XSS in Mapserver

CVE-2026-54355

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.

Vulnerability class: XSS (Cross-Site Scripting)

Published · last modified .

EPSS exploit prediction

EPSS: 0.005 (42.9th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 43rd percentile — 42.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-54355: held from 0.005 to 0.005.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

Weakness classification (CWE)

References