Vulnerability in DKIM Signing Mechanism of Progressive Robot hMailServer
CVE-2026-107567

7.5HIGH

Key Information:

Vendor

Progressive Robot Ltd

Status
Hmailserver
Vendor
CVE Published:
19 October 2026

What is CVE-2026-107567?

The vulnerability in the DKIM signing mechanism of Progressive Robot hMailServer versions 6.0.0 through 6.3.6 allows remote unauthenticated attackers to forge emails. An attacker can exploit this flaw by sending email messages that appear to originate from a legitimate domain hosted by the server. The vulnerability results from the server signing messages without validating the sender's authenticity, enabling the attacker to use the valid DKIM key of any domain hosted by hMailServer. This leads to a risk of email forgery, as signed emails can bypass DMARC checks at receiving servers. The exploitation requires DKIM signing to be enabled for the domain, and allows for unauthorized emails to be forwarded or redirected to external addresses, potentially compromising email integrity and security.

Affected Version(s)

hMailServer 6.0.0 <= 6.3.6

References

https://gitlab.com/hmailserver/hmailserver/-/work_items/84
https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7

CVSS V3.1

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