---
title: "CVE-2026-103647: Progressive Robot hMailServer - Stored XSS"
description: "Progressive Robot hMailServer 6.3.2 through 6.3.5 contains a stored XSS caused by unsafe rendering of decrypted S/MIME or OpenPGP message attachments as blob URLs in webmail, letting remote attackers execute scripts in the user's session, exploit requires REST API enabled."
url: https://panop.io/threat-heartbeat/CVE-2026-103647/
---

# CVE-2026-103647 Progressive Robot hMailServer - Stored XSS

Progressive Robot hMailServer 6.3.2 through 6.3.5 contains a stored XSS caused by unsafe rendering of decrypted S/MIME or OpenPGP message attachments as blob URLs in webmail, letting remote attackers execute scripts in the user's session, exploit requires REST API enabled.

CVSS base score 8.0 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.25% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-103647)

## Details

Type

Stored XSS

Impact

Stored XSS, Information Disclosure, Data Tampering

CVSS vector

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

Published

8 October 2026

Updated

15 October 2026

Weakness

[CWE-79](https://cwe.mitre.org/data/definitions/79.html)

## Vendor fix

Update to a version later than 6.3.5 or apply vendor patches.

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-2026-103647](https://nvd.nist.gov/vuln/detail/CVE-2026-103647)
- [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/52](https://gitlab.com/hmailserver/hmailserver/-/work_items/52)

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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

Panop answers these inside your environment, for this CVE and every other finding.

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