CVE-2026-45104: mapserver Null Dereference

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.

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CVSS v3.1 Score

7.5

HIGH

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

EPSS — Exploit Prediction

0.0028

Probability of exploitation

0.19%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-129 CWE-129

CWE-476 CWE-476

Affected Products

Vendor	Product	Versions
osgeo	mapserver	6.4.0 — 8.6.3

References

Advisories & Patches

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

Exploits

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

Frequently Asked Questions

What is 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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-45104? +

CVE-2026-45104 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0028, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-45104? +

CVE-2026-45104 affects products from osgeo, specifically: mapserver. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-45104? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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