Security readout for executives and security teams
Plain-English summary
Concrete CMS through 8.5.5 allowed certain users to make the server fetch content from redirected URLs. That could expose internal network files or services to someone with remote-upload permissions, and could also bypass file type restrictions.
Executive priority
Prioritize remediation for internet-facing Concrete CMS sites or sites with many content users. Business risk is internal data exposure through the CMS server, not just malicious file upload.
Technical view
The issue is server-side request forgery in Concrete CMS external-site upload handling. A permitted user can submit a URL that redirects to an internal resource; the server follows the redirect and loads that content, including disallowed file types.
Likely exposure
Exposure is most likely on Concrete CMS sites through 8.5.5 where users can upload files from external sites. The source does not show unauthenticated exposure.
Exploitation context
The bundle cites a HackerOne report and marks CISA KEV as false. No provided source states active exploitation in the wild.
Researcher notes
Key constraints are permission-dependent access and redirect-following behavior. The source bundle lacks CVSS, CWE mapping, detailed patch text, and proof of active exploitation, so validation should stay focused on version, permission scope, and upload behavior.
Mitigation direction
- Inventory Concrete CMS instances and confirm whether any run 8.5.5 or earlier.
- Review Concrete CMS 8.5.6 release notes and apply vendor upgrade guidance.
- Restrict external-site upload permission to trusted administrators until remediation is complete.
- Limit CMS server outbound access to internal networks where operationally possible.
- Review uploaded files and logs for unusual redirected external-upload activity.
Validation and detection
- Confirm the running Concrete CMS version on all public and internal sites.
- Audit roles with permission to upload files from external sites.
- Review web and application logs for remote upload attempts involving redirects.
- Verify file upload controls reject disallowed file types after remediation.
- Check server egress rules for access to internal-only resources.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
Cloud metadata behavior lookup
The CVE wording references SSRF or metadata access, so cloud discovery and credential material review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-40109 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://hackerone.com/reports/1102105CVE reference · x_refsource_MISC
- https://documentation.concretecms.org/developers/introduction/version-history/856-release-notesCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.