Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar REPLY Attendee Response

{
  "id": "747f43757a93faa1114a3f0c6aafdb8dbafa5f43f2ef29e7b0b8e995b677d7d7",
  "url": "https://www.cve.org/CVERecord?id=CVE-2026-93628",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar REPLY Attendee Response",
    "summary": "An attendee authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to forge another attendee's response to an existing meeting. Zimbra passes a null sender identity when processing iCalendar REPLY components, causing the attendee authorization filter to be skipped. An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar. The change occurs automatically during delivery without organizer or attendee interaction. ZCS 10.1.16 and 10.1.21 are affected.",
    "evidence": "cve:CVE-2026-93628",
    "products": [
      {
        "name": {
          "value": "Zimbra Collaboration Suite",
          "evidence": "/containers/cna/affected/0/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-93628",
      "aliases": [
        "CVE-2026-93628"
      ],
      "metrics": [
        {
          "format": "CVSS",
          "cvssV3_1": {
            "scope": "UNCHANGED",
            "version": "3.1",
            "baseScore": 5.3,
            "attackVector": "NETWORK",
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N",
            "integrityImpact": "LOW",
            "userInteraction": "NONE",
            "attackComplexity": "LOW",
            "availabilityImpact": "NONE",
            "privilegesRequired": "NONE",
            "confidentialityImpact": "NONE"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "affected": [
        {
          "vendor": "Zimbra",
          "product": "Zimbra Collaboration Suite",
          "versions": [
            {
              "status": "affected",
              "version": "0",
              "versionType": "semver",
              "lessThanOrEqual": "10.1.21"
            }
          ],
          "defaultStatus": "unaffected"
        }
      ],
      "modified": "2026-10-28T20:02:01.885Z",
      "provider": "cve",
      "references": [
        "https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories",
        "https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/"
      ],
      "provider_metadata": {
        "adp": [
          {
            "title": "CISA ADP Vulnrichment",
            "metrics": [
              {
                "other": {
                  "type": "ssvc",
                  "content": {
                    "id": "CVE-2026-93628",
                    "role": "CISA Coordinator",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "yes"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "version": "2.0.3",
                    "timestamp": "2026-10-28T18:23:55.530504Z"
                  }
                }
              }
            ],
            "providerMetadata": {
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP",
              "dateUpdated": "2026-10-28T20:02:01.885Z"
            }
          }
        ],
        "cna": {
          "orgId": "9974b330-7714-4307-a722-5648477acda7",
          "shortName": "rapid7",
          "dateUpdated": "2026-10-23T13:18:16.368Z"
        }
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-93628",
        "evidence": "/cveMetadata/cveId"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/containers/cna/metrics"
  },
  "source_id": "core-cve",
  "document_id": 484712,
  "published_at": "2026-10-23T13:18:16.368+00:00"
}