How severe is CVE-2026-33721?

CVE-2026-33721 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2026-33721 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33721?

CVE-2026-33721 affects Osgeo Mapserver. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33721?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-33721 have an EU (EUVD) identifier?

Yes. CVE-2026-33721 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16501.

When was CVE-2026-33721 published?

CVE-2026-33721 was published on 2026-03-27 and last updated on 2026-06-17.

CVE-2026-33721

CVE-2026-33721 is a medium-severity vulnerability in Osgeo Mapserver with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16501
Weakness: CWE-787
Affected product: Osgeo Mapserver
Published: 2026-03-27
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-33721?: CVE-2026-33721 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2026-33721 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33721?: CVE-2026-33721 affects Osgeo Mapserver. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33721?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33721 have an EU (EUVD) identifier?: Yes. CVE-2026-33721 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16501.
When was CVE-2026-33721 published?: CVE-2026-33721 was published on 2026-03-27 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:osgeo:mapserver:*:*:*:*:*:*:*:*

More vulnerabilities in Osgeo Mapserver

CVE-2010-2540 — Critical (CVSS 10.0): mapserv.c in mapserv in MapServer before 4.10.6 and 5.x before 5.6.4 does not properly restrict the use of CGI…
CVE-2009-2281 — Critical (CVSS 10.0): Multiple heap-based buffer underflows in the readPostBody function in cgiutil.c in mapserv in MapServer 4.x through…
CVE-2009-1177 — Critical (CVSS 10.0): Multiple stack-based buffer overflows in maptemplate.c in mapserv in MapServer 4.x before 4.10.4 and 5.x before 5.2.2…
CVE-2009-1176 — Critical (CVSS 10.0): mapserv.c in mapserv in MapServer 4.x before 4.10.4 and 5.x before 5.2.2 does not ensure that the string holding the id…
CVE-2009-0841 — Critical (CVSS 10.0): Directory traversal vulnerability in mapserv.c in mapserv in MapServer 4.x before 4.10.4 and 5.x before 5.2.2, when…
CVE-2009-0840 — Critical (CVSS 10.0): Heap-based buffer underflow in the readPostBody function in cgiutil.c in mapserv in MapServer 4.x before 4.10.4 and 5.x…

All CVEs affecting Osgeo Mapserver →

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