Description
Missing Host header validation and missing throttling of failed administrator sign-ins in the REST API listener of Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote attacker to brute-force the server administrator's password through the administrator's own browser by DNS rebinding. The listener, which is off by default and bound to the loopback when enabled, answered requests whatever their Host header named, and a failed sign-in with the administrator's password from the loopback was neither auto-banned nor delayed. A web page whose host name the attacker rebinds to 127.0.0.1, opened in a browser on the server, can therefore send authenticated requests to the listener, read the answers and try administrator passwords at full speed until one is accepted, giving the attacker full administrative control of the mail server.
Published: 2026-10-08
Score: 7.5 High
EPSS: n/a
KEV: No
AI Analysis

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Remediation

Vendor Solution

Upgrade to hMailServer 6.3.6, whose REST listener refuses an unexpected Host before any authentication and delays a wrong administrator password on every route. Until then: keep the REST API off (RestApiPort 0, the default) or reach it only through a reverse proxy that checks the Host header; give the administrator a long random password and enrol its second factor; do not browse the web from the server.

Tracking

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Advisories

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History

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

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Thu, 08 Oct 2026 11:00:00 +0000

Type Values Removed Values Added
Description Missing Host header validation and missing throttling of failed administrator sign-ins in the REST API listener of Progressive Robot hMailServer 6.0.0 through 6.3.5 allow a remote attacker to brute-force the server administrator's password through the administrator's own browser by DNS rebinding. The listener, which is off by default and bound to the loopback when enabled, answered requests whatever their Host header named, and a failed sign-in with the administrator's password from the loopback was neither auto-banned nor delayed. A web page whose host name the attacker rebinds to 127.0.0.1, opened in a browser on the server, can therefore send authenticated requests to the listener, read the answers and try administrator passwords at full speed until one is accepted, giving the attacker full administrative control of the mail server.
Title Origin Validation Error in hMailServer
Weaknesses CWE-346
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H'}


Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitLab

Published:

Updated: 2026-10-08T14:24:55.631Z

Reserved: 2026-10-02T07:38:59.115Z

Link: CVE-2026-104659

cve-icon Vulnrichment

Updated: 2026-10-08T14:24:51.276Z

cve-icon NVD

Status : Received

Published: 2026-10-08T11:16:44.013

Modified: 2026-10-08T15:17:32.010

Link: CVE-2026-104659

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-08T12:45:18Z

Weaknesses