summary
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)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
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
Impacted products
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:*:*:*:*:*:*:*:*
Create a notification for this product.
CISA
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: d3a3c78e-2bfc-400c-9c61-58f999e9b108

Vulnerability ID: CVE-2025-66376

Status: Confirmed

Status Updated: 2026-03-18 00:00 UTC

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

Vulnerability ID: CVE-2025-66376

Status: Confirmed

Status Updated: 2026-06-01 12:10 UTC

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 
{
  "count": 1,
  "unit": "day"
}
Not Yet In Cisa Kev False
References
Created: 2026-06-23 14:03 UTC | Updated: 2026-07-10 06:14 UTC
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2025-66376",
                "options": [
                  {
                    "Exploitation": "active"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-03-17T00:00:00+00:00",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          },
          {
            "other": {
              "content": {
                "dateAdded": "2026-03-18",
                "reference": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376"
              },
              "type": "kev"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-03-19T03:55:17.926Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "government-resource"
            ],
            "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376"
          }
        ],
        "timeline": [
          {
            "lang": "en",
            "time": "2026-03-18T00:00:00.000Z",
            "value": "CVE-2025-66376 added to CISA KEV"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Collaboration",
          "vendor": "Zimbra",
          "versions": [
            {
              "lessThan": "10.0.18",
              "status": "affected",
              "version": "10.0",
              "versionType": "custom"
            },
            {
              "lessThan": "10.1.13",
              "status": "affected",
              "version": "10.1",
              "versionType": "custom"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:a:zimbra:collaboration:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "10.0.18",
                  "versionStartIncluding": "10.0",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:a:zimbra:collaboration:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "10.1.13",
                  "versionStartIncluding": "10.1",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.2,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-79",
              "description": "CWE-79 Improper Neutralization of Input During Web Page Generation (XSS or \u0027Cross-site Scripting\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-01-05T14:49:53.107Z",
        "orgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca",
        "shortName": "mitre"
      },
      "references": [
        {
          "url": "https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories"
        },
        {
          "url": "https://wiki.zimbra.com/wiki/Security_Center"
        },
        {
          "url": "https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy"
        },
        {
          "url": "https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes"
        },
        {
          "url": "https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes"
        }
      ],
      "x_generator": {
        "engine": "enrichogram 0.0.1"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "8254265b-2729-46b6-b9e3-3dfca2d5bfca",
    "assignerShortName": "mitre",
    "cveId": "CVE-2025-66376",
    "datePublished": "2026-01-05T00:00:00.000Z",
    "dateReserved": "2025-11-28T00:00:00.000Z",
    "dateUpdated": "2026-03-19T03:55:17.926Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "cisa_known_exploited": {
      "cveID": "CVE-2025-66376",
      "cwes": "[\"CWE-79\"]",
      "dateAdded": "2026-03-18",
      "dueDate": "2026-04-01",
      "forensicTriage": "No",
      "knownRansomwareCampaignUse": "Unknown",
      "notes": "https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376",
      "product": "Zimbra Collaboration Suite (ZCS)",
      "requiredAction": "Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.",
      "shortDescription": "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.",
      "vendorProject": "Synacor",
      "vulnerabilityName": "Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability"
    },
    "epss": {
      "cve": "CVE-2025-66376",
      "date": "2026-09-16",
      "epss": "0.19559",
      "percentile": "0.97241"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-66376\",\"sourceIdentifier\":\"cve@mitre.org\",\"published\":\"2026-01-05T15:15:44.903\",\"lastModified\":\"2026-06-17T09:56:44.753\",\"vulnStatus\":\"Analyzed\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"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\":[{\"source\":\"cve@mitre.org\",\"affectedData\":[{\"vendor\":\"Zimbra\",\"product\":\"Collaboration\",\"defaultStatus\":\"unaffected\",\"versions\":[{\"version\":\"10.0\",\"lessThan\":\"10.0.18\",\"versionType\":\"custom\",\"status\":\"affected\"},{\"version\":\"10.1\",\"lessThan\":\"10.1.13\",\"versionType\":\"custom\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"cve@mitre.org\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N\",\"baseScore\":7.2,\"baseSeverity\":\"HIGH\