Vulnerability in hMailServer from Progressive Robot Allows Password Guessing
CVE-2026-126618

5.3MEDIUM

Key Information:

Vendor

Progressive Robot Ltd

Status
Hmailserver
Vendor
CVE Published:
11 November 2026

What is CVE-2026-126618?

The hMailServer versions from 6.0.0-B1 to 6.3.7 have a design flaw in their auto-ban feature that permits attackers to guess passwords without being banned. The vulnerability arises when failed login attempts from one IP address reach a set limit (three by default). While the server initiates an auto-ban mechanism, it can inadvertently allow an attacker using multiple IP addresses to bypass bans due to naming conflicts and character limitations in usernames. This allows attackers to keep guessing passwords across several services, including SMTP AUTH, IMAP, POP3, and web services, effectively undermining the security measures intended to protect user accounts.

Affected Version(s)

hMailServer 6.0.0-B1 <= 6.3.7

References

https://gitlab.com/hmailserver/hmailserver/-/work_items/102
https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.8

CVSS V3.1

Score:
5.3
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
None
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Found by the hMailServer project (Progressive Robot Ltd)
.