CVE-2026-104704 Details
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.
A vulnerability exists in Progressive Robot hMailServer versions 6.0.0 through 6.3.5, where the server fails to properly enforce TLS for outbound SMTP delivery to mail exchangers with DNSSEC-validated TLSA records lacking DANE-EE (usage 3) records. This oversight contradicts RFC 7672 section 2.2. The server only utilized DANE-EE records and disregarded validated TLSA record sets containing only DANE-TA (usage 2) or otherwise unusable records, treating them as if no records were published. Consequently, delivery to such hosts reverted to opportunistic TLS. An attacker with an active position on the network path can intercept or disrupt the STARTTLS negotiation, causing messages to be delivered in cleartext, where they can be read and modified.
Users are advised to upgrade to hMailServer version 6.3.6. Instructions for upgrading are available in the release notes.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Oct 8, 2026CISA-ADP
Assessed Oct 8, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6 | [email protected] | Release NotesVendor |
| https://gitlab.com/hmailserver/hmailserver/-/work_items/61 | [email protected] | ExploitIssue TrackingRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-319 | Cleartext Transmission of Sensitive Information | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Progressive Robot hMailServer | >= 6.0.0, <= 6.3.5 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Oct 8, 2026 | CVE Modified | CISA-ADP |
| Oct 8, 2026 | New CVE Received | [email protected] |