Not Failing Securely ('Failing Open') in hMailServer
Summary
| CVE | CVE-2026-107584 |
|---|---|
| State | PUBLISHED |
| Assigner | GitLab |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-08 12:17:16 UTC |
| Updated | 2026-10-08 12:17:16 UTC |
| Description | Progressive Robot hMailServer 6.0.0 through 6.3.5 fails open when applying DANE (RFC 7672) to outbound SMTP delivery. The server's validating DNSSEC resolver treated a TLSA or MX lookup that did not complete (no answer, SERVFAIL, a malformed reply), an answer without the requested records and without an NSEC/NSEC3 proof of their absence, and an answer whose records carried no applicable RRSIG as if the recipient domain were unsigned, and from 6.2.19 it also delivered to mail exchangers taken from an unvalidated MX lookup that the DNSSEC-validated MX record set did not name. An attacker who can drop, forge or strip DNS answers on the path to the server's resolver, at the resolver, or between the resolver and the recipient domain's name servers, and who holds an active position on the SMTP path, can thereby disable DANE for a DNSSEC-signed recipient domain and cause messages to be delivered in cleartext or to a host of the attacker's choosing with an arbitrary certificate, where they can be read and modified. |
Risk And Classification
Primary CVSS: v3.1 7.4 HIGH from [email protected]
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Problem Types: CWE-636 | CWE-636 CWE-636: Not Failing Securely ('Failing Open')
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 7.4 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
| 3.1 | CNA | CVSS | 7.4 | HIGH | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
CVSS v3.1 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Progressive Robot Ltd | HMailServer | affected 6.0.0 6.3.6 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6 | [email protected] | gitlab.com | |
| gitlab.com/hmailserver/hmailserver/-/work_items/64 | [email protected] | gitlab.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Found in the hMailServer project's own security review (Progressive Robot Ltd) (en)
Additional Advisory Data
Solutions
CNA: Upgrade to hMailServer 6.3.6, which treats an incomplete, unsigned or unproven DNSSEC answer for a TLSA or MX lookup under a signed zone as indeterminate, does not use a mail exchanger whose lookup was indeterminate, defers the delivery when none is left, delivers only to mail exchangers named by a DNSSEC-validated MX record set, and (for a host whose DNS servers are IPv6 only) asks those IPv6 servers. Until then, for each recipient domain whose mail must be protected, an SMTP route that names its mail exchangers with the connection security 'STARTTLS (required)', with remote certificate verification on (VerifyRemoteSslCertificate=1), prevents delivery in cleartext or to another host for that domain; and the server's DNS resolver should be one reached over a trusted path, such as a validating resolver on the same host.