High severity · published Mar 27, 2026
CVE-2026-33721
MapServer has heap buffer overflow in SLD `Categorize` Threshold parsing
7.5
CVSS
1.2%
EPSS
No
On KEV
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)1.2% · higher than 69% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
MapServer · MapServer
>= 4.2, < 8.6.1 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33721
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-33721
Product
https://github.com/MapServer/MapServer/releases/tag/rel-8-6-1
Exploit
https://github.com/MapServer/MapServer/security/advisories/GHSA-cv4m-mr84-fgjp
lists.debian.org
https://lists.debian.org/debian-lts-announce/2026/04/msg00017.html
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