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Concrete CmsApplication · Concretecms

CVE-2026-7890

MEDIUM · 6.4 CVSS v3.1 Published 2026-05-21
Fix available
A fix is available. Upgrade to 9.5.1 or later.
See remediation →
70/100
Remediation priority · Elevated
Remotely reachable Zero-click

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
In Concrete CMS 9.5.0 and below, the RSS Displayer block accepts a feed URL from any page editor and fetches it server-side without validation enabling redirect-to-internal bypasses.  The Concrete CMS security team gave this vulnerability a CVSS v.4.0 score of 2.1 with a vector CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:L/VA:N/SC:L/SI:N/SA:N.

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

This is a Server-Side Request Forgery (SSRF) vulnerability in Concrete CMS where the RSS Displayer block accepts a feed URL from page editors and fetches it server-side without validation. This enables attackers to make the server request internal resources by using redirect URLs, bypassing network isolation and potentially accessing internal services or sensitive data.

MitigationImplement strict URL validation with an allowlist of permitted domains before fetching feeds, and disable automatic follow redirects when making server-side HTTP requests.

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:< 9.5.1

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
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/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. Confirm Concrete CMS version
    Check the installed Concrete CMS version by examining the application/core/VERSION file or accessing the dashboard at /dashboard/system/information
    Affected if The installed version is below 9.5.1 (e.g., 9.5.0, 9.4.x, etc.)
  2. Identify if RSS Displayer block is in use
    Search for pages using the RSS Displayer block via the dashboard at /dashboard/pages/types or by searching the blocks table in the database for block_type_handle = 'rss_displayer'
    Affected if The RSS Displayer block is present and configured on any page in the site
  3. Locate RSS Displayer block code
    Examine the file system for packages/.../blocks/rss_displayer/ controller.php or similar path under the Concrete CMS installation directory
    Affected if The RSS Displayer block exists and the controller contains code that accepts a feed_url parameter without validation
  4. Check feed URL handling in block controller
    Inspect the controller file for fetch or HTTP request logic (e.g., file_get_contents, curl, GuzzleHttp) that processes the feed URL without validating it is an external HTTP(S) endpoint
    Affected if The code makes server-side requests using user-provided URLs without validating the URL scheme, hostname, or IP address
  5. Verify URL validation is absent
    Search the block controller and related PHP files for URL validation functions such as filter_var, parse_url checks, or whitelist patterns for http/https only
    Affected if No validation exists to restrict feed URLs to external HTTP/HTTPS endpoints or reject internal IP ranges, localhost, or non-HTTP schemes like file://

A user is affected if they run Concrete CMS version below 9.5.1 AND have the RSS Displayer block enabled, as the block accepts arbitrary URLs without server-side validation.

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 9.5.1 or later
Fixed in 9.5.1
Interim mitigation

Implement strict URL validation with an allowlist of permitted domains before fetching feeds, and disable automatic follow redirects when making server-side HTTP requests.

Recommended fix High confidence

9.5.1

  1. Back up your Concrete CMS database and files.
  2. Download Concrete CMS version 9.5.1 from the official Concrete CMS release channels.
  3. Replace the existing files with the new version files.
  4. Run the upgrade process (e.g., via the dashboard or command line).
  5. Clear the application cache.
  6. Verify that the RSS Displayer block works correctly and the vulnerability is remediated.

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

Fix this in Concrete Cms Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.

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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-2026-7890 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