Is CVE-2026-45104 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-45104 being exploited in the wild.

How severe is CVE-2026-45104?

High severity, with a CVSS score of 7.5, published 27 May 2026.

Is there a fix for CVE-2026-45104?

A patch was published on 2026-05-27: Fixed in version 8.6.3 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-45104 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-45104?

Check whether you run MapServer at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-45104: MapServer NULL pointer dereference in SLD ElseFilter parsing

CVE-2026-45104 · Severity: high · CVSS 7.5 · Published 2026-05-27

MapServer, a popular open-source platform for publishing spatial data and interactive mapping applications, is vulnerable to a remote denial-of-service attack. An unauthenticated attacker can send a specially crafted, small mapping style request (SLD) to a MapServer web service, causing the application to crash. This can lead to service outages, particularly in environments where MapServer handles multiple requests simultaneously.

Technologies: MapServer. Vendors: MapServer.

Quick answers

Is CVE-2026-45104 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-45104 being exploited in the wild.
How severe is CVE-2026-45104?: High severity, with a CVSS score of 7.5, published 27 May 2026.
Which products and versions are affected?: MapServer 6.4.0 to 8.6.2.
Is there a fix for CVE-2026-45104?: A patch was published on 2026-05-27: Fixed in version 8.6.3 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-45104 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-45104?: Check whether you run MapServer at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A NULL pointer dereference exists in MapServer's SLD parsing logic within `src/mapogcsld.cpp`. The function `msSLDParseUserStyle` incorrectly assumes that any `<Rule>` containing an `<ElseFilter/>` will result in the creation of exactly one new class via `msSLDParseRule`. However, if the rule contains no symbolizers (which is structurally valid SLD), `msSLDParseRule` adds zero classes. Subsequent logic in `_SLDApplyRuleValues` then attempts to index `psLayer->_class` with a value of -1, causing a crash. This is reachable unauthenticated via the WMS `SLD_BODY` or `SLD` parameters, which are enabled by default. The vulnerability is fixed in version 8.6.3 by calculating the actual number of classes added rather than assuming a constant value.

Affected products

MapServer MapServer 6.4.0 to 8.6.2

Timeline

2026-05-07: advisory: GitHub Security Advisory published
2026-05-27: disclosed: CVE published to NVD
2026-05-27: patched: Fixed in version 8.6.3

References

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

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