# CVE-2026-54355: MapServer: Reflected XSS in OpenLayers HTML Output via `HTTP_X_FORWARDED_HOST`

> An attacker can execute arbitrary JavaScript in MapServer's OpenLayers output via the X-Forwarded-Host header if specific resource configurations are not set.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:H/SI:H/SA: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:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 24 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-54355, GHSA-xqj6-vjqr-33vv, UBUNTU-CVE-2026-54355

## What is CVE-2026-54355?

CVE-2026-54355 is a medium-severity cross-site scripting vulnerability in MapServer, published on 17 Sep 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

MapServer is a system for developing web-based GIS applications. From 6.0 until 8.6.4, MapServer's OpenLayers HTML output for SERVICE=WMS&REQUEST=GetMap&FORMAT=application/openlayers reflects an attacker-controlled X-Forwarded-Host value received as HTTP_X_FORWARDED_HOST through msBuildOnlineResource(), processLine(), and the [mapserv_onlineresource] substitution in src/maputil.c and src/maptemplate.c without escaping it for a single-quoted JavaScript string. When the deployment trusts the forwarded header and does not configure a fixed ows_onlineresource or MS_ONLINERESOURCE value, embedded single quotes can escape the generated URL string. An unauthenticated attacker can craft a URL that executes arbitrary JavaScript in the MapServer site origin when opened by a victim, enabling access to sessions or tokens, same-origin data and requests, and actions as the victim. This issue is fixed in version 8.6.4.

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

## Which versions are affected by CVE-2026-54355?


## How do I fix CVE-2026-54355?

Upgrade to a fixed version.

## Is CVE-2026-54355 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54355 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54355 and fix it if it is affected.

What it is: CVE-2026-54355 is a medium-severity cross-site scripting vulnerability in MapServer, published on 17 Sep 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54355 exists.

Affected product: MapServer. 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-2026-54355/ (Markdown: https://insights.sbomify.com/CVE-2026-54355/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54355
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54355
- OSV: https://osv.dev/vulnerability/CVE-2026-54355

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-54355/
Summaries are generated and may contain mistakes; the official description above is the record.