{"api_version":"1","generated_at":"2026-10-08T14:57:33+00:00","cve":"CVE-2026-107576","urls":{"html":"https://cve.report/CVE-2026-107576","api":"https://cve.report/api/cve/CVE-2026-107576.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-107576","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-107576"},"summary":{"title":"Inefficient Algorithmic Complexity in hMailServer","description":"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.","state":"PUBLISHED","assigner":"GitLab","published_at":"2026-10-08 12:17:15","updated_at":"2026-10-08 12:17:15"},"problem_types":["CWE-407","CWE-407 CWE-407: Inefficient Algorithmic Complexity"],"metrics":[{"version":"3.1","source":"cve@gitlab.com","type":"Secondary","score":"7.5","severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","data":{"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"}},{"version":"3.1","source":"CNA","type":"CVSS","score":"7.5","severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","data":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":7.5,"baseSeverity":"HIGH","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"}}],"references":[{"url":"https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6","name":"https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6","refsource":"cve@gitlab.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://gitlab.com/hmailserver/hmailserver/-/work_items/73","name":"https://gitlab.com/hmailserver/hmailserver/-/work_items/73","refsource":"cve@gitlab.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-107576","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107576","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Progressive Robot Ltd","product":"hMailServer","version":"affected 6.0.0 6.3.6 semver","platforms":[]}],"timeline":[],"solutions":[{"source":"CNA","title":"","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.","time":"","lang":"en"}],"workarounds":[],"exploits":[],"credits":[{"source":"CNA","value":"Found in the hMailServer project's own security review (Progressive Robot Ltd)","lang":"en"}],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"hMailServer","repo":"https://gitlab.com/hmailserver/hmailserver","vendor":"Progressive Robot Ltd","versions":[{"lessThan":"6.3.6","status":"affected","version":"6.0.0","versionType":"semver"}]}],"credits":[{"lang":"en","type":"finder","value":"Found in the hMailServer project's own security review (Progressive Robot Ltd)"}],"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."}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":7.5,"baseSeverity":"HIGH","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-407","description":"CWE-407: Inefficient Algorithmic Complexity","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-10-08T11:46:56.083Z","orgId":"ceab7361-8a18-47b1-92ba-4d7d25f6715a","shortName":"GitLab"},"references":[{"url":"https://gitlab.com/hmailserver/hmailserver/-/work_items/73"},{"url":"https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6"}],"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."}],"title":"Inefficient Algorithmic Complexity in hMailServer"}},"cveMetadata":{"assignerOrgId":"ceab7361-8a18-47b1-92ba-4d7d25f6715a","assignerShortName":"GitLab","cveId":"CVE-2026-107576","datePublished":"2026-10-08T11:46:56.083Z","dateReserved":"2026-10-08T10:51:45.640Z","dateUpdated":"2026-10-08T11:46:56.083Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-10-08 12:17:15","lastModifiedDate":"2026-10-08 12:17:15","problem_types":["CWE-407","CWE-407 CWE-407: Inefficient Algorithmic Complexity"],"metrics":{"cvssMetricV31":[{"source":"cve@gitlab.com","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}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"107576","Ordinal":"1","Title":"Inefficient Algorithmic Complexity in hMailServer","CVE":"CVE-2026-107576","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"107576","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Inefficient Algorithmic Complexity in hMailServer"}]}}}