CVE-2026-114472
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Denial of Service in hMailServer ACME HTTP-01 Challenge Responder
Vulnerability report for CVE-2026-114472, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-10-21
Last updated on: 2026-10-29
Assigner: GitLab Inc.
Description
Description
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.
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| Progressive Robot Ltd | hMailServer | 6.0.0 |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-410 | The product's resource pool is not large enough to handle peak demand, which allows an attacker to prevent others from accessing the resource by using a (relatively) large number of requests for resources. |
