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

> An attacker can downgrade SMTP connections to cleartext by exploiting DANE validation flaws, allowing interception and modification of email messages.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Oct 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-gv77-q2r2-h9qj

## What is CVE-2026-104704?

CVE-2026-104704 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 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.

Weakness: CWE-319 (Cleartext Transmission of Sensitive Information)

## Which versions are affected by CVE-2026-104704?


## How do I fix CVE-2026-104704?

No fix has been published for CVE-2026-104704 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-104704 being exploited?

There is no known exploitation of CVE-2026-104704 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-104704 and fix it if it is affected.

What it is: CVE-2026-104704 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.
Exploitation: There is no known exploitation of CVE-2026-104704 in the wild and no public exploit code.

Affected product: Progressive Robot Ltd hMailServer. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-104704/ (Markdown: https://insights.sbomify.com/CVE-2026-104704/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-104704
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-104704
- OSV: https://osv.dev/vulnerability/CVE-2026-104704

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-104704/
Summaries are generated and may contain mistakes; the official description above is the record.