CVE-2026-104660 Missing Authorization in hMailServer
Local users can exploit missing COM authorization in hMailServer to read/write arbitrary files and execute code as SYSTEM.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-104660?
CVE-2026-104660 is a high-severity missing authorization vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Weakness: CWE-862
Which versions are affected by CVE-2026-104660?
How do I fix CVE-2026-104660?
No fix has been published for CVE-2026-104660 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-104660 being exploited?
There is no known exploitation of CVE-2026-104660 in the wild and no public exploit code.
Sources
Also known as GHSA-p223-vjjq-q36p.