{"id":"CVE-2026-107576","title":"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 messag…","summary":"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 messag…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-407"],"vendor":"Progressive Robot Ltd","product":"hMailServer","affected":["hMailServer >= 6.0.0 < 6.3.6"],"published":"2026-10-08","updated":"2026-10-08","sourceUpdated":"2026-10-08T15:17:43.817","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-107576","references":[{"url":"https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6","label":"cve@gitlab.com"},{"url":"https://gitlab.com/hmailserver/hmailserver/-/work_items/73","label":"cve@gitlab.com"}],"tags":["nvd","cve.org"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-08T14:14:51.935522Z"},"ingestedAt":"2026-10-08T12:39:48.755Z","slug":"CVE-2026-107576","body":"## Overview\n\nInefficient 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}