hMailServer: Cleartext Transmission of Sensitive Information
CVE-2026-104704 is a high-severity cleartext transmission of sensitive information vulnerability in hMailServer from Progressive Robot, with a CVSS 3.1 base score of 7.4 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 6.3.6 as the first without the flaw, so updating hMailServer to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.15% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update hMailServer to 6.3.6 or a later version.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Progressive Robot | hMailServer | 6.0.0 up to, but not including, 6.3.6 | 6.3.6 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by CNA (gitlab.com).
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Cleartext Transmission of Sensitive Information
The product transmits sensitive or security-critical data in cleartext in a communication channel that can be sniffed by unauthorized actors.
How developers prevent this class of flaw
- Before transmitting, encrypt the data using reliable, confidentiality-protecting cryptographic protocols.
- When using web applications with SSL, use SSL for the entire session from login to logout, not just for the initial login page.
- When designing hardware platforms, ensure that approved encryption algorithms (such as those recommended by NIST) protect paths from security critical data to trusted user applications.
More Cleartext Transmission of Sensitive Information vulnerabilities (CWE-319)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
References
Patches and release notes
Other references
Other vulnerabilities in hMailServer
- 7.3 High severity
- 7.5 High severity
- 7.3 High severity
- 7.5 High severity
- 8.8 High severity
- 7.5 High severity
Recent Cleartext Transmission of Sensitive Information vulnerabilities
- 9.4 Critical severity
- 7.5 High severity
- 8.7 High severity
- 7.5 High severity
- 7.3 High severity
- 8.5 High severity
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