CVE-2026-114474

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hMailServer External Account SPF/DMARC Bypass

Publication date: 2026-10-21

Last updated on: 2026-10-29

Assigner: GitLab Inc.

Description

Use of a less trusted source for the envelope sender in the external-account download of Progressive Robot hMailServer 6.0.0 through 6.3.6 allows a remote unauthenticated attacker to have mail they write in the name of a domain the server hosts sent on by the server with an envelope sender at that domain, so that it passes the domain's SPF and DMARC at other receivers. A message the server downloads from an external POP3 or IMAP account has no SMTP envelope of its own, and the server took the address in its From header as its envelope sender, whatever that address was. A forward or redirect of the downloaded message to an outside address then left with that address as its envelope sender, which the Sender Rewriting Scheme leaves alone for a hosted domain, so that the receiver's SPF check passed for the forged domain, aligned even under strict alignment, with no non-default setting, host name record or DMARC policy needed. An attacker needs to know a mailbox elsewhere that an account here collects and forwards to an outside address; an account holder who adds an external account of their own can collect from a server of their own, which matters where SmtpAuthenticatedSenderCheck holds signed-in senders to their own addresses.

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Meta Information

Published

2026-10-21

Last Modified

2026-10-29

Generated

2026-11-10

AI Q&A

2026-10-21

EPSS Evaluated

2026-11-09

NVD

CVE-2026-114474

EUVD

EUVD-2026-107317

Affected Vendors & Products

Vendor	Product	Version / Range
Progressive Robot Ltd	hMailServer	6.0.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-348	The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.

Attack-Flow Graph

Executive Summary

This vulnerability in hMailServer 6.0.0 through 6.3.6 allows attackers to send spoofed emails that bypass SPF and DMARC checks. When an external email is downloaded via POP3 or IMAP, the server uses the 'From' header as the envelope sender. If this email is then forwarded or redirected, the spoofed sender remains, tricking recipients into thinking the email is legitimate.

Detection Guidance

Check hMailServer logs for forwarded or redirected emails from external accounts with mismatched envelope senders. Look for messages where the SMTP envelope sender does not match the domain's SPF/DMARC policies. Use commands like 'grep' on mail logs to search for 'From' header addresses that differ from the envelope sender.

Impact Analysis

Attackers can send emails that appear to come from your domain, potentially tricking recipients into disclosing sensitive information or taking harmful actions. This could damage your domain's reputation and lead to phishing attacks being more successful.

Compliance Impact

This vulnerability could lead to unauthorized emails being sent from your domain, violating email authentication requirements in GDPR and HIPAA. It may result in non-compliance with data protection regulations due to potential data breaches or phishing incidents.

Mitigation Strategies

Disable forwarding or redirection of mail from external accounts until upgrading to hMailServer 6.3.7 or later. Review external account configurations to ensure no unauthorized forwarding rules exist. Monitor email logs for suspicious activity involving external mail sources.

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