---
id: "CVE-2026-114478"
kind: "vulnerability"
aliases: ["CVE-2026-114478"]
title: "hMailServer: forwarded mail can pass DMARC for a hosted domain"
severity: "medium"
cvss: 5.9
epss: 0.00261
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["dmarc", "email", "hmailserver", "package", "self-hosted"]
not_affected_if: ["envelope-rewrite-disabled", "no-forwarding", "srs-disabled"]
published_at: "2026-10-21T16:17:35+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-2026-114478", "first_seen_at": "2026-10-23T21:57:29+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-114478", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# hMailServer: forwarded mail can pass DMARC for a hosted domain

hMailServer 6.0.0 through 6.3.6 can send forwarded, redirected or list copies of outside mail with an envelope sender inside a hosted domain's organisation. Receivers then see the copy pass SPF and DMARC for that domain, so an unauthenticated sender can spoof it.

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

## How to check

- Check the hMailServer version (`6.3.6` and earlier are affected, 6.0.0 onward).
- Check whether Sender Rewriting Scheme or envelope sender rewriting on forwarding is enabled in the server settings.
- Check whether forwards, mail rules, Sieve redirects, or lists send mail from hosted domains to outside addresses.

## Fix

- Upgrade hMailServer to a release after `6.3.6` (the fixed version is not named in the sources; unknown).
- Until patched, leave Sender Rewriting Scheme and envelope sender rewriting disabled and review forwards and list bounce addresses.

## Timeline

- 2026-10-23T21:57:29+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-114478
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-114478

## From the sources

Insufficient preservation of the original sender in the forwarding of Progressive Robot hMailServer 6.0.0 through 6.3.6 allows a remote unauthenticated attacker to have mail they write, naming in its From an address at a domain the server hosts, delivered to other receivers as passing that domain's DMARC policy. When the server sent on a copy of mail that came from outside - an account's forward, a mail rule's forward, a Sieve redirect, a list's copy, or an alias or list expanding to an outside address - it could give the copy an SMTP identity in the organisation of the domain the copy's From names, whatever the message's origin: with the Sender Rewriting Scheme or the rewrite of the envelope sender on forwarding enabled (both off by default), an address at the forwarding domain; for a list, its bounce address; for a message with an empty envelope sender, none, under the server's own host name; and an envelope sender the message came with at a subdomain of a hosted domain was kept. Where that identity's SPF record authorises the server, other receivers' SPF check of the copy passed for a domain aligned with the From, and DMARC passed with it, although the message had not passed DMARC when the server received it. Exploitation needs a forward, redirect, alias or list that carries the hosted domain's mail to an outside address, and one of: SRS or the envelope rewrite enabled; a list whose bounce address is in the domain's organisation; an envelope sender at a subdomain whose SPF record authorises the server; or, for an empty envelope sender, an SPF record that authorises the server under its host name. The DKIM route to the same result is CVE-2026-107567.

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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_