CVE-2026-104658
Received Received - Intake

Privilege Escalation in hMailServer Update Helper

Publication date: 2026-10-08

Last updated on: 2026-10-08

Assigner: GitLab Inc.

Description
The Linux live-update apply helper (hmailserver-update) of Progressive Robot hMailServer 6.3.4 and 6.3.5 runs as root on a request file written by the unprivileged hmailserver service account, and took from that request the program used to verify an AppImage update's signature and the systemd unit to stop before reading the service account's files. An attacker who already runs code as the hmailserver service account, for example through another flaw in the mail server, can therefore have arbitrary code executed as root, on any Linux installation where the live update's path unit is active - the default for the project's .deb and .rpm packages - and on AppImage installations run under that unit.

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Meta Information

Published
2026-10-08
Last Modified
2026-10-08
Generated
2026-10-08
AI Q&A
2026-10-08
EPSS Evaluated
N/A
NVD
CVE-2026-104658
EUVD
EUVD-2026-94832

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
Progressive Robot Ltd hMailServer 6.3.4

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-807 The product uses a protection mechanism that relies on the existence or values of an input, but the input can be modified by an untrusted actor in a way that bypasses the protection mechanism.

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Executive Summary

CVE-2026-104658 is a privilege escalation flaw in hMailServer versions 6.3.4 and 6.3.5 on Linux. The hmailserver-update helper runs as root and is triggered by a systemd unit when an update request is written by the unprivileged service account. An attacker with access to the service account can manipulate the update process to execute arbitrary code as root.

Detection Guidance

Check if the hmailserver-update.path unit is active by running: systemctl is-active hmailserver-update.path. If active, verify if the hmailserver service account has write access to /run/hmailserver where update requests are written.

Impact Analysis

If exploited, this vulnerability allows an attacker with limited access to gain full root privileges on the system. This could lead to complete system compromise, data theft, or further lateral movement within a network. Systems running affected versions with default configurations are at highest risk.

Compliance Impact

This vulnerability could lead to unauthorized root access, potentially violating data protection requirements under GDPR and HIPAA. Compromise of mail server systems may result in unauthorized access to sensitive data, triggering compliance violations and mandatory breach notifications.

Mitigation Strategies

Disable the hmailserver-update.path unit immediately by running: sudo systemctl disable --now hmailserver-update.path. Upgrade to hMailServer 6.3.6 or later via package manager. For AppImage users, manually update the helper script.

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