CVE-2026-45104: OSGeo Mapserver

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

MapServer is a system for developing web-based GIS applications. From 6.4.0 to before 8.6.3, msSLDParseUserStyle always calls _SLDApplyRuleValues(psRule, psLayer, 1); for any <Rule> carrying <ElseFilter/> — it assumes msSLDParseRule added one class. When the rule has no symbolizer (a structurally valid SLD), msSLDParseRule adds zero, and _SLDApplyRuleValues ends up indexing _class[-1], resulting in a NULL pointer dereference. A 200-byte well-formed SLD via the WMS SLD_BODY= parameter is enough to trigger this, no auth required. This vulnerability is fixed in 8.6.3.

Affected products

• OSGeo Mapserver: from 6.4.0, before 8.6.3 (fixed in 8.6.3)

Published 2026-05-27. Last modified 2026-06-17.