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CVE-2026-103647: hMailServer

Severity

8 (HIGH)

Vendor

PROGRESSIVE ROBOT LTD

Affected versions

6.3.2 through before 6.3.6

Patch status

Unknown

Published

2026-10-08T11:16:42.950

Modified

2026-10-08T11:16:42.950

Why it matters

High-severity vulnerability requiring prioritized review.

Recommended admin actions

• Review and patch based on exposure, asset criticality, and business impact.
• Compare installed versions against the affected version range in the advisory.
• Treat internet-facing systems as higher priority.
• Review logs for suspicious activity related to the affected application or component.

Technical summary

Cross-site scripting in the webmail of Progressive Robot hMailServer 6.3.2 through 6.3.5 allows a remote attacker who can send a user an encrypted message to run script in the webmail's origin with that user's session. When the webmail decrypted an S/MIME message (from 6.3.2) or an OpenPGP message (from 6.3.4) in the browser, it offered each decrypted attachment as a blob URL of the media type the message declared for it. A click saved the file, but if the user opened the attachment in a new tab, a part declared as text/html was rendered as a document of the webmail's origin and its script could read the mailbox, send mail and change the account through the REST API. The webmail is served only when the REST API is enabled, which it is not by default.

View the official NVD record for CVE-2026-103647

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.