---
id: CVE-2026-114473
title: Incorrect Authorization in hMailServer
summary: >-
  Incorrect authorization in the Sender Rewriting Scheme (SRS) of Progressive
  Robot hMailServer 6.2.1 through 6.3.6 allows a remote attacker to relay mail
  through the server to outside addresses. With SRS enabled, the server rewrites
  the e…
severity: medium
cvss: 5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N'
cvssSource: cna
cwe:
  - CWE-863
vendor: Progressive Robot Ltd
product: hMailServer
affected:
  - hMailServer >= 6.2.1 <= 6.3.6
published: '2026-10-21'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T15:12:05.843Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-114473'
references:
  - url: 'https://gitlab.com/hmailserver/hmailserver/-/work_items/94'
  - url: 'https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7'
tags:
  - cve.org
ingestedAt: '2026-10-21T16:05:17.709Z'
---

## Overview

Incorrect authorization in the Sender Rewriting Scheme (SRS) of Progressive Robot hMailServer 6.2.1 through 6.3.6 allows a remote attacker to relay mail through the server to outside addresses. With SRS enabled, the server rewrites the envelope sender of mail it forwards to a signed SRS address at the forwarding domain, and passes a bounce to that address back to the original sender; but it took every message to a valid SRS address, whatever its sender, as delivery to a local recipient, so the relay rules and the SMTP authentication they require were not applied, and the message was delivered to the outside address the SRS address encodes. Anyone holding a valid SRS address of the server, such as the recipient of a forwarded message, could have the server relay mail to the address it encodes for 21 days, and an account holder whose account forwards to an outside mailbox could obtain one for any address. SRS is off by default.

## Affected

- `hMailServer >= 6.2.1 <= 6.3.6`

## Remediation

Upgrade to hMailServer 6.3.7, which takes only a bounce (a null reverse-path) to an SRS address as local delivery and holds any other message to it to the relay rules: where they refuse it, the transaction is refused at DATA or BDAT, and a recipient named after such an address in the same transaction is answered 452 4.5.3. Until then, turn SRS off (SRSEnabled=0, the default).