CVE-2026-107584 Not Failing Securely ('Failing Open') in hMailServer
Attackers can bypass DANE security in hMailServer by manipulating DNS responses, causing emails to be delivered in cleartext or to malicious hosts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-107584?
CVE-2026-107584 is a high-severity vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-636
Which versions are affected by CVE-2026-107584?
How do I fix CVE-2026-107584?
No fix has been published for CVE-2026-107584 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-107584 being exploited?
There is no known exploitation of CVE-2026-107584 in the wild and no public exploit code.
Sources
Also known as GHSA-m2j8-89fm-cxjh.