Vulnerability in Progressive Robot hMailServer Affecting Windows Users
CVE-2026-126621

7.5HIGH

Key Information:

Vendor

Progressive Robot Ltd

Status
Hmailserver
Vendor
CVE Published:
11 November 2026

What is CVE-2026-126621?

The hMailServer versions from 6.0.0-B1 through 6.3.7 on Windows are susceptible to a significant vulnerability allowing local attackers to exploit TLS configurations. By improperly handling the names of TLS-related files with non-ASCII characters, the server inadvertently lets attackers influence file access through misleading UTF-8 interpretations. This could lead to unauthorized access, interception of secure connections, and the potential compromise of sensitive stored messages and private keys. While the default configuration offers some safeguards—such as using ASCII for filenames and disabling client certificates—an attacker with sufficient permissions could manipulate the environment to exploit this vulnerability, stressing the importance of vigilance in server configurations.

Affected Version(s)

hMailServer 6.0.0-B1 <= 6.3.7

References

https://gitlab.com/hmailserver/hmailserver/-/work_items/115
https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.8

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
High
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Found by the hMailServer project (Progressive Robot Ltd)
.