Progressive Robot hMailServer up to 6.3.5 COM Objects path/AccountID improper authorization

Summaryinfo

A vulnerability identified as critical has been detected in Progressive Robot hMailServer up to 6.3.5. This vulnerability affects the function Attachments.Add/Attachment.SaveAs/Message.Save/Message.Copy/FetchAccount.Save of the component COM Objects. The manipulation of the argument path/AccountID leads to improper authorization. This vulnerability is traded as CVE-2026-104660. An attack has to be approached locally. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Progressive Robot hMailServer up to 6.3.5 and classified as critical. This issue affects the function Attachments.Add/Attachment.SaveAs/Message.Save/Message.Copy/FetchAccount.Save of the component COM Objects. The manipulation of the argument path/AccountID with an unknown input leads to a improper authorization vulnerability. Using CWE to declare the problem leads to CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Missing authorization on COM objects in Progressive Robot hMailServer 6.0.0 through 6.3.5 (Windows only) lets a local interactive user with no hMailServer credential read and write arbitrary files as the service account and queue mail as any sender. The service registers its COM classes with no DCOM access or launch permission and calls CoInitializeSecurity with no security descriptor, so any user logged on at the console or over Remote Desktop can activate the classes in the running service; a hMailServer.Message, its Attachments and Attachment, and a hMailServer.FetchAccount created this way carry a credential that never authenticated. Attachments.Add(path) and Attachment.SaveAs(path) performed no authorization check, and Message.Save/Copy and FetchAccount.AccountID/Save performed none either up to 6.3.3 and from 6.3.4 treated a holder with no credential as the server's own event-script host. Because the service does not impersonate the COM caller, Attachments.Add reads any file the service account can read and returns it, Attachment.SaveAs writes attacker-chosen bytes to any path it can write (on a LocalSystem installation, code execution as SYSTEM), Message.Save queues outbound mail from any address past the SMTP checks, and FetchAccount attaches a mail-fetch job to any mailbox. The objects an Application handed out behave the same once a later Authenticate on that Application fails.

It is possible to read the advisory at gitlab.com. The identification of this vulnerability is CVE-2026-104660 since 10/02/2026. The exploitation is known to be easy. Attacking locally is a requirement. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1548.002 according to MITRE ATT&CK.

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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