CVE-2026-104660 Progressive Robot Ltd CVE debrief

Who should care

Defenders responsible for managing hMailServer installations should assess exposure and prioritize upgrading to version 6.3.6 or later. This includes IT teams, security teams, and system administrators who manage hMailServer deployments. They should review the CVE record and source item for details on the vulnerability and its impact.

Why it matters

Defenders should care about CVE-2026-104660 because it allows a local interactive user to exploit missing authorization in hMailServer, potentially leading to unauthorized file access and mail queuing.

• A local interactive user can read arbitrary files as the service account.
• A local interactive user can write arbitrary files as the service account.
• A local interactive user can queue mail as any sender.
• Verification of affected versions and remediation priority are required.

Technical summary

The vulnerability exists due to missing authorization on COM objects in Progressive Robot hMailServer 6.0.0 through 6.3.5, allowing a local interactive user to 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, making it vulnerable to exploitation. Defenders should prioritize verifying affected hMailServer installations and upgrading to version 6.3.6 or later.

Defensive priority

Defenders should prioritize verifying affected hMailServer installations and upgrading to version 6.3.6 or later.

Recommended defensive actions

• Verify hMailServer installations to determine if they are affected by CVE-2026-104660.
• Upgrade affected hMailServer installations to version 6.3.6 or later.
• Monitor hMailServer logs for suspicious activity.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record and source item provide details on the vulnerability, including its impact on hMailServer installations. The vulnerability was publicly disclosed on 2026-10-08T10:52:50.630Z. There are no known exploits in the wild, but defenders should verify affected versions and prioritize remediation. Evidence is limited to CVE Program and NVD details.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.