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Fencer Vulns
medium 5.3

CVE-2026-33721 json

MapServer has heap buffer overflow in SLD `Categorize` Threshold parsing

published 2026-03-27 7 mo ago modified 2026-06-17 4 mo ago also EUVD-2026-16501

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 68%
public exploits
0
none known

Summary

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.

Patch / fix

  • osgeo mapserver 8.6.1
  • university_of_minnesota mapserver 8.6.1
  • mapserver Debian 12 8.0.0-3+deb12u1
  • mapserver Debian 13 8.4.0-4+deb13u2
  • mapserver Debian 14 8.6.1-1

debian advisories DEBIAN-CVE-2026-33721

  • mapserver openSUSE Leap 16.0 8.6.1-bp160.1.1
  • mapserver openSUSE Tumbleweed 8.6.1-1.1

opensuse advisories openSUSE-SU-2026:20476-1openSUSE-SU-2026:10452-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-33721 updated cvss 7.5

MapServer: MapServer: Denial of Service via crafted Styled Layer Descriptor

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

1.22% chance of exploitation in the next 30 days, higher than 68% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/MapServer/MapServer/security/advisories/GHSA-cv4m-mr84-fgjp referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • MapServer MapServer

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.