Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LSummary
CVE-2026-33721 is a medium-severity Out-of-bounds Write (CWE-787) vulnerability in Osgeo Mapserver. Its CVSS base score is 5.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked in the top 45% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-33721 is a heap-buffer-overflow write vulnerability in the Styled Layer Descriptor (SLD) parser of MapServer, an open-source system for developing web-based GIS applications. The flaw affects MapServer versions starting from 4.2 up to but not including 8.6.1. It stems from improper handling of SLD structures, specifically when processing more than 100 Threshold elements within a ColorMap or Categorize element, classified under CWE-787 (Out-of-bounds Write). The issue carries a CVSS v3.1 base score of 5.3 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L), indicating medium severity primarily due to availability impact.
A remote, unauthenticated attacker can exploit this vulnerability by sending a specially crafted SLD document to a vulnerable MapServer instance, commonly via a WMS GetMap request containing an SLD_BODY parameter. Successful exploitation triggers a heap buffer overflow during parsing, causing the MapServer process to crash and resulting in a denial-of-service condition. No user interaction is required, and the attack is straightforward given the low complexity and network accessibility.
Mitigation is available through upgrading to MapServer version 8.6.1 or later, which includes a patch for the SLD parser issue, as detailed in the official release notes. The MapServer security advisory (GHSA-cv4m-mr84-fgjp) confirms the fix and provides additional context on the vulnerability. Debian LTS users are also advised via announcement to apply relevant updates for affected packages.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-16501
Vulnerability Data
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…
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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(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation (including fuzzing and bounds checks) finds out-of-bounds write flaws before deployment.
Requiring documented secure-development standards and tools can mandate bounds-checked coding practices that avoid the weakness.
Input validation can structurally reject or sanitize data that would otherwise trigger an out-of-bounds write.
Memory-protection mechanisms limit the exploitability and blast radius of a successful out-of-bounds write.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure-development practices (static analysis, bounds checking, code review) are the primary means of preventing out-of-bounds writes.
Vulnerability scanning and recording can discover out-of-bounds write flaws so they can be remediated.
Patching or replacing vulnerable software directly eliminates known instances of this coding weakness.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect and prevent out-of-bounds write defects.
Secure development life cycle mandates practices that prevent out-of-bounds writes.
Application security requirements can specify bounds-checking and safe memory handling.
Secure architecture and engineering principles reduce the likelihood of buffer overflows.
Secure coding directly addresses out-of-bounds writes through language choice and coding standards.
Change management can enforce review gates that catch unsafe memory operations before deployment.