CVE-2026-45104: MapServer is a system for developing web-based GIS applications

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HIGH 7.5REMOTEUPGRADE

CVE-2026-45104 is a high-severity flaw (CVSS 7.5) affecting mapserver. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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-form

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 75%)
CISA exploited list	No
Weakness	CWE-129, CWE-476
Published	2026-05-27
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: osgeo

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-27 20:16 UTCPublished CVE record published
2026-06-17 10:51 UTCUpdated Record last modified

osgeo mapserver UPGRADE

Affected: >= 6.4.0 and < 8.6.3

Fixed in: 8.6.3

Safe to downgrade to: a release before 6.4.0

1. Check installed version

apt-cache policy mapserver || rpm -q mapserver || mapserver --version

2. UPGRADE to 8.6.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mapserver

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mapserver

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 6.4.0 (Debian / Ubuntu)

apt-cache madison mapserver sudo apt install mapserver=<VERSION_BEFORE_6.4.0> sudo apt-mark hold mapserver

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list mapserver sudo dnf downgrade mapserver-<VERSION_BEFORE_6.4.0> sudo dnf versionlock add mapserver

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-45104?

mapserver: upgrade to 8.6.3. Exact commands for each OS are on this page.

Is CVE-2026-45104 being exploited?

CVE-2026-45104 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-45104 affect?

CVE-2026-45104 affects mapserver. Severity is high (CVSS 7.5). 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 o

How urgent is CVE-2026-45104?

Priority 42/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-42030 MEDIUM 6.1 UPGRADE MapServer is a system for developing web-based GIS applications

References

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