Inefficient Algorithmic Processing in Progressive Robot hMailServer
CVE-2026-107579

7.5HIGH

Key Information:

Vendor

Progressive Robot Ltd

Status
Hmailserver
Vendor
CVE Published:
8 October 2026

What is CVE-2026-107579?

A flaw in the bounce and complaint processing mechanisms of Progressive Robot hMailServer versions 6.3.4 and 6.3.5 introduces inefficiencies that allow remote attackers to interfere with mail delivery. This vulnerability arises from an inefficient algorithm that processes delivery status notifications and abuse feedback reports. Attackers can exploit the system by sending specially crafted messages containing excessive blank lines, causing a significant delay in mail processing. As the number of blank lines increases, the time taken to process these messages escalates, effectively monopolizing server resources and halting email delivery under certain conditions.

Affected Version(s)

hMailServer 6.3.4 < 6.3.6

References

https://gitlab.com/hmailserver/hmailserver/-/work_items/70
https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6

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 in the hMailServer project's own security review (Progressive Robot Ltd)
.