CVE-2026-33721: OSGeo Mapserver

High severity, CVSS 7.5. EPSS: 0.8% chance of exploitation in the next 30 days.

MapServer is a system for developing web-based GIS applications. Starting in version 4.2 and prior to version 8.6.1, a heap-buffer-overflow write in MapServer’s SLD (Styled Layer Descriptor) parser lets a remote, unauthenticated attacker crash the MapServer process by sending a crafted SLD with more than 100 Threshold elements inside a ColorMap/Categorize structure (commonly reachable via WMS GetMap with SLD_BODY). Version 8.6.1 patches the issue.

Affected products

• OSGeo Mapserver: from 4.2.0, before 8.6.1 (fixed in 8.6.1)

Published 2026-03-27. Last modified 2026-06-17.