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"CHANGED\",\"confidentialityImpact\":\"LOW\",\"integrityImpact\":\"LOW\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":3.9,\"impactScore\":2.7},{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N\",\"baseScore\":6.1,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"REQUIRED\",\"scope\":\"CHANGED\",\"confidentialityImpact\":\"LOW\",\"integrityImpact\":\"LOW\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":2.8,\"impactScore\":2.7}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-03-17T00:00:00+00:00\",\"id\":\"CVE-2025-66376\",\"options\":[{\"exploitation\":\"active\"},{\"automatable\":\"no\"},{\"technicalImpact\":\"partial\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"cisaExploitAdd\":\"2026-03-18\",\"cisaActionDue\":\"2026-04-01\",\"cisaRequiredAction\":\"Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.\",\"cisaVulnerabilityName\":\"Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability\",\"weaknesses\":[{\"source\":\"cve@mitre.org\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-79\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"10.0.0\",\"versionEndExcluding\":\"10.0.18\",\"matchCriteriaId\":\"7D423DB3-FCD4-445F-A778-BC5F83E01953\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"10.1.0\",\"versionEndExcluding\":\"10.1.13\",\"matchCriteriaId\":\"7C3F6B1E-1671-461B-A093-7B6854C227FE\"}]}]}],\"references\":[{\"url\":\"https://wiki.zimbra.com/wiki/Security_Center\",\"source\":\"cve@mitre.org\",\"tags\":[\"Release Notes\",\"Vendor Advisory\"]},{\"url\":\"https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes\",\"source\":\"cve@mitre.org\",\"tags\":[\"Release Notes\"]},{\"url\":\"https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes\",\"source\":\"cve@mitre.org\",\"tags\":[\"Release Notes\"]},{\"url\":\"https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy\",\"source\":\"cve@mitre.org\",\"tags\":[\"Product\"]},{\"url\":\"https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories\",\"source\":\"cve@mitre.org\",\"tags\":[\"Vendor Advisory\"]},{\"url\":\"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376\",\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"tags\":[\"US Government Resource\"]}]}}",
    "redhat_vex": {
      "current_release_date": "2026-03-27T08:24:08+00:00",
      "cve": "CVE-2025-66376",
      "id": "CVE-2025-66376",
      "initial_release_date": "2025-01-01T00:00:00+00:00",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "CVE-2025-66376",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-66376.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2025-66376\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"active\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-03-18T16:58:05.651376Z\"}}}, {\"other\": {\"type\": \"kev\", \"content\": {\"dateAdded\": \"2026-03-18\", \"reference\": \"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376\"}}}], \"references\": [{\"url\": \"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376\", \"tags\": [\"government-resource\"]}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-01-05T20:42:37.847Z\"}, \"timeline\": [{\"lang\": \"en\", \"time\": \"2026-03-18T00:00:00.000Z\", \"value\": \"CVE-2025-66376 added to CISA KEV\"}]}], \"cna\": {\"metrics\": [{\"cvssV3_1\": {\"version\": \"3.1\", \"baseScore\": 7.2, \"baseSeverity\": \"HIGH\", \"vectorString\": \"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N\"}}], \"affected\": [{\"vendor\": \"Zimbra\", \"product\": \"Collaboration\", \"versions\": [{\"status\": \"affected\", \"version\": \"10.0\", \"lessThan\": \"10.0.18\", \"versionType\": \"custom\"}, {\"status\": \"affected\", \"version\": \"10.1\", \"lessThan\": \"10.1.13\", \"versionType\": \"custom\"}], \"defaultStatus\": \"unaffected\"}], \"references\": [{\"url\": \"https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories\"}, {\"url\": \"https://wiki.zimbra.com/wiki/Security_Center\"}, {\"url\": \"https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy\"}, {\"url\": \"https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes\"}, {\"url\": \"https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes\"}], \"x_generator\": {\"engine\": \"enrichogram 0.0.1\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"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.\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-79\", \"description\": \"CWE-79 Improper Neutralization of Input During Web Page Generation (XSS or \u0027Cross-site Scripting\u0027)\"}]}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:a:zimbra:collaboration:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"10.0.18\", \"versionStartIncluding\": \"10.0\"}, {\"criteria\": \"cpe:2.3:a:zimbra:collaboration:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"10.1.13\", \"versionStartIncluding\": \"10.1\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"8254265b-2729-46b6-b9e3-3dfca2d5bfca\", \"shortName\": \"mitre\", \"dateUpdated\": \"2026-01-05T14:49:53.107Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2025-66376\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-03-19T03:55:17.926Z\", \"dateReserved\": \"2025-11-28T00:00:00.000Z\", \"assignerOrgId\": \"8254265b-2729-46b6-b9e3-3dfca2d5bfca\", \"datePublished\": \"2026-01-05T00:00:00.000Z\", \"assignerShortName\": \"mitre\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





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.


Detection rules are retrieved from Rulezet.


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.