# CVE-2026-33721: MapServer has heap buffer overflow in SLD `Categorize` Threshold parsing

- Exploited (CISA KEV): no
- Published: 2026-03-27
- CVSS: 5.3 MEDIUM (v3.1)
- EPSS: 1.2% (69th percentile)
- CWE: CWE-787

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.

## Edge WAF coverage (claimed by vendors, not measured)

| Vendor | Status | First rule | Days after publication |
|---|---|---|---|
| Cloudflare | No public claim | — | — |
| AWS | No public claim | — | — |
| Microsoft Azure | No public claim | — | — |
| Google Cloud | No public claim | — | — |
| Fastly | Before feed history | — | — |
| F5 | Rule published | 2026-09-16 | 173 |
| Akamai | No public source | — | — |
| OWASP CRS | No public claim | — | — |

### F5

- 2026-09-16 · new · rule 200011111
  > Added: signature 200011111 "MapServer Denial Of Service" (Buffer Overflow, risk Medium), systems: Other Web Server. References: CVE-2026-33721.
  Source: https://docs.cloud.f5.com/docs-v2/platform/changelogs/security-details-changelog

"No public claim" means no vendor statement names this CVE; "Before feed history" means the CVE is older than the vendor feed. In both cases generic rules may still block it.

HTML: https://cve.vigilbase.com/cve/CVE-2026-33721 · JSON: https://cve.vigilbase.com/api/v1/cves/CVE-2026-33721