Buffer overflow in Mapserver
CVE-2026-33721
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.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.008 (55.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 55.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.009 · newest: 0.008 · change: -0.000
Affected products
- Mapserver — versions >= 4.2, < 8.6.1
- Osgeo Mapserver
Weakness classification (CWE)
References
- github.com/MapServer/MapServer/security/advisories/GHSA-cv4m-mr84-fgjp (Exploit, Mitigation, Vendor Advisory)
- github.com/MapServer/MapServer/releases/tag/rel-8-6-1 (Product, Release Notes)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2026-33721?
- CVE-2026-33721 is a medium-severity vulnerability in Mapserver, classified under Out-of-bounds Write. CVSS score: 5.3/10. Published 2026-03-27.
- How severe is CVE-2026-33721?
- Medium severity. CVSS v3 base score is 5.3 out of 10.