CVE-2026-33721
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…
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.86%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.86% probability · 57th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-787
- Affected
- osgeo/mapserver
- Source
- security-advisories@github.com
References
- https://github.com/MapServer/MapServer/releases/tag/rel-8-6-1Product, Release Notes
- https://github.com/MapServer/MapServer/security/advisories/GHSA-cv4m-mr84-fgjpExploit, Mitigation, Vendor Advisory
- https://lists.debian.org/debian-lts-announce/2026/04/msg00017.html
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.