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Concrete CmsApplication · Concretecms

CVE-2023-28820

MEDIUM · 5.4 CVSS v3.1 Published 2023-04-28
Fix available
A fix is available. Upgrade to 9.1.0 or later.
See remediation →
58/100
Remediation priority · Elevated
Remotely reachable

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Concrete CMS (previously concrete5) before 9.1 is vulnerable to stored XSS in RSS Displayer via the href attribute because the link element input was not sanitized.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Concrete CMS versions before 9.1 contain a stored XSS vulnerability in the RSS Displayer component. The vulnerability stems from insufficient sanitization of the href attribute in link elements, allowing authenticated attackers to inject malicious JavaScript that persists and executes when other users view the affected RSS feed display.

MitigationUpgrade Concrete CMS to version 9.1 or later which includes proper input sanitization for link elements in the RSS Displayer. If immediate upgrading is not feasible, restrict administrative access to the RSS Displayer component until the patch can be applied.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Concrete CmsApplication
Affected:< 9.1.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Concrete CMS installation
    Locate the Concrete CMS installation directory and check for the cms/CHANGELOG.md or composer.json file to find the installed version number
    Affected if The installed version is below 9.1.0
  2. Verify RSS Displayer is in use
    Access the Concrete CMS dashboard and navigate to the Blocks or Pages sections to determine if any pages contain the RSS Displayer block component
    Affected if RSS Displayer blocks are present on any published pages
  3. Check for authenticated access
    Review user accounts and permissions within Concrete CMS admin panel to identify which user roles have access to edit pages containing RSS Displayer blocks
    Affected if Multiple users or roles have edit permissions on pages with RSS Displayer blocks
  4. Inspect RSS feed source configuration
    If RSS Displayer blocks exist, examine the configured RSS feed URLs and verify whether they accept user-supplied input or come from untrusted external sources
    Affected if The RSS feed URLs are sourced from untrusted or user-controllable locations

You are affected if running Concrete CMS version below 9.1.0 AND the RSS Displayer block is in use on accessible pages, allowing authenticated users to inject malicious href attributes that execute when others view the feed.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 9.1.0 or later
Fixed in 9.1.0
Interim mitigation

Upgrade Concrete CMS to version 9.1 or later which includes proper input sanitization for link elements in the RSS Displayer. If immediate upgrading is not feasible, restrict administrative access to the RSS Displayer component until the patch can be applied.

Recommended fix High confidence

Concrete CMS 9.1.0 or later

  1. 1. Backup your current Concrete CMS installation and database before proceeding with any upgrade.
  2. 2. Download Concrete CMS version 9.1.0 or later from the official source at www.concretecms.org.
  3. 3. Replace the existing Concrete CMS files with the new version 9.1.0 files, preserving your configuration and application files.
  4. 4. Run the database upgrade script if prompted during the upgrade process.
  5. 5. Clear all caches after the upgrade to ensure the new code is loaded.
  6. 6. Verify the RSS Displayer functionality is working correctly after the upgrade.
  7. 7. Test that the stored XSS vulnerability in the RSS Displayer link element has been remediated by attempting to inject malicious script in the href attribute.
Caveat Review the Concrete CMS 9.1.0 release notes for any breaking changes or configuration updates that may affect your site

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Concrete Cms Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,080
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-28820 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data