{
    "dataType": "CVE_RECORD",
    "dataVersion": "5.2",
    "cveMetadata": {
        "cveId": "CVE-2026-107576",
        "assignerOrgId": "ceab7361-8a18-47b1-92ba-4d7d25f6715a",
        "state": "PUBLISHED",
        "assignerShortName": "GitLab",
        "dateReserved": "2026-10-08T10:51:45.640Z",
        "datePublished": "2026-10-08T11:46:56.083Z",
        "dateUpdated": "2026-10-08T11:46:56.083Z"
    },
    "containers": {
        "cna": {
            "title": "Inefficient Algorithmic Complexity in hMailServer",
            "descriptions": [
                {
                    "lang": "en",
                    "value": "Inefficient algorithmic complexity in the inbound DKIM and ARC signature verification of Progressive Robot hMailServer 6.0.0 through 6.3.5 allows a remote unauthenticated attacker to make the mail services unavailable by sending a message. Building the canonical header and choosing the header fields named in a signature's h= tag took time growing with the square of the message's header: the 'simple' canonicalisation prepended each continuation line of a folded field to the lines already gathered, and both canonicalisations searched the gathered fields from the bottom for each h= name and erased the match from the middle of the list. A message whose header holds very many fields, or a field folded over very many lines, with a DKIM-Signature the attacker signs for a domain they control, keeps a worker thread busy for tens of seconds per signature; up to ten signatures are evaluated per message by each of the DKIM and DMARC tests, on the threads that serve delivery and SMTP."
                }
            ],
            "affected": [
                {
                    "vendor": "Progressive Robot Ltd",
                    "product": "hMailServer",
                    "repo": "https://gitlab.com/hmailserver/hmailserver",
                    "versions": [
                        {
                            "version": "6.0.0",
                            "status": "affected",
                            "lessThan": "6.3.6",
                            "versionType": "semver"
                        }
                    ],
                    "defaultStatus": "unaffected"
                }
            ],
            "problemTypes": [
                {
                    "descriptions": [
                        {
                            "lang": "en",
                            "description": "CWE-407: Inefficient Algorithmic Complexity",
                            "cweId": "CWE-407",
                            "type": "CWE"
                        }
                    ]
                }
            ],
            "references": [
                {
                    "url": "https://gitlab.com/hmailserver/hmailserver/-/work_items/73"
                },
                {
                    "url": "https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6"
                }
            ],
            "metrics": [
                {
                    "format": "CVSS",
                    "scenarios": [
                        {
                            "lang": "en",
                            "value": "GENERAL"
                        }
                    ],
                    "cvssV3_1": {
                        "version": "3.1",
                        "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
                        "attackVector": "NETWORK",
                        "attackComplexity": "LOW",
                        "privilegesRequired": "NONE",
                        "userInteraction": "NONE",
                        "scope": "UNCHANGED",
                        "confidentialityImpact": "NONE",
                        "integrityImpact": "NONE",
                        "availabilityImpact": "HIGH",
                        "baseScore": 7.5,
                        "baseSeverity": "HIGH"
                    }
                }
            ],
            "solutions": [
                {
                    "lang": "en",
                    "value": "Upgrade to hMailServer 6.3.6, which builds the canonical header in one pass and chooses the h= fields from an index by name. Until then, lower the maximum message size, which bounds the cost."
                }
            ],
            "credits": [
                {
                    "lang": "en",
                    "value": "Found in the hMailServer project's own security review (Progressive Robot Ltd)",
                    "type": "finder"
                }
            ],
            "providerMetadata": {
                "orgId": "ceab7361-8a18-47b1-92ba-4d7d25f6715a",
                "shortName": "GitLab",
                "dateUpdated": "2026-10-08T11:46:56.083Z"
            }
        }
    }
}