Vulnerability · Published Oct 8, 2026 · Assigned by GitLab
CVE-2026-107584Not Failing Securely ('Failing Open') in hMailServer
High 7.4
In plain English
A high-severity security flaw in hMailServer from Progressive Robot Ltd. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 4% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Progressive Robot Ltd | hMailServer | 6.0.0 – before 6.3.6 |
Weakness: CWE-636 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N