# CVE-2026-107584: Not Failing Securely ('Failing Open') in hMailServer

> Attackers can bypass DANE security in hMailServer by manipulating DNS responses, causing emails to be delivered in cleartext or to malicious hosts.

- **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-m2j8-89fm-cxjh

## What is CVE-2026-107584?

CVE-2026-107584 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 fails open when applying DANE (RFC 7672) to outbound SMTP delivery. The server's validating DNSSEC resolver treated a TLSA or MX lookup that did not complete (no answer, SERVFAIL, a malformed reply), an answer without the requested records and without an NSEC/NSEC3 proof of their absence, and an answer whose records carried no applicable RRSIG as if the recipient domain were unsigned, and from 6.2.19 it also delivered to mail exchangers taken from an unvalidated MX lookup that the DNSSEC-validated MX record set did not name. An attacker who can drop, forge or strip DNS answers on the path to the server's resolver, at the resolver, or between the resolver and the recipient domain's name servers, and who holds an active position on the SMTP path, can thereby disable DANE for a DNSSEC-signed recipient domain and cause messages to be delivered in cleartext or to a host of the attacker's choosing with an arbitrary certificate, where they can be read and modified.

Weakness: CWE-636 (Not Failing Securely)

## Which versions are affected by CVE-2026-107584?


## How do I fix CVE-2026-107584?

No fix has been published for CVE-2026-107584 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-107584 being exploited?

There is no known exploitation of CVE-2026-107584 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-107584 and fix it if it is affected.

What it is: CVE-2026-107584 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-2026-107584 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-2026-107584/ (Markdown: https://insights.sbomify.com/CVE-2026-107584/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-107584
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-107584
- OSV: https://osv.dev/vulnerability/CVE-2026-107584

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-107584/
Summaries are generated and may contain mistakes; the official description above is the record.