Vulnerability · Published Oct 8, 2026 · Assigned by GitLab
CVE-2026-103647Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in hMailServer
High 8.0
In plain English
A high-severity cross-site scripting in hMailServer from Progressive Robot Ltd. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities).
Official 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.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Progressive Robot Ltd | hMailServer | 6.3.2 – before 6.3.6 |
Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N