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CVE-2026-33263

Status: DeferredMedium (4.3)—

When mail_max_userip_connections is set (default 10) and reached, submission-login can crash with epoll() panic caused by file descriptor handling issues. If running in high-security mode (default for community releases), only the new submission connection gets terminated. If running in high-performance mode (default for Pro releases), all connections handled by the submission-login process will be terminated. The crashes can cause failure for user to send a message, or it can cause duplicate messages to be sent.

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If TLS is not used (in the backend server processing the submission), duplicate deliveries cannot happen, because the crash can only happen at AUTH stage. Limit the number of connections handled by single submission-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Dovecot — DovecotAI

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2026-33263",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-33263",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-08-28T14:32:50.668040Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "security@open-xchange.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 4.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "LOW",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 2.8
      }
    ]
  },
  "affected": [
    {
      "source": "security@open-xchange.com",
      "affectedData": [
        {
          "vendor": "Open-Xchange GmbH",
          "modules": [
            "core"
          ],
          "product": "OX Dovecot Pro",
          "versions": [
            {
              "status": "affected",
              "version": "2.3.0",
              "lessThan": "2.3.22.2",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "3.0.0",
              "lessThan": "3.0.7",
              "versionType": "semver"
            },
            {
              "status": "affected",
              "version": "3.1.0",
              "lessThan": "3.1.6",
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        {
          "vendor": "Open-Xchange GmbH",
          "modules": [
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          "versions": [
            {
              "status": "affected",
              "version": "2.3.0",
              "lessThan": "2.4.5",
              "versionType": "semver"
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          "defaultStatus": "unaffected"
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  ],
  "published": "2026-08-28T12:16:27.483",
  "references": [
    {
      "url": "https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0003.json",
      "source": "security@open-xchange.com"
    }
  ],
  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "security@open-xchange.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-403"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "When mail_max_userip_connections is set (default 10) and reached, submission-login can crash with epoll() panic caused by file descriptor handling issues. If running in high-security mode (default for community releases), only the new submission connection gets terminated. If running in high-performance mode (default for Pro releases), all connections handled by the submission-login process will be terminated. The crashes can cause failure for user to send a message, or it can cause duplicate messages to be sent. If TLS is not used (in the backend server processing the submission), duplicate deliveries cannot happen, because the crash can only happen at AUTH stage. Limit the number of connections handled by single submission-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known."
    }
  ],
  "lastModified": "2026-09-03T18:13:44.643",
  "sourceIdentifier": "security@open-xchange.com"
}