Unchecked Input for Loop Condition in hMailServer

{
  "id": "767e35bf1d551d4640c405c7220ac9ea39f4668f62b40c67f98a6dca2fffec9a",
  "url": "https://osv.dev/vulnerability/CVE-2026-107569",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Unchecked Input for Loop Condition in hMailServer",
    "summary": "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) ah",
    "evidence": "osv:CVE-2026-107569",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-107569",
      "aliases": [
        "CVE-2026-107569"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://gitlab.com/hmailserver/hmailserver",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e4b7163189ac6ce365bb954cf3e264e2e3105a18"
                },
                {
                  "last_affected": "e3c448aa66fc310b74d076884d54fae951296915"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "6.0.0"
                      },
                      {
                        "last_affected": "6.3.6"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "6.0.0"
                      },
                      {
                        "last_affected": "6.3.6"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v6.3.6",
            "v6.3.5",
            "v6.3.4",
            "v6.3.3",
            "v6.3.2",
            "build-inputs-1",
            "v6.3.1",
            "v6.3.0",
            "v6.2.28",
            "v6.2.27",
            "v6.2.26",
            "v6.2.25",
            "v6.2.24",
            "v6.2.23-alpha2",
            "v6.2.23-alpha1",
            "v6.2.22-pre6",
            "v6.2.22-pre5",
            "v6.2.22-pre4",
            "v6.2.22-pre3",
            "v6.2.22-pre2",
            "v6.2.22-pre1",
            "v6.2.21",
            "v6.2.20",
            "v6.2.19",
            "v6.2.18",
            "v6.2.17",
            "v6.2.16",
            "v6.2.15",
            "v6.2.14",
            "v6.2.13",
            "v6.2.12",
            "v6.2.11",
            "v6.2.10",
            "v6.2.9",
            "v6.2.8",
            "v6.2.7",
            "v6.2.6",
            "v6.2.5",
            "v6.2.4",
            "v6.2.3",
            "v6.2.2",
            "v6.2.1",
            "v6.2.0",
            "v6.1.0",
            "v6.0.0-B4",
            "v6.0.0-B3",
            "v6.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-107569.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:52.329982110Z",
      "provider": "osv",
      "references": [
        "https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7",
        "https://gitlab.com/hmailserver/hmailserver/-/work_items/81",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107569.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-107569",
        "https://gitlab.com/hmailserver/hmailserver"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-606"
        ],
        "cna_assigner": "GitLab",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107569.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-107569",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 521325,
  "published_at": "2026-10-19T15:34:37.492+00:00"
}