CVE-2026-107569

{
  "id": "CVE-2026-107569",
  "sourceIdentifier": "[email protected]",
  "published": "2026-10-19T16:17:01.830",
  "lastModified": "2026-10-20T20:17:13.973",
  "vulnStatus": "Deferred",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Unchecked input for a loop condition in Progressive Robot hMailServer 6.0.0 through 6.3.6 allows a remote unauthenticated attacker to stop the server carrying mail. The server bounds the mail it generates in response to a message - a rule forward, reply or copy, an account forward, a Sieve redirect, vacation or notify, a bounce, an out-of-office reply - by a counter it carries in the message's X-hMailServer-LoopCount header, and makes no more once the counter reaches the configured rule loop limit (5 by default); that is what ends a forwarding or auto-reply cycle in a bounded number of hops. X-hMailServer-LoopCount is an ordinary header that is not stripped from mail arriving from outside, and the server read it with a signed conversion and no validation, so a count below zero passed every test against the limit: a sender who sets X-hMailServer-LoopCount to a negative value, or on the Linux builds to a value above the 32-bit signed range that the conversion wraps to a negative one, lifts the bound, and a message that enters a generated-mail cycle then loops up to about two thousand million times, each hop a queued message and a delivery, filling the queue and disk and stopping mail service. The Sieve notify action (from 6.2.22) consulted no limit at all, and its increment of the count could overflow a signed integer; and an account could reset the counter on its own mail through a Sieve editheader of the header (from 6.2.22) or a rule Set header value action (all versions) ahead of a forward or redirect."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "Progressive Robot Ltd",
          "product": "hMailServer",
          "defaultStatus": "unaffected",
          "repo": "https://gitlab.com/hmailserver/hmailserver",
          "versions": [
            {
              "version": "6.0.0",
              "lessThanOrEqual": "6.3.6",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-10-20T19:27:14.386515Z",
          "id": "CVE-2026-107569",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-606"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7",
      "source": "[email protected]"
    },
    {
      "url": "https://gitlab.com/hmailserver/hmailserver/-/work_items/81",
      "source": "[email protected]"
    }
  ]
}