{"id":"CVE-2026-107576","summary":"Inefficient Algorithmic Complexity in hMailServer","details":"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.","modified":"2026-10-10T02:47:22.312841240Z","published":"2026-10-08T11:46:56.083Z","database_specific":{"cna_assigner":"GitLab","cwe_ids":["CWE-407"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107576.json"},"references":[{"type":"WEB","url":"https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6"},{"type":"WEB","url":"https://gitlab.com/hmailserver/hmailserver/-/work_items/73"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107576.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107576"},{"type":"PACKAGE","url":"https://gitlab.com/hmailserver/hmailserver"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://gitlab.com/hmailserver/hmailserver","events":[{"introduced":"e4b7163189ac6ce365bb954cf3e264e2e3105a18"},{"fixed":"e3c448aa66fc310b74d076884d54fae951296915"}],"database_specific":{"extracted_events":[{"introduced":"6.0.0"},{"fixed":"6.3.6"},{"fixed":"6.3.5"}],"source":["AFFECTED_FIELD","DESCRIPTION"]}}],"versions":["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-2026-107576.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}