---
id: "CVE-2026-114474"
kind: "vulnerability"
aliases: ["CVE-2026-114474"]
title: "hMailServer: forged From header lets forwarded mail pass SPF and DMARC"
severity: "medium"
cvss: 5.9
epss: 0.00164
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["email", "hmailserver", "mail-forwarding", "package", "self-hosted"]
not_affected_if: ["no-external-account-download", "no-outbound-forwarding", "patched-version"]
published_at: "2026-10-21T16:17:34+00:00"
first_seen_at: "2026-10-23T21:57:29+00:00"
updated_at: "2026-10-25T04:08:05+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-114474", "first_seen_at": "2026-10-23T21:57:29+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-114474", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# hMailServer: forged From header lets forwarded mail pass SPF and DMARC

hMailServer 6.0.0 through 6.3.6 takes the From header of mail downloaded from an external POP3 or IMAP account as its SMTP envelope sender. When that mail is forwarded to an outside address, the forged domain's SPF and DMARC checks pass at the receiver, so an attacker can send mail that appears to come from a hosted domain.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed hMailServer version; affected releases are `6.0.0` through `6.3.6`.
- Look for accounts that collect external mail (Fetch Accounts / external account download) and forward or redirect it to outside addresses.
- Check whether `SmtpAuthenticatedSenderCheck` is enabled.

## Fix

- Upgrade hMailServer to a release later than `6.3.6`; unknown which exact version contains the fix.
- Disable external account download and forwarding to outside addresses until patched, if feasible.

## Timeline

- 2026-10-23T21:57:29+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-114474
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-114474

## From the sources

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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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_