Memory Exhaustion Vulnerability in hMailServer by Progressive Robot
CVE-2026-126613

7.5HIGH

Key Information:

Vendor

Progressive Robot Ltd

Status
Hmailserver
Vendor
CVE Published:
11 November 2026

What is CVE-2026-126613?

A flaw in the JSON reader of hMailServer versions 6.3.2 through 6.3.7 permits a remote attacker to exploit resource allocation without limits. By sending a specially crafted JSON document via a TLS-RPT report or through specific routes in webmail, an attacker can consume excessive memory, keeping threads busy and causing mail delivery, REST API functions, and webmail access to fail. This vulnerability can lead to service outages and degrade overall server performance, making it critical for administrators to review and mitigate the associated risks.

Affected Version(s)

hMailServer 6.3.2 <= 6.3.7

References

https://gitlab.com/hmailserver/hmailserver/-/work_items/110
https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.8

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)
.