How severe is CVE-2026-45104?

CVE-2026-45104 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-45104 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (24th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-45104?

CVE-2026-45104 affects Osgeo Mapserver. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-45104?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-45104 have an EU (EUVD) identifier?

Yes. CVE-2026-45104 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-32631.

When was CVE-2026-45104 published?

CVE-2026-45104 was published on 2026-05-27 and last updated on 2026-06-17.

CVE-2026-45104

CVE-2026-45104 is a high-severity vulnerability in Osgeo Mapserver with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 0% (24th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-32631
Weakness: CWE-476
Affected product: Osgeo Mapserver
Published: 2026-05-27
Last modified: 2026-06-17

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.

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.
How severe is CVE-2026-45104?: CVE-2026-45104 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-45104 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (24th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-45104?: CVE-2026-45104 affects Osgeo Mapserver. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-45104?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-45104 have an EU (EUVD) identifier?: Yes. CVE-2026-45104 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-32631.
When was CVE-2026-45104 published?: CVE-2026-45104 was published on 2026-05-27 and last updated on 2026-06-17.

References

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

Affected products (1)

cpe:2.3:a:osgeo:mapserver:*:*:*:*:*:*:*:*

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