# CVE-2026-54355: mapserver: MapServer is a system for developing web-based GIS applications

CVE-2026-54355 is fixed in mapserver on 1 platform by DEBIAN-CVE-2026-54355 (version 8.6.4-1), released September 21, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-54355
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0050
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 17, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | mapserver Debian 14 | 8.6.4-1 | [DEBIAN-CVE-2026-54355](https://patchblox.com/security/data/fix/linux/debian-cve-2026-54355.md) | Sep 21, 2026 |

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Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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