Denial of Service Vulnerability in Progressive Robot hMailServer by hMailServer
CVE-2026-103649
7.5HIGH
What is CVE-2026-103649?
The Progressive Robot hMailServer versions 6.3.0 through 6.3.5 are exposed to a vulnerability that allows remote attackers to indefinitely hold server threads due to missing network timeouts, resulting in the disruption of outbound mail delivery. The Linux builds set socket timeouts in a manner inconsistent with Linux standards, leading to the potential for a malicious actor to manipulate connections, effectively preventing the server from delivering emails. This flaw extends to several components including the MTA-STS policy and others involved in outbound delivery, allowing exploitation by controlling domains that receive bounced messages.
Affected Version(s)
hMailServer 6.3.0 < 6.3.6
References
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 static-analysis review (Progressive Robot Ltd)