CVE-2026-104704

Cleartext Transmission of Sensitive Information in hMailServer

Published Oct 8, 2026 CVSS 3.1 · 7.4 High EPSS < 1% KEV · Not listed
Description
Progressive Robot hMailServer 6.0.0 through 6.3.5 does not enforce TLS for outbound SMTP delivery to a mail exchanger whose DNSSEC-validated TLSA records contain no DANE-EE (usage 3) record, contrary to RFC 7672 section 2.2. The server used only DANE-EE records and treated a validated TLSA record set consisting of DANE-TA (usage 2) or otherwise unusable records as if no records were published, so delivery to such a host fell back to opportunistic TLS. An attacker with an active position on the network path between the server and the recipient's mail exchanger can suppress or break the STARTTLS negotiation and cause messages to be delivered in cleartext, where they can be read and modified.

Remediation

Vendor Solution

Upgrade to hMailServer 6.3.6, which verifies DANE-TA as well as DANE-EE records and requires TLS to a host whose validated TLSA records are all unusable. Until then, an SMTP route for each recipient domain concerned that names its mail exchangers with the connection security 'STARTTLS (required)' prevents delivery in cleartext to that domain.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Progressive Robot
Progressive Robot hmailserver
Vendors & Products Progressive Robot
Progressive Robot hmailserver
Type Values Removed Values Added
Description Progressive Robot hMailServer 6.0.0 through 6.3.5 does not enforce TLS for outbound SMTP delivery to a mail exchanger whose DNSSEC-validated TLSA records contain no DANE-EE (usage 3) record, contrary to RFC 7672 section 2.2. The server used only DANE-EE records and treated a validated TLSA record set consisting of DANE-TA (usage 2) or otherwise unusable records as if no records were published, so delivery to such a host fell back to opportunistic TLS. An attacker with an active position on the network path between the server and the recipient's mail exchanger can suppress or break the STARTTLS negotiation and cause messages to be delivered in cleartext, where they can be read and modified.
Title Cleartext Transmission of Sensitive Information in hMailServer
Weaknesses CWE-319
References
Metrics cvssV3_1

{'score': 7.4, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitLab
Published
Updated
Oct 8, 2026, 2:25 PM
Reserved
Oct 2, 2026, 10:10 AM
Status
Deferred
Published
Oct 8, 2026, 11:16 AM
Modified
Oct 8, 2026, 9:02 PM