---
id: CVE-2026-107584
title: >-
  Progressive Robot hMailServer 6.0.0 through 6.3.5 fails open when applying
  DANE (RFC 7672) to outbound SMTP delivery
summary: >-
  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 malfo…
severity: high
cvss: 7.4
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N'
cwe:
  - CWE-636
vendor: Progressive Robot Ltd
product: hMailServer
affected:
  - hMailServer >= 6.0.0 < 6.3.6
published: '2026-10-08'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T12:17:16.787'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-107584'
references:
  - url: 'https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6'
    label: cve@gitlab.com
  - url: 'https://gitlab.com/hmailserver/hmailserver/-/work_items/64'
    label: cve@gitlab.com
tags:
  - nvd
  - cve.org
ingestedAt: '2026-10-08T12:39:48.758Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.