# CVE-2026-45104: MapServer: NULL pointer dereference in SLD `<ElseFilter>` rule parsing reachable via WMS `SLD_BODY`

> Unauthenticated attackers can cause a denial of service in MapServer by sending a malformed SLD_BODY parameter to the WMS interface.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 May 2026
- **Updated:** 1 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-45104, GHSA-4h8g-378q-r75m, UBUNTU-CVE-2026-45104

## What is CVE-2026-45104?

CVE-2026-45104 is a high-severity vulnerability in MapServer, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-476 (NULL Pointer Dereference), CWE-129 (Improper Validation of Array Index)

## Which versions are affected by CVE-2026-45104?

It affects 1 product.


Products: Osgeo Mapserver.

## How do I fix CVE-2026-45104?

Upgrade to a fixed version.

## Is CVE-2026-45104 being exploited?

There is no known exploitation of CVE-2026-45104 in the wild and no public exploit code.

## Other vulnerabilities in MapServer

- [CVE-2010-2540](https://insights.sbomify.com/CVE-2010-2540/): Security feature bypass in n/a (critical 10.0)
- [CVE-2009-2281](https://insights.sbomify.com/CVE-2009-2281/): Memory corruption in n/a (critical 10.0)
- [CVE-2009-0839](https://insights.sbomify.com/CVE-2009-0839/): Memory corruption in n/a (critical 10.0)
- [CVE-2009-0840](https://insights.sbomify.com/CVE-2009-0840/): Memory corruption in n/a (critical 10.0)
- [CVE-2009-0841](https://insights.sbomify.com/CVE-2009-0841/): Path traversal in n/a (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45104 and fix it if it is affected.

What it is: CVE-2026-45104 is a high-severity vulnerability in MapServer, published on 27 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-45104 in the wild and no public exploit code.

Affected product: MapServer. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45104/ (Markdown: https://insights.sbomify.com/CVE-2026-45104/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45104
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45104
- OSV: https://osv.dev/vulnerability/CVE-2026-45104

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45104/
Summaries are generated and may contain mistakes; the official description above is the record.