CVE-2026-103647 Details
Description
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.
A cross-site scripting vulnerability has been identified in the webmail component of Progressive Robot hMailServer versions 6.3.2 through 6.3.5. This issue allows remote attackers to execute scripts in the context of the user's session by sending encrypted messages that, when decrypted, render certain types of content as active HTML. The vulnerability arises because the webmail application does not properly sanitize or handle decrypted attachments, particularly those containing HTML, before presenting them to the user.
Users are advised to upgrade to hMailServer version 6.3.6, which addresses this vulnerability by changing how decrypted attachments are handled. Instructions for upgrading are available in the release notes for version 6.3.6.
Metrics
CVSS 4.0 Severity and Vector Strings:
VolerionCVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
Volerion
Assessed Oct 8, 2026CISA-ADP
Assessed Oct 8, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6 | [email protected] | Release NotesVendor |
| https://gitlab.com/hmailserver/hmailserver/-/work_items/52 | [email protected] | ExploitIssue TrackingRemedyVendor |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-79 | Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| Progressive Robot hMailServer | 6.3.2 (semver) 6.3.3 (semver) 6.3.4 (semver) 6.3.5 (semver) |
CPE
Remediation
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Change History
2 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Oct 8, 2026 | CVE Modified | CISA-ADP |
| Oct 8, 2026 | New CVE Received | [email protected] |