Progressive Robot hMailServer up to 6.3.6 ACME HTTP-01 challenge responder resource consumption

Summaryinfo

A vulnerability was found in Progressive Robot hMailServer up to 6.3.6 and classified as problematic. The affected element is an unknown function of the component ACME HTTP-01 challenge responder. The manipulation results in resource consumption. This vulnerability was named CVE-2026-114472. The attack may be performed from remote. There is no available exploit. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Progressive Robot hMailServer up to 6.3.6. Affected is an unknown code of the component ACME HTTP-01 challenge responder. The manipulation with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as 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. This is going to have an impact on availability. CVE summarizes:

Insufficient resource pool in the ACME HTTP-01 challenge responder of Progressive Robot hMailServer 6.0.0 through 6.3.6 allows a remote unauthenticated attacker to cause a certificate issuance or renewal to fail. When the server obtains or renews a TLS certificate over ACME it runs an HTTP-01 challenge responder on port 80 for the certificate authority to read the challenge token; the responder served one connection at a time, accepting a socket, waiting up to five seconds to receive a request, answering it, and only then accepting the next. A client that connected and sent nothing held the single worker for the whole timeout, so enough idle connections during a validation keep the certificate authority's own request from being answered in time and the validation fails. Sustained across a certificate's renewals this leads to the certificate expiring, after which clients refuse the server's TLS; the mail service itself continues on its current certificate until then. No authentication is required to connect to the responder. Version 6.3.7 serves up to 64 connections at once and closes a connection past that, so that where a handful of idle connections, one after another, sufficed before, a client must keep 64 idle connections open at once throughout a validation to have the certificate authority's connection closed.

The advisory is shared for download at gitlab.com. This vulnerability is traded as CVE-2026-114472 since 10/21/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 6.3.7 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
• 6.3.6

CPE 2.3info

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CPE 2.2info

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