Inefficient algorithmic complexity in the SPF macro expansion of Progressive Robot hMailServer 6.3.4 and 6.3.5 allows a remote unauthenticated attacker to consume worker-thread time by publishing a crafted SPF record. RFC 7208 section 7.1 requires a name too long to look up to lose whole labels from the left; the server did this by removing one label at a time and copying the rest of the name each time, so the work grew with the square of the expansion. An attacker who publishes an SPF record for a domain they control, with a mechanism whose domain-spec expands through macros to a name far longer than 253 characters, makes the SPF check of a message from that domain take several seconds. The expansion is bounded by SPF's own per-term and per-macro limits, so the loss of availability is partial.
Advisories

No advisories yet.

Fixes

Solution

Upgrade to hMailServer 6.3.6, which finds where the name becomes short enough and cuts it once. Until then, turn SPF checking off, or accept the bounded delay.


Workaround

No workaround given by the vendor.

History

Thu, 08 Oct 2026 15:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 08 Oct 2026 13:30:00 +0000

Type Values Removed Values Added
First Time appeared Progressive Robot
Progressive Robot hmailserver
Vendors & Products Progressive Robot
Progressive Robot hmailserver

Thu, 08 Oct 2026 12:00:00 +0000

Type Values Removed Values Added
Description Inefficient algorithmic complexity in the SPF macro expansion of Progressive Robot hMailServer 6.3.4 and 6.3.5 allows a remote unauthenticated attacker to consume worker-thread time by publishing a crafted SPF record. RFC 7208 section 7.1 requires a name too long to look up to lose whole labels from the left; the server did this by removing one label at a time and copying the rest of the name each time, so the work grew with the square of the expansion. An attacker who publishes an SPF record for a domain they control, with a mechanism whose domain-spec expands through macros to a name far longer than 253 characters, makes the SPF check of a message from that domain take several seconds. The expansion is bounded by SPF's own per-term and per-macro limits, so the loss of availability is partial.
Title Inefficient Algorithmic Complexity in hMailServer
Weaknesses CWE-407
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}


Projects

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitLab

Published:

Updated: 2026-10-08T14:17:04.989Z

Reserved: 2026-10-08T10:51:40.639Z

Link: CVE-2026-107575

cve-icon Vulnrichment

Updated: 2026-10-08T14:17:00.390Z

cve-icon NVD

Status : Received

Published: 2026-10-08T12:17:15.333

Modified: 2026-10-08T15:17:43.697

Link: CVE-2026-107575

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-08T14:30:18Z

Weaknesses