Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in hMailServer

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-103647
StatePUBLISHED
AssignerGitLab
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-08 11:16:42 UTC
Updated2026-10-08 11:16:42 UTC
DescriptionCross-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.

Risk And Classification

Primary CVSS: v3.1 8 HIGH from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

Problem Types: CWE-79 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N
3.1CNACVSS8HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Progressive Robot Ltd HMailServer affected 6.3.2 6.3.6 semver Not specified

References

ReferenceSourceLinkTags
gitlab.com/hmailserver/hmailserver/-/releases/v6.3.6 [email protected] gitlab.com
gitlab.com/hmailserver/hmailserver/-/work_items/52 [email protected] gitlab.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Found in the hMailServer project's own security review (Progressive Robot Ltd) (en)

Additional Advisory Data

Solutions

CNA: Upgrade to hMailServer 6.3.6, which hands every decrypted attachment to the browser as application/octet-stream so that it is only ever saved. Until then: keep the REST API off (RestApiPort 0, the default), or tell webmail users not to open decrypted attachments in a new tab.

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