Progressive Robot hMailServer up to 6.3.5 SPF Macro Expansion resource consumption

Summaryinfo

A vulnerability was found in Progressive Robot hMailServer up to 6.3.5 and classified as problematic. Affected by this issue is some unknown functionality of the component SPF Macro Expansion. Such manipulation leads to resource consumption. This vulnerability is listed as CVE-2026-107575. The attack may be performed from remote. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in Progressive Robot hMailServer up to 6.3.5 and classified as problematic. Affected by this issue is an unknown code of the component SPF Macro Expansion. The manipulation with an unknown input leads to a resource consumption vulnerability. Using CWE to declare the problem leads to CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. Impacted is availability. CVE summarizes:

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.

The advisory is shared for download at gitlab.com. This vulnerability is handled as CVE-2026-107575 since 10/08/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 6.3.6 eliminates this vulnerability.

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Productinfo

Type

• Mail Server Software

Vendor

• Progressive Robot

Name

• hMailServer

Version

• 6.3.0
• 6.3.1
• 6.3.2
• 6.3.3
• 6.3.4
• 6.3.5

CPE 2.3info

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CPE 2.2info

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