# CVE-2026-103647: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in hMailServer

> Remote attackers can execute scripts in the webmail origin via malicious encrypted attachments, potentially taking over user accounts.

- **Severity:** High 8.0 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 8 Oct 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-xr9h-mj6v-hm4m

## What is CVE-2026-103647?

CVE-2026-103647 is a high-severity cross-site scripting vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### 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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-103647?


## How do I fix CVE-2026-103647?

No fix has been published for CVE-2026-103647 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103647 being exploited?

There is no known exploitation of CVE-2026-103647 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103647 and fix it if it is affected.

What it is: CVE-2026-103647 is a high-severity cross-site scripting vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-103647 in the wild and no public exploit code.

Affected product: Progressive Robot Ltd hMailServer. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-103647/ (Markdown: https://insights.sbomify.com/CVE-2026-103647/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103647
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103647
- OSV: https://osv.dev/vulnerability/CVE-2026-103647

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103647/
Summaries are generated and may contain mistakes; the official description above is the record.