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.
Advisories

No advisories yet.

Fixes

Solution

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).


Workaround

No workaround given by the vendor.

History

Wed, 21 Oct 2026 17:15:00 +0000

Type Values Removed Values Added
Description 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.
Title Incorrect Authorization in hMailServer
Weaknesses CWE-863
References
Metrics cvssV3_1

{'score': 5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N'}


Projects

Sign in to view the affected projects.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitLab

Published:

Updated: 2026-10-21T15:12:05.843Z

Reserved: 2026-10-21T15:11:15.857Z

Link: CVE-2026-114473

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-10-21T16:17:34.590

Modified: 2026-10-21T16:17:34.590

Link: CVE-2026-114473

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-21T21:00:11Z

Weaknesses