Is CVE-2026-33721 in the CISA KEV catalog?

No. CVE-2026-33721 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-33721?

CVE-2026-33721 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-33721?

CVE-2026-33721 has an EPSS score of 0.86% (54th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-33721?

Upgrade mapserver on debian 11 to 7.6.2-1+deb11u2 or later.

CVE & CISA-KEV Catalog

CVE-2026-33721

MEDIUM

5.3

CVSS v3

NVD

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.

CWE-787Out-of-bounds Write

How to fix

Remediation Available

mapserverDebian

Fixed in:7.6.2-1+deb11u2CVE-2026-33721

Fixed in:8.0.0-3+deb12u1CVE-2026-33721

Fixed in:8.4.0-4+deb13u2CVE-2026-33721

Fixed in:8.6.1-1CVE-2026-33721

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Exploit Intelligence

0.86%probability of exploitation in 30 days

54thpercentile

Moderate risk: more likely to be exploited than 54% of all known CVEs.

References

Exploit1

github.com

Release Notes1

github.com

Other references1

lists.debian.org

Related Vulnerabilities

Other CWE-787 (Out-of-bounds Write) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2025-22457	Critical	9.0	100%	KEV + Ransom	Fix
CVE-2025-0282	Critical	9.0	100%	KEV + Ransom	-
CVE-2015-3113	Critical	9.8	100%	KEV	Fix
CVE-2021-20038	Critical	9.8	100%	KEV + Ransom	-
CVE-2023-4863	High	8.8	100%	KEV	Fix
CVE-2020-16040	Medium	6.5	100%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-17.