CVE-2026-45104

MapServer: NULL pointer dereference in SLD `<ElseFilter>` rule parsing reachable via WMS `SLD_BODY`

State: Published
Severity: 7.5 High
Published: May 27, 2026
Updated: Jun 1, 2026
Reserved: May 8, 2026

Description

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.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	GitHub_M

Weaknesses

CWE-129 Improper Validation of Array Index
CWE-476 NULL Pointer Dereference

Affected Products

Product	Versions
MapServerMapServer	>= 6.4.0, < 8.6.3Affected

References

https://github.com/MapServer/MapServer/security/advisories/GHSA-4h8g-378q-r75m

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