CVE-2026-87028: Concrete CMS 9 through 9.5.3 did not confirm that a board InstanceItem submitted to the custom-slot preview en

Routine

MEDIUM 6.5UPGRADE

CVE-2026-87028 is a medium-severity flaw (CVSS 6.5) affecting concrete cms. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Concrete CMS 9 through 9.5.3 did not confirm that a board InstanceItem submitted to the custom-slot preview endpoint belonged to the board instance the requesting user was authorized to edit, and did not enforce page-view permission before generating page-backed summary content. As a result, an authenticated user holding edit-board-contents permission on a single board instance could submit the identifier of an item belonging to a different board

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.4% (top 69%)
CISA exploited list	No
Weakness	CWE-862
Published	2026-09-16
Last modified	2026-09-21

Publisher (CNA): ConcreteCMS · Vendor: concretecms

Last updated 2026-09-21 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-16 17:18 UTCPublished CVE record published
2026-09-21 17:51 UTCUpdated Record last modified

concretecms concrete cms UPGRADE

Affected: >= 9.0.0 and < 9.5.3

Fixed in: 9.5.3

Safe to downgrade to: a release before 9.0.0

1. Check installed version

apt-cache policy concrete-cms || rpm -q concrete-cms || concrete-cms --version

2. UPGRADE to 9.5.3 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade concrete-cms

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade concrete-cms

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 9.0.0 (Debian / Ubuntu)

apt-cache madison concrete-cms sudo apt install concrete-cms=<VERSION_BEFORE_9.0.0> sudo apt-mark hold concrete-cms

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

dnf --showduplicates list concrete-cms sudo dnf downgrade concrete-cms-<VERSION_BEFORE_9.0.0> sudo dnf versionlock add concrete-cms

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-2026-87028?

concrete cms: upgrade to 9.5.3. Exact commands for each OS are on this page.

Is CVE-2026-87028 being exploited?

CVE-2026-87028 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-2026-87028 affect?

CVE-2026-87028 affects concrete cms. Severity is medium (CVSS 6.5). Concrete CMS 9 through 9.5.3 did not confirm that a board InstanceItem submitted to the custom-slot preview endpoint belonged to the board instance the requesting user was authorized to edit, and did not enforce page-view permission before

How urgent is CVE-2026-87028?

Priority 31/100. No elevated risk signals yet.

Related CVEs

CVE-2026-18111 MEDIUM 6.1 UPGRADE Concrete CMS 9 before 9.5.3 was vulnerable to stored cross-site scripting (XSS) in the Feature, Feature Link,
CVE-2026-18117 MEDIUM 5.4 UPGRADE Concrete CMS 9.0.0 through 9.5.3 is vulnerable to stored XSS via the custom page alias name (customAliasName)
CVE-2026-68526 MEDIUM 4.3 UPGRADE Concrete CMS before 9.5.3 did not validate an anti-CSRF token in the Calendar event duplicate dialog controlle
CVE-2026-81912 MEDIUM 5.7 UPGRADE Concrete CMS before 9.5.3 is vulnerable to Cross-Site Request Forgery in the Move Multiple Groups feature
CVE-2026-81913 MEDIUM 6.1 UPGRADE Concrete CMS versions 9.5.0 through 9.5.2 are vulnerable to Open Redirect via the rcURL parameter

References

← Back to latest CVEs