What is CVE-2026-45104?

CVE-2026-45104 is a high-severity vulnerability in Mapserver, classified under Improper Validation of Array Index. CVSS score: 7.5/10. Published 2026-05-27.

How severe is CVE-2026-45104?

High severity. CVSS v3 base score is 7.5 out of 10.

NULL pointer dereference in Mapserver

CVE-2026-45104

MapServer is a system for developing web-based GIS applications. From 6.4.0 to before 8.6.3, msSLDParseUserStyle always calls _SLDApplyRuleValues(psRule, psLayer, 1); for any <Rule> carrying <ElseFilter/> — it assumes msSLDParseRule added one class. When the rule has no symbolizer (a structurally valid SLD), msSLDParseRule adds zero, and _SLDApplyRuleValues ends up indexing _class[-1], resulting in a NULL pointer dereference. A 200-byte well-formed SLD via the WMS SLD_BODY= parameter is enough to trigger this, no auth required. This vulnerability is fixed in 8.6.3.

Published 2026-05-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.005 (39.4th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 39th percentile — 39.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.005 · change: +0.002

Affected products

Mapserver — versions >= 6.4.0, < 8.6.3
Osgeo Mapserver

Weakness classification (CWE)

References

github.com/MapServer/MapServer/security/advisories/GHSA-4h8g-378q-r75m (Exploit, Mitigation, Vendor Advisory)

Frequently asked questions

What is CVE-2026-45104?: CVE-2026-45104 is a high-severity vulnerability in Mapserver, classified under Improper Validation of Array Index. CVSS score: 7.5/10. Published 2026-05-27.
How severe is CVE-2026-45104?: High severity. CVSS v3 base score is 7.5 out of 10.