---
title: "CVE-2026-103649: Progressive Robot hMailServer - Denial of Service"
description: "Progressive Robot hMailServer 6.3.0 through 6.3.5 Linux builds contain a denial of service caused by missing network timeouts in socket handling, letting remote attackers hold server threads indefinitely, exploit requires sending crafted mail to trigger outbound delivery to attacker-controlled domains."
url: https://panop.io/threat-heartbeat/CVE-2026-103649/
---

# CVE-2026-103649 Progressive Robot hMailServer - Denial of Service

Progressive Robot hMailServer 6.3.0 through 6.3.5 Linux builds contain a denial of service caused by missing network timeouts in socket handling, letting remote attackers hold server threads indefinitely, exploit requires sending crafted mail to trigger outbound delivery to attacker-controlled domains.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.27% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-103649)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Published

8 October 2026

Updated

15 October 2026

Weakness

[CWE-1088](https://cwe.mitre.org/data/definitions/1088.html)

## Vendor fix

Update to a version later than 6.3.5 or the latest available version.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-103649](https://nvd.nist.gov/vuln/detail/CVE-2026-103649)
- [https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6](https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6)
- [https://gitlab.com/hmailserver/hmailserver/-/work\_items/53](https://gitlab.com/hmailserver/hmailserver/-/work_items/53)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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