Inefficient Algorithmic Complexity in Progressive Robot hMailServer Product
CVE-2026-126623

7.5HIGH

Key Information:

Vendor

Progressive Robot Ltd

Status
Hmailserver
Vendor
CVE Published:
11 November 2026

What is CVE-2026-126623?

The JSON reader in hMailServer versions 6.3.6 and 6.3.7 can be exploited by a remote attacker, leading to potential service disruptions. The inefficient handling of JSON objects allows attackers to submit crafted TLS-RPT reports that, when processed, monopolize mail delivery threads or REST API worker threads. This results in significant delays or complete unavailability of mail services, impacting both local and outbound email communication. Malicious requests can bypass authentication requirements and affect system performance, making this an accessible vector for disruption against vulnerable installations.

Affected Version(s)

hMailServer 6.3.6 <= 6.3.7

References

https://gitlab.com/hmailserver/hmailserver/-/work_items/111
https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.8
https://www.cve.org/CVERecord?id=CVE-2026-107574

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
None
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)
.