# CVE-2026-104659: Origin Validation Error in hMailServer

> Remote attackers can brute-force admin passwords via DNS rebinding due to missing host validation and throttling, gaining full administrative control.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 8 Oct 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-7264-4fp3-6f67

## What is CVE-2026-104659?

CVE-2026-104659 is a high-severity authentication bypass vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Missing Host header validation and missing throttling of failed administrator sign-ins in the REST API listener of Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote attacker to brute-force the server administrator's password through the administrator's own browser by DNS rebinding. The listener, which is off by default and bound to the loopback when enabled, answered requests whatever their Host header named, and a failed sign-in with the administrator's password from the loopback was neither auto-banned nor delayed. A web page whose host name the attacker rebinds to 127.0.0.1, opened in a browser on the server, can therefore send authenticated requests to the listener, read the answers and try administrator passwords at full speed until one is accepted, giving the attacker full administrative control of the mail server.

Weakness: CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-104659?


## How do I fix CVE-2026-104659?

No fix has been published for CVE-2026-104659 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-104659 being exploited?

There is no known exploitation of CVE-2026-104659 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-104659 and fix it if it is affected.

What it is: CVE-2026-104659 is a high-severity authentication bypass vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-104659 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-2026-104659/ (Markdown: https://insights.sbomify.com/CVE-2026-104659/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-104659
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-104659
- OSV: https://osv.dev/vulnerability/CVE-2026-104659

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-104659/
Summaries are generated and may contain mistakes; the official description above is the record.