{"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":"2026-10-08T14:15:09.064Z"},"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"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-08T14:14:51.935522Z","id":"CVE-2026-107576","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-10-08T14:15:09.064Z"}}]}}