Vulnerability · Published Mar 27, 2026 · Assigned by GitHub_M
CVE-2026-33721MapServer has heap buffer overflow in SLD `Categorize` Threshold parsing
Medium 5.3
In plain English
A medium-severity out-of-bounds write in MapServer from MapServer. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.2% (higher than 69% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | mapserver | 8.0.0-3+deb12u1 | DEBIAN-CVE-2026-33721 |
| Debian:13 | mapserver | 8.4.0-4+deb13u2 | DEBIAN-CVE-2026-33721 |
| Debian:14 | mapserver | 8.6.1-1 | DEBIAN-CVE-2026-33721 |
| Ubuntu:22.04:LTS | mapserver | no fix listed | UBUNTU-CVE-2026-33721 |
| Ubuntu:24.04:LTS | mapserver | no fix listed | UBUNTU-CVE-2026-33721 |
| Ubuntu:25.10 | mapserver | no fix listed | UBUNTU-CVE-2026-33721 |
| Ubuntu:26.04:LTS | mapserver | no fix listed | UBUNTU-CVE-2026-33721 |
| Ubuntu:26.10 | mapserver | no fix listed | UBUNTU-CVE-2026-33721 |
Affected products (as reported)
Weakness: CWE-787 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L